06 piston eng ignition

RECIPROCATINGRECIPROCATING
ENGINE IGNITIONENGINE IGNITION
AND STARTINGAND STARTING
SYSTEMSYSTEM

RECIPROCATING ENGINE IGNITION SYSTEMSRECIPROCATING ENGINE IGNITION SYSTEMS
• Ignition event in four stroke cycle engine.Ignition event in four stroke cycle engine.
• Four stroke cycle engine consists of five events;Four stroke cycle engine consists of five events;
i) Intakei) Intake
ii) Compression.ii) Compression.
iii) Ignition.iii) Ignition.
iv) Power.iv) Power.
v) Exhaust.v) Exhaust.
• Ignition takes place during compression stroke in third event.Ignition takes place during compression stroke in third event.
• Fuel/air mixture burnt in the cylinder produce heat energy thanFuel/air mixture burnt in the cylinder produce heat energy than
converted to mechanical energy.converted to mechanical energy.

Engine Ignition systemEngine Ignition system
• To produce/delivering high voltage spark to each cylinderTo produce/delivering high voltage spark to each cylinder
under all operating condition.under all operating condition.
• Must be able to deliver spark at specific time. (i.e. 24Must be able to deliver spark at specific time. (i.e. 24°° BTDC)BTDC)
• Must be high degree of reliability.Must be high degree of reliability.
• Must have dual systems (as stated in FAR Part 33).Must have dual systems (as stated in FAR Part 33).
i) Dual ignition system.i) Dual ignition system.
ii) Two spark plugs for each cylinder.ii) Two spark plugs for each cylinder.
iii) Two separate electrical system.iii) Two separate electrical system.
• Advantages using two magneto systems;Advantages using two magneto systems;
a) One system serve as back up if other system fail.a) One system serve as back up if other system fail.
b) Two spark plugs in one cylinder, increases combustionb) Two spark plugs in one cylinder, increases combustion
efficiency engine power output.efficiency engine power output.

Engine Ignition SystemsEngine Ignition Systems
• System used either;System used either;
a) Battery ignition system.a) Battery ignition system.
b) Magneto ignition system.b) Magneto ignition system.
c) Combination of the two.c) Combination of the two.
BATTERY IGNITION SYSTEMBATTERY IGNITION SYSTEM
• Utilized a battery as source of electrical energy.Utilized a battery as source of electrical energy.
• This system consists of:-This system consists of:-
i) Battery. ii) Ignition switch.i) Battery. ii) Ignition switch.
iii) Ignition coil. iv) Breaker point.iii) Ignition coil. iv) Breaker point.
v) Capacitor. vi) Cam.v) Capacitor. vi) Cam.
vii) Distributor. viii) H.T. leadvii) Distributor. viii) H.T. lead
ix) Spark plugs.ix) Spark plugs.

Battery Ignition SystemBattery Ignition System

IGNITION SYSTEMSIGNITION SYSTEMS

 Battery.Battery.
- The source of electrical power.- The source of electrical power.
 Ignition switch.Ignition switch.
- In the cockpit, “ON” circuit closed and “OFF” circuit open.- In the cockpit, “ON” circuit closed and “OFF” circuit open.
 Ignition coil.Ignition coil.
- Consists of:- Primary winding - received current from battery.- Consists of:- Primary winding - received current from battery.
Secondary winding – step up voltage.Secondary winding – step up voltage.
 Breaker point/contact point.Breaker point/contact point.
- Convert the pure DC to pulsating DC.- Convert the pure DC to pulsating DC.
- Mechanical device with two electrical contact (close & open) at regular- Mechanical device with two electrical contact (close & open) at regular
interval.interval.
- Connected in series with coil and parallel with capacitor.- Connected in series with coil and parallel with capacitor.
 Capacitor / Condenser.Capacitor / Condenser.
- To prevent arcing across the contact points.- To prevent arcing across the contact points.
- Speed up the collapsing of magnetic field.- Speed up the collapsing of magnetic field.

 Cam.Cam.
- Consist of metallic disc with two or more raised lobes.- Consist of metallic disc with two or more raised lobes.
- Opens and closes the breaker point.- Opens and closes the breaker point.
 Distributor.Distributor.
- Distributes high voltage from the coil to spark plug.- Distributes high voltage from the coil to spark plug.
- Consist of rotating finger and distribution block.- Consist of rotating finger and distribution block.
 High tension lead.High tension lead.
- Conductors that convey high voltage from distributor to- Conductors that convey high voltage from distributor to
individual spark plugs.individual spark plugs.
 Spark plug.Spark plug.
- Produce high energy of spark to ignite fuel/air mixture in- Produce high energy of spark to ignite fuel/air mixture in
cylinder at specific time.cylinder at specific time.

MAGNETO IGNITION SYSTEMSMAGNETO IGNITION SYSTEMS
♣ Magneto is a permanent magnet ACMagneto is a permanent magnet AC
generator.generator.
♣ It uses electromagnetic and induced currentIt uses electromagnetic and induced current
principles to develop high voltage to createprinciples to develop high voltage to create
spark.spark.
♣ Designated as either;Designated as either;
a) High tension systems.a) High tension systems.
b) Low tension systems.b) Low tension systems.

Magneto Ignition systemsMagneto Ignition systems
a)a) High-Tension Systems.High-Tension Systems.
>> System include a single high-tension magneto.System include a single high-tension magneto.
>> A wiring harness and a set of spark plug.A wiring harness and a set of spark plug.
>> Utilizes a rotating magnet instead of battery.Utilizes a rotating magnet instead of battery.
>> Consist of primary and secondary winding.Consist of primary and secondary winding.
>> The coil steps up the voltage before it goes toThe coil steps up the voltage before it goes to
distributor and to spark plugs.distributor and to spark plugs.

Magneto Ignition SystemsMagneto Ignition Systems
High Tension Magneto System.High Tension Magneto System.

High Tension SystemHigh Tension System
●● High tension magnetosHigh tension magnetos
are available either;are available either;
a) Single magneto ora) Single magneto or
b) Dual magneto.b) Dual magneto.
Single magnetoSingle magneto..
●● Consists of a permanentConsists of a permanent
magnet having two, fourmagnet having two, four
or eight poles.or eight poles.
●● Fixed to a single rotatingFixed to a single rotating
shaft.shaft.
●● Two single magnetosTwo single magnetos
must be installed on amust be installed on a
single engine.single engine.

High Tension SystemsHigh Tension Systems
Dual magnetoDual magneto..
• Contain two independentContain two independent
ignition system that shareignition system that share
a common rotatinga common rotating
magnet.magnet.
• Dual magneto containsDual magneto contains
two of everything excepttwo of everything except
the rotating magnet andthe rotating magnet and
cam.cam.

• Problem on early high tension magneto.Problem on early high tension magneto.
• FlashoverFlashover is a term used to describe an occurrence inside the high-tensionis a term used to describe an occurrence inside the high-tension
magneto where a spark jumps to the wrong electrode.magneto where a spark jumps to the wrong electrode.
• High altitude operation increase the possibility of flashover due to lower airHigh altitude operation increase the possibility of flashover due to lower air
density.density.
• Flashover can lead to carbon tracking, which appears as a fine-like carbonFlashover can lead to carbon tracking, which appears as a fine-like carbon
trail inside the distributor.trail inside the distributor.
• To prevent it;To prevent it;
> Made distributor larger to increase the distance.> Made distributor larger to increase the distance.
> Use low-tension magnetos – supplies low voltage to a high> Use low-tension magnetos – supplies low voltage to a high
tension transformer at the spark plug.tension transformer at the spark plug.
> Pressurized the magnetos with air above ambient to make spark difficult to> Pressurized the magnetos with air above ambient to make spark difficult to
jump at high altitudes.jump at high altitudes.
> Insulation on the ignition components.> Insulation on the ignition components.

• To prevent it;To prevent it;
> Made distributor larger to increase the distance.> Made distributor larger to increase the distance.
> Use low-tension magnetos – supplies low voltage to> Use low-tension magnetos – supplies low voltage to
a high tension transformer at the spark plug.a high tension transformer at the spark plug.
> Pressurized the magnetos with air above ambient to> Pressurized the magnetos with air above ambient to
make spark difficult to jump at high altitudes.make spark difficult to jump at high altitudes.
> Insulation on the ignition components.> Insulation on the ignition components.

Low Tension SystemsLow Tension Systems
• Designed to overcome the flashover.Designed to overcome the flashover.
• Magneto coil has only one winding.Magneto coil has only one winding.
• Delivered low voltage to kept flashover at its minimum.Delivered low voltage to kept flashover at its minimum.
• Utilize high-tension transformers (low ►high voltage).Utilize high-tension transformers (low ►high voltage).
• Consist of primary and secondary coil.Consist of primary and secondary coil.
• Add more components.Add more components.

Low Tension SystemLow Tension System

Magneto Operating PrinciplesMagneto Operating Principles
 High and low-tension magneto systems operates on theHigh and low-tension magneto systems operates on the
same principle for generating electrical power.same principle for generating electrical power.
 Low-tension not use in modern a/c.Low-tension not use in modern a/c.
 High-tension magneto consists of;High-tension magneto consists of;
a) Mechanical system.a) Mechanical system.
b) Magnetic circuit.b) Magnetic circuit.
c) Primary electrical circuit.c) Primary electrical circuit.
d) Secondary electrical circuit.d) Secondary electrical circuit.
 Ignition switch in the cockpit control the operation ofIgnition switch in the cockpit control the operation of
this circuit.this circuit.

a) Mechanical Systema) Mechanical System
 Includes of;Includes of;
- Housing.- Housing.
- Magneto drive shaft.- Magneto drive shaft.
- All non-electrical portion of- All non-electrical portion of
magneto.magneto.
 Housing.Housing.
- Made of aluminum – not interfere with magnetic- Made of aluminum – not interfere with magnetic
circuit.circuit.
- Light in weight.- Light in weight.
- Mechanical strength and rigidity.- Mechanical strength and rigidity.
 Drive shaft.Drive shaft.
- Single hardened steel.- Single hardened steel.
- Mounted onto this drive shaft;- Mounted onto this drive shaft;
- Rotating magnet.- Rotating magnet.
- Cam.- Cam.
- Gear to drive a distributor finger.- Gear to drive a distributor finger.
- Supported by either ball or needle bearing.- Supported by either ball or needle bearing.

Mechanical system conts.Mechanical system conts.
 Magneto housing design with two types of mounting;Magneto housing design with two types of mounting;
a)a) Base-mounted magnetoBase-mounted magneto..
- Bolted rigidly to a bracket on the engine- Bolted rigidly to a bracket on the engine
accessory case.accessory case.
b)b) Flange-mounted magnetoFlange-mounted magneto..
- Used on opposed engine.- Used on opposed engine.
- Mounting flange cast as an integral part of the housing.- Mounting flange cast as an integral part of the housing.
- Mounting holes in the flange are not circular.- Mounting holes in the flange are not circular.
- L-shape lockdown tabs to clamp the flange to the engine.- L-shape lockdown tabs to clamp the flange to the engine.
- Facilitates for slight magneto adjustment to the engine- Facilitates for slight magneto adjustment to the engine
timing.timing.

Mechanical system conts.Mechanical system conts.
• Two types of cams used in high-tension magnetos:-Two types of cams used in high-tension magnetos:-
Uncompensated and compensated cam.Uncompensated and compensated cam.
 Uncompensated camUncompensated cam..
- Has uniform distant between the lopes.- Has uniform distant between the lopes.
- Equal degree of crankshaft rotation.- Equal degree of crankshaft rotation.
- Number of lubes is equal to the number of poles- Number of lubes is equal to the number of poles
on the rotating cam.on the rotating cam.

Mechanical System conts.Mechanical System conts.
 Compensated camCompensated cam..
- Fitted to radial engine.- Fitted to radial engine.
- Separate cam lobe for each engine.- Separate cam lobe for each engine.
- Firing event not uniform.- Firing event not uniform.
- Spacing between each lobe is tailored to a particular- Spacing between each lobe is tailored to a particular
cylinder.cylinder.
- Cam complete one revolution at every two- Cam complete one revolution at every two
revolution of crankshaft.revolution of crankshaft.
- Driven by gear train.- Driven by gear train.

Magnetic circuitMagnetic circuit
• Consist of:-Consist of:-
- Rotating permanent magnet.- Rotating permanent magnet.
- Poles shoes.- Poles shoes.
- Poles shoes extension.- Poles shoes extension.
- Coil core.- Coil core.
• Rotating magnet may be have two, four or eight magnetic poles.Rotating magnet may be have two, four or eight magnetic poles.
• Arranged with alternating north and south poles that spacedArranged with alternating north and south poles that spaced
evenly around the magneto drive shaft.evenly around the magneto drive shaft.
• Made of Alnico (an alloy of aluminum, iron, nickel and cobalt)Made of Alnico (an alloy of aluminum, iron, nickel and cobalt)
and retains magnetism for an indefinite length of time.and retains magnetism for an indefinite length of time.
• Also made of Permalloy with similar qualities.Also made of Permalloy with similar qualities.

 The rotating magnet, rotated by the engine through the gearing and rotateThe rotating magnet, rotated by the engine through the gearing and rotate
between the two poles.between the two poles.
 Pole shoes are joined up by coil core in order to complete the circuit.Pole shoes are joined up by coil core in order to complete the circuit.
 Coil core and pole shoes are laminated by the layers of high grade soft iron.Coil core and pole shoes are laminated by the layers of high grade soft iron.
 The laminated layers reduces eddy current, keep magneto cooler and boostingThe laminated layers reduces eddy current, keep magneto cooler and boosting
efficiency.efficiency.
 Allows flux lines to pass through it easily.Allows flux lines to pass through it easily.

(A)(A) When the magnetic poles are aligned with theWhen the magnetic poles are aligned with the
pole shoes, maximum number of flux linespole shoes, maximum number of flux lines
flow through the core. ( flux flow from north to south )flow through the core. ( flux flow from north to south )
- Create the strongest magnetic field.- Create the strongest magnetic field.
- This known as full register position.- This known as full register position.

Neutral positionNeutral position
• When the magnet poles are in the neutral positionWhen the magnet poles are in the neutral position
(beyond full registered).(beyond full registered).
• The magnetic field collapsed.The magnetic field collapsed.
• No lines of flux pass through the coil core.No lines of flux pass through the coil core.

Full register positionFull register position
• Once past the neutral position, flux lines passingOnce past the neutral position, flux lines passing
through the coil’s core increases until magnet reachesthrough the coil’s core increases until magnet reaches
full register position again.full register position again.
• This time the flux lines flow in the opposite direction.This time the flux lines flow in the opposite direction.

Efficiency gap/E-gap angleEfficiency gap/E-gap angle
• Once the magnet rotates beyond magnetic neutral andOnce the magnet rotates beyond magnetic neutral and
magnetic field of opposite polarity starts to build, at thismagnetic field of opposite polarity starts to build, at this
point the greatest magnetic field exists.point the greatest magnetic field exists.
• E-gapE-gap – rotating magnet at the specific number of– rotating magnet at the specific number of
degrees passed/beyond the neutral position.degrees passed/beyond the neutral position.

Primary CircuitPrimary Circuit
 Consist of:Consist of:
a) Primary Winding.a) Primary Winding.
b) Set of breaker point.b) Set of breaker point.
c) Capacitor.c) Capacitor.

Primary CircuitPrimary Circuit
a) Primary Winding.a) Primary Winding.
 Magneto consists of 180 to 200 turn of 18 gaugeMagneto consists of 180 to 200 turn of 18 gauge
copper wire.copper wire.
 Wire coated with an enamel insulator.Wire coated with an enamel insulator.
 One end attach to ground lead and another end connect to theOne end attach to ground lead and another end connect to the
secondary winding.secondary winding.
b) Breaker point.b) Breaker point.
 Mounted to the magneto housing.Mounted to the magneto housing.
 Held closed by leaf-type spring and open by cam.Held closed by leaf-type spring and open by cam.
 Point open at the greatest magnet stress (E-gap).Point open at the greatest magnet stress (E-gap).
 Breaker point open interrupted the current flow and allowBreaker point open interrupted the current flow and allow
current to be induced into the secondary coil.current to be induced into the secondary coil.

Primary circuitPrimary circuit
c) Capacitorc) Capacitor
 Installed parallel with the breaker point and in series with ignition switch.Installed parallel with the breaker point and in series with ignition switch.
 Reduce acing when breaker point open.Reduce acing when breaker point open.
- Cause delay collapse of magnetic field in the primary lead.- Cause delay collapse of magnetic field in the primary lead.
- severe arcing could weld the point together.- severe arcing could weld the point together.
 Also reduce electromagnetic radiation from primary lead.Also reduce electromagnetic radiation from primary lead.
 Feed through/filter capacitor.Feed through/filter capacitor.
- Ground the radio frequency before its leave the magneto.- Ground the radio frequency before its leave the magneto.

Secondary CircuitSecondary Circuit
• Produces the high voltage energy requiredProduces the high voltage energy required
to cause spark.to cause spark.
• Make up of:Make up of:
- Secondary winding.- Secondary winding.
- Magneto coil.- Magneto coil.
- Distributor.- Distributor.
• Amount of current induced into theAmount of current induced into the
secondary winding depend on:secondary winding depend on:
- Rate of magnetic field around the- Rate of magnetic field around the
primary winding collapse.primary winding collapse.
- The ratio of winding between primary- The ratio of winding between primary
and secondary.and secondary.
- Coil made from approximately 13,000- Coil made from approximately 13,000
turns ofturns of fine wirefine wire..
- Capable of producing 20,000 volts pulse.- Capable of producing 20,000 volts pulse.
- One end attached to primary winding,- One end attached to primary winding,
path to ground and opposite end ispath to ground and opposite end is
attached to a high voltage contact atattached to a high voltage contact at
magneto body.magneto body.

Secondary circuitSecondary circuit
Distributor rotor.Distributor rotor.
• Allow current flow from secondaryAllow current flow from secondary
winding to the distributor.winding to the distributor.
• A spring loaded carbon brush mounted inA spring loaded carbon brush mounted in
the centre of the distributor rotor pressesthe centre of the distributor rotor presses
against the magneto contact.against the magneto contact.
• Distributor consist of a conductive arm orDistributor consist of a conductive arm or
finger that carries high voltage to thefinger that carries high voltage to the
electrode for each spark plug.electrode for each spark plug.
• Driven by a gear that is mounted to theDriven by a gear that is mounted to the
magneto drive shaft.magneto drive shaft.
• Distributor rotor is geared to provide aDistributor rotor is geared to provide a
high voltage path to distributor block athigh voltage path to distributor block at
definite points in its rotation.definite points in its rotation.
• Must complete one rev. for every two rev.Must complete one rev. for every two rev.
of crankshaft.of crankshaft.
• With 2:1 ratio, a magneto can fire all theWith 2:1 ratio, a magneto can fire all the
spark plugs.spark plugs.

Distributor blockDistributor block
• Constructed of a light-weightConstructed of a light-weight
insulating material.insulating material.
• Mounted in one half of the magnetoMounted in one half of the magneto
housing.housing.
• One side with electrodes and the otherOne side with electrodes and the other
side for receptacles for spark plugside for receptacles for spark plug
lead.lead.
• Electrodes and receptacles areElectrodes and receptacles are
arranged circumferentially around thearranged circumferentially around the
distributor block.distributor block.
• Each time the rotating magnet is inEach time the rotating magnet is in
the E-gap position the distributorthe E-gap position the distributor
finger lines up with an electrode andfinger lines up with an electrode and
deliver a high voltage pulse .deliver a high voltage pulse .
• Then routed through leads to sparkThen routed through leads to spark
plug.plug.

Safety GapSafety Gap
 Protect the secondary winding in a magneto coil.Protect the secondary winding in a magneto coil.
 Provide alternate path for current if there is an open inProvide alternate path for current if there is an open in
secondary circuit.secondary circuit.
 This backup ground path called safety gap.This backup ground path called safety gap.
 Connected in series with the secondary winding by twoConnected in series with the secondary winding by two
electrode.electrode.
 Any excessive voltage induce into the secondaryAny excessive voltage induce into the secondary
winding jumps to safety gap to ground.winding jumps to safety gap to ground.
 This to ensure voltage in the secondary winding doesThis to ensure voltage in the secondary winding does
not rise high enough to damage the magneto coil.not rise high enough to damage the magneto coil.

Magneto speedMagneto speed
 Distributor rotor in a magneto always rotate one-half the engineDistributor rotor in a magneto always rotate one-half the engine
crankshaft speed.crankshaft speed.
 Engine crankshaft must complete two rev. in order to fire eachEngine crankshaft must complete two rev. in order to fire each
spark plug once.spark plug once.
 Speed of the distributor is set, rotating magnet shaft varies withSpeed of the distributor is set, rotating magnet shaft varies with
the number of cylinders and number of poles.the number of cylinders and number of poles.
 Eg.Eg. Number of cylindersNumber of cylinders == 66 == 33 == 1½1½
2 x number of poles 2x2 42 x number of poles 2x2 4
- If engine turning at 2,000 rpm the magneto rotate at- If engine turning at 2,000 rpm the magneto rotate at
3,000 rpm.3,000 rpm.

Auxiliary Ignition SystemsAuxiliary Ignition Systems
• When magneto turns at slow speed, its produces relatively little voltage.When magneto turns at slow speed, its produces relatively little voltage.
• As magneto speed increases the amount of current induced into primaryAs magneto speed increases the amount of current induced into primary
circuit increases and produced higher voltage spark.circuit increases and produced higher voltage spark.
• At low magneto speed, voltage generated is insufficient to fire a spark plug.At low magneto speed, voltage generated is insufficient to fire a spark plug.
• To produce enough voltage to fire the spark plug is known asTo produce enough voltage to fire the spark plug is known as coming –oncoming –on
speedspeed..
• Speed is between 100 – 200 rpm.Speed is between 100 – 200 rpm.
• To start an eng. starter cannot crank eng. fast enough for magneto to reach itsTo start an eng. starter cannot crank eng. fast enough for magneto to reach its
coming – on speed.coming – on speed.
• Spark normally occurs prior TDC on the compression stroke.Spark normally occurs prior TDC on the compression stroke.
• Normal ignition timing can cause an eng. to kick back.Normal ignition timing can cause an eng. to kick back.
• To prevent kick back, magneto use a second set of retard breaker points toTo prevent kick back, magneto use a second set of retard breaker points to
retard the spark during eng. starting.retard the spark during eng. starting.
• Retard mean to delayed the spark until its reaches TDC on the compressionRetard mean to delayed the spark until its reaches TDC on the compression
stroke.stroke.
• Retard ignition, make it easy to start but does not increase the voltage.Retard ignition, make it easy to start but does not increase the voltage.
• All magneto incorporate ignition booster or auxiliary ignition unit.All magneto incorporate ignition booster or auxiliary ignition unit.
• Ignition booster includes:- the impulse coupling, induction vibration, showerIgnition booster includes:- the impulse coupling, induction vibration, shower
of spark ignition system and booster magneto.of spark ignition system and booster magneto.

Impulse couplingImpulse coupling
 Widely used on auxiliary ignition system.Widely used on auxiliary ignition system.
 Is a small spring-loaded device.Is a small spring-loaded device.
 Provide a magneto with momentary high rotational speed and aProvide a magneto with momentary high rotational speed and a
retarded spark.retarded spark.
 Uses a spring loaded mechanical linkage that wound up by theUses a spring loaded mechanical linkage that wound up by the
magneto drive gear and released to increase rotational speed.magneto drive gear and released to increase rotational speed.
 Impulse coupling consist of:Impulse coupling consist of:
- Impulse coupling body.- Impulse coupling body.
- Flyweight mounted to a cam.- Flyweight mounted to a cam.
- Coiled spring- Coiled spring..

• Cam assembly of an impulse coupling is keyed to the magneto shaft.Cam assembly of an impulse coupling is keyed to the magneto shaft.
• Impulse coupling body rotates with the engine.Impulse coupling body rotates with the engine.
• Coiled spring inside the impulse coupling links the cam assembly and body together.Coiled spring inside the impulse coupling links the cam assembly and body together.
• Eng. turn, flyweights on the impulse coupling contact stop pins on the magnetoEng. turn, flyweights on the impulse coupling contact stop pins on the magneto
housing.housing.
• Stop pins stop magneto shaft rotation, eng. continues to rotate and wind up theStop pins stop magneto shaft rotation, eng. continues to rotate and wind up the
impulse coupling spring.impulse coupling spring.
• Coupling body contact trigger ramp on the flyweight forcing the flyweight to off theCoupling body contact trigger ramp on the flyweight forcing the flyweight to off the
stop pins.stop pins.
• This releases accelerates the magneto speed and produce high voltage, retarded spark.This releases accelerates the magneto speed and produce high voltage, retarded spark.

• Produces high voltage spark during startingProduces high voltage spark during starting
process.process.
• Once eng. started, magneto speed fast enough toOnce eng. started, magneto speed fast enough to
produce high voltage on its own.produce high voltage on its own.
• Centrifugal force pulls the heel of the flyweightsCentrifugal force pulls the heel of the flyweights
outward so no longer contact the stop pins.outward so no longer contact the stop pins.
• Impulse coupling disabled.Impulse coupling disabled.
• Sparks back to their normal advanced timing.Sparks back to their normal advanced timing.

Induction vibrationInduction vibration
 Supply pulsating DC to primary winding.Supply pulsating DC to primary winding.
 Pulsating current flows will be induced into the secondary winding.Pulsating current flows will be induced into the secondary winding.
 The faster the pulsating DC, the greater the current induced for starting.The faster the pulsating DC, the greater the current induced for starting.
 The frequency of the pulsating DC is determined by the induction vibrator.The frequency of the pulsating DC is determined by the induction vibrator.
 Vibrator operates when switch is “engage or start” to produced pulsating current.Vibrator operates when switch is “engage or start” to produced pulsating current.
 Magneto breaker closed current flow to the ground.Magneto breaker closed current flow to the ground.
 When open pulsating DC flows in and produce high voltage pulses to distributor thenWhen open pulsating DC flows in and produce high voltage pulses to distributor then
to spark plug.to spark plug.
 Frequency of pulses produced by the vibrator coil allow multiple sparks to beFrequency of pulses produced by the vibrator coil allow multiple sparks to be
produced at a spark as long as point remain open.produced at a spark as long as point remain open.
 As the points close, pulsating current routed to ground.As the points close, pulsating current routed to ground.
 This process is repeated each time breaker points open and pulsating current flows toThis process is repeated each time breaker points open and pulsating current flows to
the primary winding.the primary winding.
 As engine started the starter switch is disengaged stop the current flow to theAs engine started the starter switch is disengaged stop the current flow to the
induction vibrator.induction vibrator.

Shower of sparksShower of sparks
• Works the same as the induction vibrator system.Works the same as the induction vibrator system.
• Except its has a set of retard breaker point to provide retardExcept its has a set of retard breaker point to provide retard
spark when engine is cranked.spark when engine is cranked.
• Located in the left magneto together with advance points.Located in the left magneto together with advance points.
• Start position, a relay in the starting vibrator grounds the rightStart position, a relay in the starting vibrator grounds the right
magneto and provides pulsating to the left magneto.magneto and provides pulsating to the left magneto.
• Both retard and advance are grounded, points must be open toBoth retard and advance are grounded, points must be open to
allow current flow to the primary winding.allow current flow to the primary winding.
• Engine started switch to both position, battery power is removedEngine started switch to both position, battery power is removed
from the starting vibrator.from the starting vibrator.
• Right magneto ungrounded and retard point disconnected.Right magneto ungrounded and retard point disconnected.
• Both mag. operate normally to provide advance spark.Both mag. operate normally to provide advance spark.
• Components used are solid state no maintenance required.Components used are solid state no maintenance required.
• If fails removed and replaced.If fails removed and replaced.

Booster MagnetosBooster Magnetos
 Not in use on modern a/c.Not in use on modern a/c.
 Consist of separate magneto andConsist of separate magneto and
located in the cockpit.located in the cockpit.
 Hand operated by pilot duringHand operated by pilot during
starting.starting.
 Voltage generated by boosterVoltage generated by booster
magneto supplied to a specialmagneto supplied to a special
distributor that directed a spark todistributor that directed a spark to
the cylinder just behind the one thatthe cylinder just behind the one that
normally fired by the engine driven.normally fired by the engine driven.
 If firing order is 1-3-5-7-9-2-4-6-8.If firing order is 1-3-5-7-9-2-4-6-8.
 Booster magneto supplies spark toBooster magneto supplies spark to
cylinder no. 1 when eng. drivencylinder no. 1 when eng. driven
mag. to fire cylinder no. 3.mag. to fire cylinder no. 3.
 This retards the spark for ignition.This retards the spark for ignition.

Ignition SwitchIgnition Switch
• To provide means of controlling when ignition is switch “ON”To provide means of controlling when ignition is switch “ON”
and operating.and operating.
• Ignition located in the cockpit, operated by pilot.Ignition located in the cockpit, operated by pilot.
• SwitchSwitch “OFF”“OFF” contactcontact closedclosed.. “ON”“ON” contactcontact openopen..
• Ignition switch is wired in parallel with the breaker point.Ignition switch is wired in parallel with the breaker point.
• ““OFF”OFF” position – contactposition – contact closedclosed to ground the circuit. Preventto ground the circuit. Prevent
magnetic field in the primary winding from collapsing andmagnetic field in the primary winding from collapsing and
induced to secondary winding.induced to secondary winding.
• ““ON”ON” position – contactposition – contact openopen. Breaker point interrupt primary. Breaker point interrupt primary
current flow to produce the pulsating current to create spark.current flow to produce the pulsating current to create spark.
• Ignition switch lead which connects the switch and the primaryIgnition switch lead which connects the switch and the primary
circuit referred to ascircuit referred to as P-leadP-lead..
• P-lead consists of several strands of cooper wire are shielded toP-lead consists of several strands of cooper wire are shielded to
help reduce radio interference.help reduce radio interference.

Ignition switch conts.Ignition switch conts.
 Switch controls both magnetos.Switch controls both magnetos.
 Has four position:Has four position: “OFF”, “LEFT”, “RIGHT”, and “BOTH”.“OFF”, “LEFT”, “RIGHT”, and “BOTH”.
 ““OFF”OFF” position, P-lead on both mag. are grounded.position, P-lead on both mag. are grounded.
 ““LEFT”LEFT” position, left mag. operates and right mag. grounded.position, left mag. operates and right mag. grounded.
 ““RIGHT”RIGHT” position, right mag. operates and left mag. grounded.position, right mag. operates and left mag. grounded.
 ““BOTH”BOTH” both mag. operate simultaneously to produce spark.both mag. operate simultaneously to produce spark.
 Operational check should follow manufacturers checklist.Operational check should follow manufacturers checklist.
 Start the engine then accelerate to 1,500 and 1,700 rpm.Start the engine then accelerate to 1,500 and 1,700 rpm.
 Engine stabilizes, place ignition switch from both to :Engine stabilizes, place ignition switch from both to :
- Left :- right mag grounded – slight drop in eng. rpm.- Left :- right mag grounded – slight drop in eng. rpm.
- Both :- rpm should return to normal value.- Both :- rpm should return to normal value.
- Right :- left mag. grounded – slight drop in eng. rpm.- Right :- left mag. grounded – slight drop in eng. rpm.
- Return back to Both position when completed.- Return back to Both position when completed.
 - Engine drop to zero while operating either left or right a short exists- Engine drop to zero while operating either left or right a short exists
between mag. and ignition switch.between mag. and ignition switch.
 FromFrom BothBoth toto OffOff momentarily eng. should quit because mag. are grounded.momentarily eng. should quit because mag. are grounded.
 If eng. fail to cease P-lead or faulty ignition switch. Stabilize eng. at grd. idle beforeIf eng. fail to cease P-lead or faulty ignition switch. Stabilize eng. at grd. idle before
shutdown.shutdown.

Magneto OverhaulMagneto Overhaul
• Most magnetos are reliable and trouble free.Most magnetos are reliable and trouble free.
• Remain on an engine until the engine isRemain on an engine until the engine is
overhaul.overhaul.
• Often sent to manufacture or certified repairOften sent to manufacture or certified repair
station for overhaul.station for overhaul.
• Any overhaul to be carried out strictly refer toAny overhaul to be carried out strictly refer to
manufacture’s overhaul manual.manufacture’s overhaul manual.

Disassembly and CleaningDisassembly and Cleaning
• Disassemble and clean a magneto as outlined inDisassemble and clean a magneto as outlined in
manufacturer’s maintenance manual.manufacturer’s maintenance manual.
• All components should handle with care to avoidAll components should handle with care to avoid
damage.damage.
• Soft ironSoft iron keeperkeeper should be placed across the poles ofshould be placed across the poles of
magnet to retain it’s magnetism.magnet to retain it’s magnetism.
• Cleaning magneto components only with approvedCleaning magneto components only with approved
solvents and cleaning methods.solvents and cleaning methods.
• Most manufacturers specify that acetone to used forMost manufacturers specify that acetone to used for
cleaning grease and carbon track from capacitor andcleaning grease and carbon track from capacitor and
coil.coil.

InspectionInspection
• When overhaul the magneto certain parts or componentsWhen overhaul the magneto certain parts or components
required to be replaced.required to be replaced.
• Components normally replaced during overhaul:Components normally replaced during overhaul:
- Breaker point.- Breaker point.
- Capacitor.- Capacitor.
- Bearing.- Bearing.
- Distributor block and rotor.- Distributor block and rotor.
- Lock nuts.- Lock nuts.
- Gaskets.- Gaskets.
- Cotter pins.- Cotter pins.
- Self-locking nuts or screw.- Self-locking nuts or screw.
- Oil seals.- Oil seals.
• Before discarding the items its good to check/inspect them forBefore discarding the items its good to check/inspect them for
evidence of malfunction and excessive wear.evidence of malfunction and excessive wear.

Magnet CaseMagnet Case
• Inspect magneto housing for crack.Inspect magneto housing for crack.
• Other area that prone for crack are:Other area that prone for crack are:
• - Mounting flange.- Mounting flange.
• - Bearing surface.- Bearing surface.
• - Area around threaded holes.- Area around threaded holes.
• - Mating surface.- Mating surface.
• Any crack found on the component replace the item.Any crack found on the component replace the item.
• Sign of pitting or corrosion. (light corrosion – remove it, ifSign of pitting or corrosion. (light corrosion – remove it, if
excessive replaced).excessive replaced).
• To prevent corrosion, mag. cases have one or more drains and aTo prevent corrosion, mag. cases have one or more drains and a
vent.vent.
• Drain prevent condensation in the mag. case.Drain prevent condensation in the mag. case.
• Vent allows the corrosive gases to escape and helps to cool theVent allows the corrosive gases to escape and helps to cool the
magneto.magneto.

Rotating MagnetRotating Magnet
Both magnet and magneto shaft to be inspectedBoth magnet and magneto shaft to be inspected
for physical damage and wear.for physical damage and wear.
Magneto shaft required dimensionally check toMagneto shaft required dimensionally check to
determine it is within serviceable limit.determine it is within serviceable limit.
Magnet to be check using magnetometer orMagnet to be check using magnetometer or
gauss meter for it strength.gauss meter for it strength.
If lost its magnetism, it may be remagnetized byIf lost its magnetism, it may be remagnetized by
special equipment.special equipment.

Gear assemblies and BearingGear assemblies and Bearing
●● Distributor drive gear, cleaned and inspect for:Distributor drive gear, cleaned and inspect for:
- excessive wear.- excessive wear.
- cracks.- cracks.
- broken teeth.- broken teeth.
●● Excessive backlash or play in the distributor drive gear is causeExcessive backlash or play in the distributor drive gear is cause
for rejection.for rejection.
●● Magneto shaft bearings and races to be replaced during overhaul.Magneto shaft bearings and races to be replaced during overhaul.
●● Some manufacture’s permit its to be reuse again but must beSome manufacture’s permit its to be reuse again but must be
inspect and service as prescribed by the manufacturer.inspect and service as prescribed by the manufacturer.

Magneto coilMagneto coil
 Inspect insulating material for crack and burn mark.Inspect insulating material for crack and burn mark.
 Check for coil lead for general condition and security.Check for coil lead for general condition and security.
 Check for continuity and resistance in each winding.Check for continuity and resistance in each winding.
 Can be done by ohmmeter or multimeter.Can be done by ohmmeter or multimeter.
Breaker assembly.Breaker assembly.
 Breaker point subjected to intense wear.Breaker point subjected to intense wear.
 Replace with a new set whenever a magneto is overhaul.Replace with a new set whenever a magneto is overhaul.
 Before discarding, check the breaker points.Before discarding, check the breaker points.
 If points are badly pitted, it may indicate the capacitor is notIf points are badly pitted, it may indicate the capacitor is not
functioning.functioning.

DistributorDistributor
• Distributor can be reuse, if permits byDistributor can be reuse, if permits by
the manufacturer.the manufacturer.
• Must inspect the distributor block andMust inspect the distributor block and
rotor for crack, carbon tracks, soot androtor for crack, carbon tracks, soot and
sign of arcing.sign of arcing.
• Check for excessive play by insert aCheck for excessive play by insert a
specific size of drill between each of thespecific size of drill between each of the
gear teeth.gear teeth.
• Should fits nicely.Should fits nicely.
• No sign of cracking or arcing, the blockNo sign of cracking or arcing, the block
should be tested with high tensionshould be tested with high tension
harness tester for any leakage or shorts.harness tester for any leakage or shorts.
• For reassembly coat it with wax toFor reassembly coat it with wax to
prevent arcing as per manufactureprevent arcing as per manufacture
instruction.instruction.

CamCam
• Made of either a solid piece of metal or phenolicMade of either a solid piece of metal or phenolic
compound.compound.
• For metal cam can be reused if dimensionallyFor metal cam can be reused if dimensionally
checked within limit.checked within limit.
• Phenolic cam to be discard and replace with newPhenolic cam to be discard and replace with new
cam.cam.

Assembly and Internal timingAssembly and Internal timing
• Magneto components that had been cleaned and inspected canMagneto components that had been cleaned and inspected can
be reassemble IAW manufacture’s instruction/manual.be reassemble IAW manufacture’s instruction/manual.
• And also internal timing process as manufacturer’s timingAnd also internal timing process as manufacturer’s timing
instructions.instructions.
• Mag. internal timing performed during assembly and carried outMag. internal timing performed during assembly and carried out
in bay and bench check.in bay and bench check.
• ForFor Bendix magnetoBendix magneto, case halves are assembled then carried, case halves are assembled then carried
out internal timing cx.out internal timing cx.
• But forBut for Slick magnetoSlick magneto carried out internal timing first then onlycarried out internal timing first then only
put the case halves together.put the case halves together.
• Do not put on force during assemble the case halves together,Do not put on force during assemble the case halves together,
you could damage the distributor rotor.you could damage the distributor rotor.

Bench testingBench testing
 All magneto that has been reassembled and internally time should be tested.All magneto that has been reassembled and internally time should be tested.
 Test carried out on the magneto test stand.Test carried out on the magneto test stand.
 Test stand includes a variable-speed drive motor, tachometer and spark rack.Test stand includes a variable-speed drive motor, tachometer and spark rack.
 Mount a magneto on the stand.Mount a magneto on the stand.
 Check the gap on the spark rack. (slightly bigger than spark plug – lessCheck the gap on the spark rack. (slightly bigger than spark plug – less
resistance than in the cylinder)resistance than in the cylinder)
 If gap too wide, excessive voltage build up could damage the coil andIf gap too wide, excessive voltage build up could damage the coil and
distributor.distributor.
 Connect all the high-tension harness.Connect all the high-tension harness.
 Verify the direction of the rotation before engaging the motor.Verify the direction of the rotation before engaging the motor.
 From slow speed to high speed – there should have sparks on the spark rack.From slow speed to high speed – there should have sparks on the spark rack.
 If poor performance could be improper timing, weak capacitor or weakIf poor performance could be improper timing, weak capacitor or weak
magnet.magnet.

Magneto to Engine timingMagneto to Engine timing
 Performed when installed on the engine.Performed when installed on the engine.
 When timing two magnetos to an engine, its could be eitherWhen timing two magnetos to an engine, its could be either
synchronized or staggered ignition.synchronized or staggered ignition.
 Synchronized ignition timingSynchronized ignition timing::
- Magnetos are timed to fire both spark plugs at the- Magnetos are timed to fire both spark plugs at the
same time.same time.
 Staggered ignition timing:Staggered ignition timing:
- Requires the two plugs to fired at slightly difference- Requires the two plugs to fired at slightly difference
time.time.
- Spark plug nearest to cylinder’s exhaust fired first.- Spark plug nearest to cylinder’s exhaust fired first.
- Reason – Fuel/air mixture become diluted by the exhaust gases- Reason – Fuel/air mixture become diluted by the exhaust gases
and tends to burn more slowly.and tends to burn more slowly.

Flange-Mounted magnetoFlange-Mounted magneto
• Special tool required are:Special tool required are:
- Time-rite indicator.- Time-rite indicator.
- Time light (synchronizer).- Time light (synchronizer).
• Set piston no.1 cylinder to TDC on compression strokeSet piston no.1 cylinder to TDC on compression stroke
(with spark plug removed).(with spark plug removed).
• Attach the magneto to the mounting and secured.Attach the magneto to the mounting and secured.
• Attach timing light to each magneto.Attach timing light to each magneto.
• Rotate magneto until timing light just come on andRotate magneto until timing light just come on and
tighten bolts (ensure propeller not move).tighten bolts (ensure propeller not move).
• To verify the timing, rotate propeller opposite directionTo verify the timing, rotate propeller opposite direction
timing light off and turn prop forward again light cometiming light off and turn prop forward again light come
on again.on again.

Base-Mount magnetosBase-Mount magnetos
• Found on the radial engine and coupled to the engine accessoryFound on the radial engine and coupled to the engine accessory
drive with vernier coupling.drive with vernier coupling.
• Special toothed coupling with slotted rubber disk sandwichedSpecial toothed coupling with slotted rubber disk sandwiched
between two gears with different number of tooth.between two gears with different number of tooth.
• Adjustment carried out by disconnecting the coupling and rotateAdjustment carried out by disconnecting the coupling and rotate
the rubber disk to the necessary number of slots.the rubber disk to the necessary number of slots.
Operational checkOperational check
 After reinstall the magnetos an operational check to be done.After reinstall the magnetos an operational check to be done.
 Ensure P-lead is connected and also spark plug leads.Ensure P-lead is connected and also spark plug leads.
 To verify the entire ignition system is properly function, theTo verify the entire ignition system is properly function, the
operational check have to be carried out.operational check have to be carried out.
 Run the engine using manufacturer stating procedures.Run the engine using manufacturer stating procedures.

Magneto MaintenanceMagneto Maintenance
 Common maintenance need to be performed are;Common maintenance need to be performed are;
- Inspection and examination of the magneto.- Inspection and examination of the magneto.
- Integrity and security of the case.- Integrity and security of the case.
- Condition of the points.- Condition of the points.
- Capacitor and distributor.- Capacitor and distributor.
- Magneto to engine timing.- Magneto to engine timing.
- Operational check.- Operational check.
 Magneto case.Magneto case.
- Check for crack, replace if crack.- Check for crack, replace if crack.
- Corrosion – removed and painted.- Corrosion – removed and painted.
- Pitting exist badly – replace the case..- Pitting exist badly – replace the case..
- Vent clear from obstruction if clog trap nitric acid gases will- Vent clear from obstruction if clog trap nitric acid gases will
corrode the internal part of the magneto.corrode the internal part of the magneto.

Breaker pointBreaker point
• To check points P-lead to be disconnected.To check points P-lead to be disconnected.
• Bear in mind that magneto is life (hot)Bear in mind that magneto is life (hot)
regardless of the ignition switch position.regardless of the ignition switch position.
• New breaker pointNew breaker point (A)(A) have a smooth, flathave a smooth, flat
surface with a dull gray, sandblasted orsurface with a dull gray, sandblasted or
frosted appearance.frosted appearance.
• After few hours of operationAfter few hours of operation (B),(B), slightlyslightly
wavy appearance.wavy appearance.
• Excessive metal transfer the pointExcessive metal transfer the point (C)(C)
become pitted or coarse grained.become pitted or coarse grained.
• Replace breaker point.Replace breaker point.
• Excessive wear can shift the internal timing.Excessive wear can shift the internal timing.
Point worn out, open early and advance thePoint worn out, open early and advance the
spark and open for longer period andspark and open for longer period and
decrease in spark intensity.decrease in spark intensity.

Breaker assemblyBreaker assembly
• Oil presence on the point no effect to the operation.Oil presence on the point no effect to the operation.
• It will attract contaminating metal and dirt particles that can lead to burningIt will attract contaminating metal and dirt particles that can lead to burning
and pitting.and pitting.
• Remove oil from the point by insert apiece of clean hard cardboard betweenRemove oil from the point by insert apiece of clean hard cardboard between
the two contacts.the two contacts.
• Never slide the cardboard, particles could leave behind and contaminate theNever slide the cardboard, particles could leave behind and contaminate the
point.point.
• Check the spring using a small spring scale.Check the spring using a small spring scale.
• Attach to the spring arm and carefully pulling the contact points apart.Attach to the spring arm and carefully pulling the contact points apart.
• Open not more thanOpen not more than 1/16 in1/16 in. to prevent damage to the spring.. to prevent damage to the spring.
• Spring tension below limit could cause the points float or bounce at highSpring tension below limit could cause the points float or bounce at high
speeds and will loss of spark energy.speeds and will loss of spark energy.
• Breaker cam checked for wear and damage such as pitting or distortion.Breaker cam checked for wear and damage such as pitting or distortion.
• Excessive wear could lead to point open late and retard the ignition.Excessive wear could lead to point open late and retard the ignition.
• Open at shorter time and decreases the spark intensity.Open at shorter time and decreases the spark intensity.

CapacitorCapacitor
• Excessive point wear caused by defect capacitor.Excessive point wear caused by defect capacitor.
• Checked capacitor using condenser tester.Checked capacitor using condenser tester.
• These tester use AC voltage to check capacitor’s capacity andThese tester use AC voltage to check capacitor’s capacity and
DC voltage to check for electrical leakage.DC voltage to check for electrical leakage.
• Capacitor capacitance value too low breaker point will burnedCapacitor capacitance value too low breaker point will burned
and pitted.and pitted.
DistributorDistributor
 Distributor block and rotor check for crack, carbon tracks ,sootDistributor block and rotor check for crack, carbon tracks ,soot
and sign of arcing.and sign of arcing.
 Crack block and rotor provides low resistance path to grd. forCrack block and rotor provides low resistance path to grd. for
secondary voltage.secondary voltage.
 Small crack requires replacement.Small crack requires replacement.

SealsSeals
• Presence of oil in a magneto indicates oil seal fail.Presence of oil in a magneto indicates oil seal fail.
• Oil conductors electricity, anytime oil is found in a magneto,Oil conductors electricity, anytime oil is found in a magneto,
must removed and disassembled, cleaned and inspected.must removed and disassembled, cleaned and inspected.
• Change seal as required.Change seal as required.
TimingTiming
 Magneto to eng. timing should be checked as part of a 100 hrsMagneto to eng. timing should be checked as part of a 100 hrs
and annual inspection.and annual inspection.
 If unsatisfactory during operational check, mag. to eng. orIf unsatisfactory during operational check, mag. to eng. or
internal timing to be carried out.internal timing to be carried out.
 Anytime breaker assembly is removed for cleaning or replace,Anytime breaker assembly is removed for cleaning or replace,
internal timing must be readjusted.internal timing must be readjusted.
 Also magneto to eng. timing.Also magneto to eng. timing.

Engine AnalyzerEngine Analyzer
 Monitored engine performance to aid in diagnosing eng.Monitored engine performance to aid in diagnosing eng.
problem.problem.
 System tracked ignition system performance and eng. vibration.System tracked ignition system performance and eng. vibration.
 Displayed them on the an adaptation of a laboratoryDisplayed them on the an adaptation of a laboratory
oscilloscope.oscilloscope.
 Unit can be portable and permanently installed.Unit can be portable and permanently installed.
 Today , CHT, exhaust gas temp. gauges primarily used asToday , CHT, exhaust gas temp. gauges primarily used as
indirect indicators of ignition system.indirect indicators of ignition system.

Ignition HarnessIgnition Harness
• Ignition system to be efficient.Ignition system to be efficient.
• Must be delivered to the spark with minimalMust be delivered to the spark with minimal
loss.loss.
• PurposePurpose to deliver high voltage to spark plugto deliver high voltage to spark plug
through low resistance elect. path and keepsthrough low resistance elect. path and keeps
leakage to a minimum.leakage to a minimum.
• Harness consist of 4, 6, or 8 individual ignitionHarness consist of 4, 6, or 8 individual ignition
leads.leads.
• One end to a receptacle on a magneto and theOne end to a receptacle on a magneto and the
other end to spark plug.other end to spark plug.

Harness ConstructionHarness Construction
• Conductor use in spark plug lead isConductor use in spark plug lead is
stranded wire or single coiled.stranded wire or single coiled.
• Encased in one or two layers ofEncased in one or two layers of
rubber or silicone insulation.rubber or silicone insulation.
• Covered with braided metal shield.Covered with braided metal shield.
• Insulation prevents current leakage.Insulation prevents current leakage.
• Shielding to reduce radio frequency byShielding to reduce radio frequency by
collect and channels high frequencycollect and channels high frequency
electromagnetic to ground.electromagnetic to ground.
• Protect shielding from chaffing andProtect shielding from chaffing and
moisture, the shielding is impregnatedmoisture, the shielding is impregnated
with a silicone material.with a silicone material.

Ignition HarnessIgnition Harness

Harness constructionHarness construction
• Two different size used in a/c ignitionTwo different size used in a/c ignition
harness, 5mm and 7mm.harness, 5mm and 7mm.
• 5mm commonly used and 7mm for5mm commonly used and 7mm for
older a/c.older a/c.
• Modern ignition leads ends can fit 5/8-Modern ignition leads ends can fit 5/8-
24 shielded spark plug or ¾- 20 all24 shielded spark plug or ¾- 20 all
weather spark plug.weather spark plug.
• (A)(A) Ignition leads are terminated withIgnition leads are terminated with
straight terminals or bent to facilitatestraight terminals or bent to facilitate
installation.installation.
• Sharp bend causes stress and weakSharp bend causes stress and weak
point.point.
• (B)(B) 7mm lead require large bend radius,7mm lead require large bend radius,
angled terminal are available with 70°,angled terminal are available with 70°,
90°,110 and 135° elbows.90°,110 and 135° elbows.
• (C)(C) 5mm straight terminal can be bend5mm straight terminal can be bend
if bracket is installed to hold at a safeif bracket is installed to hold at a safe
bend radius.bend radius.

• Terminal ends on ignition leads consists of a silicone rubberTerminal ends on ignition leads consists of a silicone rubber
nose that slip into a spark plug body.nose that slip into a spark plug body.
• Referred asReferred as all weatherall weather terminal, prevent water from enteringterminal, prevent water from entering
on top of spark plug body.on top of spark plug body.
• Terminals are crimped onto an ignition lead and the coiled wireTerminals are crimped onto an ignition lead and the coiled wire
screws over the end of the terminal.screws over the end of the terminal.
• Replaced if become damage.Replaced if become damage.

• Older terminals with a phenolic or ceramicOlder terminals with a phenolic or ceramic
insulator tube referred to as ainsulator tube referred to as a cigarettecigarette..
• Terminal contains coiled spring extends beyondTerminal contains coiled spring extends beyond
the end of the insulator tube.the end of the insulator tube.
• Provide positive electrical contact betweenProvide positive electrical contact between
ignition lead and spark plug.ignition lead and spark plug.

• Cigarette-type terminal ignition lead insulator have to be cut at the back of itCigarette-type terminal ignition lead insulator have to be cut at the back of it
to allow wire to protrude.to allow wire to protrude.
• Conductor wire is then fanned out to secure the wire to the cigarette andConductor wire is then fanned out to secure the wire to the cigarette and
provide good contact.provide good contact.
• Magneto end leads utilize crimp on type connector.Magneto end leads utilize crimp on type connector.
• Exact type of connector depend on types used.Exact type of connector depend on types used.
• Another method, connect ignition leads to a distributor block with cableAnother method, connect ignition leads to a distributor block with cable
piercing screws.piercing screws.
• All installation to ensure braided wire to be secured at both ends. (grounded).All installation to ensure braided wire to be secured at both ends. (grounded).
• If not, radio interference could occur when engine running.If not, radio interference could occur when engine running.

MaintenanceMaintenance
 Maintenance consists of repairing, replacing terminal ends orMaintenance consists of repairing, replacing terminal ends or
chaffed lead.chaffed lead.
 Information of replacement procedure and tools used asInformation of replacement procedure and tools used as
manufacturer instruction.manufacturer instruction.
 Replacement can be made by single harness or entire set.Replacement can be made by single harness or entire set.
 If come in set, the harnesses are precut to the proper length.If come in set, the harnesses are precut to the proper length.
 Pay close attention to wire markings that indicate the distributorPay close attention to wire markings that indicate the distributor
terminal to spark plug.terminal to spark plug.
 Eg. 1T indicate a lead cut to length for top spark plug for no. 1Eg. 1T indicate a lead cut to length for top spark plug for no. 1
cylinder.cylinder.
 Routed and secure all lead around the exhaust and not interfereRouted and secure all lead around the exhaust and not interfere
with flight control.with flight control.
 Ensure shielding properly grounded, added second layer ofEnsure shielding properly grounded, added second layer of
shielding as required.shielding as required.

Installation tools.Installation tools.

TestingTesting
• Anytime a conductor carries high voltageAnytime a conductor carries high voltage
energy and is installed near a conductiveenergy and is installed near a conductive
mass.mass.
• The insulation around the conductor isThe insulation around the conductor is
exposed to what is known asexposed to what is known as high voltagehigh voltage
corona.corona.
• Repeated exposure can cause dielectricRepeated exposure can cause dielectric
strength of the insulation to breakdown.strength of the insulation to breakdown.
• Increase the possibility of arcing.Increase the possibility of arcing.
• To detect breakdown in the insulator have toTo detect breakdown in the insulator have to
use high tension harness tester.use high tension harness tester.
• Tester applies 15,000 volts DC to the leadTester applies 15,000 volts DC to the lead
and then uses aand then uses a micro-ammetermicro-ammeter to detectto detect
the leakage.the leakage.
• Another type use is light indicator or byAnother type use is light indicator or by
inability spark to jump an air gap in theinability spark to jump an air gap in the
tester.tester.

Spark PlugSpark Plug
 The end result, spark that ignite theThe end result, spark that ignite the
fuel/air mixture in the cylinder.fuel/air mixture in the cylinder.
 The construction and operation of a sparkThe construction and operation of a spark
plug is simple but demands placed onplug is simple but demands placed on
ignition systems are high.ignition systems are high.
 If eng. operate at 2,100 rpm, approx. 17If eng. operate at 2,100 rpm, approx. 17
separate ignition events occur per second.separate ignition events occur per second.
 About 20,000 volt spark jumps the air gap.About 20,000 volt spark jumps the air gap.
 Its must be able to operate in temp. ofIts must be able to operate in temp. of
3,000°F or higher and pressure of 2,0003,000°F or higher and pressure of 2,000
psi.psi.

ConstructionConstruction
• Most spark plugs are similarMost spark plugs are similar
in appearance.in appearance.
• Difference do exist amongDifference do exist among
spark plug types.spark plug types.
• Engine manufacturers specifyEngine manufacturers specify
the type of spark plugs inthe type of spark plugs in
used.used.
• Consists of three major parts;Consists of three major parts;
- Metal shell- Metal shell
- Ceramic insulator- Ceramic insulator
- Electrode assembly- Electrode assembly

Construction conts.Construction conts.
• Metal shellMetal shell::
- Provides support for the internal component.- Provides support for the internal component.
- Provides an electrical path to grd. for braided shield- Provides an electrical path to grd. for braided shield
of the ignition lead.of the ignition lead.
- Shells are threaded at both ends.- Shells are threaded at both ends.
- One end allow an ignition lead to be attached to- One end allow an ignition lead to be attached to
spark plug, referred to as terminal or shield threadsspark plug, referred to as terminal or shield threads
- Opposite end to be screwed into a cylinder.- Opposite end to be screwed into a cylinder.
- To facilitate the installation and removal a spark plug- To facilitate the installation and removal a spark plug
a hex or six-sided nut is cast on the metal shell.a hex or six-sided nut is cast on the metal shell.

• Ceramic insulatorCeramic insulator::
- Prevent high voltage current flowing through a plug- Prevent high voltage current flowing through a plug
from arching to ground.from arching to ground.
- Insulator consists of two sections;- Insulator consists of two sections;
▪▪ One section extends from tip of the centerOne section extends from tip of the center
electrode up to the terminal contact.electrode up to the terminal contact.
▪▪ The other section from top of spark plug barrel andThe other section from top of spark plug barrel and
extends downward to overlap with the first insulatorextends downward to overlap with the first insulator
section.section.
▪▪ Nickel gaskets between plug shell and insulatorNickel gaskets between plug shell and insulator
prevent escape of high pressure from the cylinder.prevent escape of high pressure from the cylinder.

▪▪ Electrode assemblyElectrode assembly::
Consist of a terminal contact, resistor, glass seal, center electrodeConsist of a terminal contact, resistor, glass seal, center electrode
and outer electrode.and outer electrode.
- Terminal contact – where the ignition lead makes contact with- Terminal contact – where the ignition lead makes contact with
the spark plug.the spark plug.
- The opposite end of the thermal contact is a small resistor.- The opposite end of the thermal contact is a small resistor.
- Resistor is to prevent capacitance afterfiring.- Resistor is to prevent capacitance afterfiring.
-- Capacitance afterfiringCapacitance afterfiring is the process which electrical energyis the process which electrical energy
is induced into the ignition shielding when current flowsis induced into the ignition shielding when current flows
through an ignition lead.through an ignition lead.
- Once the electrical potential in the shielding builds, stored- Once the electrical potential in the shielding builds, stored
energy is released as surge across the air gap of the spark plug.energy is released as surge across the air gap of the spark plug.
- This lengthens the spark duration and accelerates wear of the- This lengthens the spark duration and accelerates wear of the
plug electrodes.plug electrodes.
- By inserting a resistor in a spark plug, the stored voltage in the- By inserting a resistor in a spark plug, the stored voltage in the
shielding is dissipated so it can not jump across the plug gap.shielding is dissipated so it can not jump across the plug gap.
- Resistor has a value of 1,500 ohms.- Resistor has a value of 1,500 ohms.

Conts.Conts.
- Material used to construct the center and outer electrodes varies- Material used to construct the center and outer electrodes varies
depending on the types of electrode used.depending on the types of electrode used.
-- Massive-electrodeMassive-electrode spark plug, the outer or grd. electrodesspark plug, the outer or grd. electrodes
made of nickel alloy and center electrode from nickel-cladmade of nickel alloy and center electrode from nickel-clad
copper.copper.
-- Fine wire electrodeFine wire electrode plug, the grd. electrode made of platinumplug, the grd. electrode made of platinum
or iridium and center electrode from silver.or iridium and center electrode from silver.
- The ground and center electrode on spark plug are separated by- The ground and center electrode on spark plug are separated by
an air gap of a specific width.an air gap of a specific width.
- The size of the air gap determines the amount of resistance a- The size of the air gap determines the amount of resistance a
spark must overcome before it can jump the gap.spark must overcome before it can jump the gap.
- If size of an air gap not adjusted properly, the intensity of the- If size of an air gap not adjusted properly, the intensity of the
spark produced will also be incorrect.spark produced will also be incorrect.

Shell Thread ClassificationShell Thread Classification
 Spark plugs are classified according to theSpark plugs are classified according to the
size of the shell threads that screw into thesize of the shell threads that screw into the
cylinder.cylinder.
 Plug threads are either 14 mm or 18 mm.Plug threads are either 14 mm or 18 mm.
 Most modern a/c use 18 mm spark plug.Most modern a/c use 18 mm spark plug.
 The terminal come in two sizes; eitherThe terminal come in two sizes; either ⅝⅝ inin
– 24 thread or ¾ in – 20 thread.– 24 thread or ¾ in – 20 thread.
 Both sizes are used in a/c but ¾ in – 20 isBoth sizes are used in a/c but ¾ in – 20 is
the size of choice.the size of choice.
 ¾ in – 20 thread is referred as all-weather¾ in – 20 thread is referred as all-weather
spark plug.spark plug.
 All-weather spark plug the ceramic insulatorAll-weather spark plug the ceramic insulator
does not extend to the top of the plug shell.does not extend to the top of the plug shell.
 This leave a room for the silicone grommetThis leave a room for the silicone grommet
to form a watertight seal at the terminal.to form a watertight seal at the terminal.

Spark Plug ReachSpark Plug Reach
• ReachReach defined as the liner distance from the shell gasket seat todefined as the liner distance from the shell gasket seat to
the end of the shell threads or shell skirt.the end of the shell threads or shell skirt.
• Spark plug are available eitherSpark plug are available either long reachlong reach oror short reachshort reach..
• On 14mm plugs, long reach dimension is 12.7mm or ½ in.; shortOn 14mm plugs, long reach dimension is 12.7mm or ½ in.; short
reach is 9.53mm or ⅜ in.reach is 9.53mm or ⅜ in.
• On 18mm plugs, long reach dimension is 20.64mm or 13/16 in.;On 18mm plugs, long reach dimension is 20.64mm or 13/16 in.;
short reach is 12.7mm or ½ in.short reach is 12.7mm or ½ in.
• Spark plug installed in an engine, the end of the threads shouldSpark plug installed in an engine, the end of the threads should
bebe flushflush with the cylinder head’s inside wall.with the cylinder head’s inside wall.
• Install a spark plug with theInstall a spark plug with the wrong reachwrong reach, it will either, it will either extendextend
beyondbeyond oror recessedrecessed in the cylinder.in the cylinder.

• For example:-For example:-
▪▪ If long reach spark plug isIf long reach spark plug is
installed where a short reach pluginstalled where a short reach plug
is required;is required; (A)(A)
- end thread of the plug will be- end thread of the plug will be
exposed to the heat ofexposed to the heat of
combustion.combustion.
- exposed thread will susceptible- exposed thread will susceptible
to carbon buildup, make itto carbon buildup, make it
difficult to remove.difficult to remove.
▪▪ If short reach plug is used inIf short reach plug is used in
place of long reach plug;place of long reach plug; (B)(B)
- thread in the cylinder head will- thread in the cylinder head will
exposed to combustion gases andexposed to combustion gases and
possible damage.possible damage.

Heat RangeHeat Range
▪▪ Refers to the spark plug ability to conduct heatRefers to the spark plug ability to conduct heat
away from its firing tip to the cylinder head.away from its firing tip to the cylinder head.
▪▪ Classified as:Classified as:
- “Hot”, “normal” or “cold” plugs depending- “Hot”, “normal” or “cold” plugs depending
how well they transfer heat.how well they transfer heat.
▪▪ Primary factor in determining a plug’s heatPrimary factor in determining a plug’s heat
range is the length of the nose core.range is the length of the nose core.
▪▪ (A)(A) Cold plugsCold plugs – short nose core – large– short nose core – large
contact area between the ceramic insulatorcontact area between the ceramic insulator
and plug shell.and plug shell.
- Large contact area allows heat to conduct- Large contact area allows heat to conduct
readily to the cylinder head.readily to the cylinder head.
▪▪ (B)(B) Hot plugsHot plugs – long nose – provide little– long nose – provide little
contact area for heat to dissipate.contact area for heat to dissipate.

Heat RangeHeat Range
• All a/c engines are certified to use spark plug with a specific heatAll a/c engines are certified to use spark plug with a specific heat
range.range.
• General rule, high compression engine operates at highGeneral rule, high compression engine operates at high
temperature and use cold spark plug.temperature and use cold spark plug.
• Lower compression engine operates relatively low temperatureLower compression engine operates relatively low temperature
and use hot spark plug.and use hot spark plug.
• If hot spark plug use on engine required cold spark plug theIf hot spark plug use on engine required cold spark plug the
hotter operating temperature of the plug could lead tohotter operating temperature of the plug could lead to
preignition or engine run-on.preignition or engine run-on.
• Cold spark plug is installed in a cold running engine, plugCold spark plug is installed in a cold running engine, plug
become fouled with unburned carbon and lead deposits.become fouled with unburned carbon and lead deposits.
• Some circumstances require to use spark plug that may not be inSome circumstances require to use spark plug that may not be in
the recommended heat range.the recommended heat range.
- e.g. :- Engine run on 80 octane avgas, required a hotter plug- e.g. :- Engine run on 80 octane avgas, required a hotter plug
when use 100LL avgas due to higher lead contain.when use 100LL avgas due to higher lead contain.
- Higher lead level could cause lead fouling in the cooler- Higher lead level could cause lead fouling in the cooler

ServicingServicing
• Manufacturers recommend the removal of sparkManufacturers recommend the removal of spark
plug for inspection and servicing at regularplug for inspection and servicing at regular
intervals.intervals.
• 100 hrs inspection.100 hrs inspection.
• Intermittent engine running cause by defectIntermittent engine running cause by defect
plug.plug.
• Badly fouled plug no ignition will occur.Badly fouled plug no ignition will occur.

RemovalRemoval
▪▪ Before remove a set of spark plugs, you must first remove theBefore remove a set of spark plugs, you must first remove the
ignition lead.ignition lead.
▪▪ When removing, best hold the ignition lead with one hand andWhen removing, best hold the ignition lead with one hand and
then loosen the terminal nut.then loosen the terminal nut.
▪▪ Once the terminal nut fully back off, pull the terminal endOnce the terminal nut fully back off, pull the terminal end
straight out of the plug.straight out of the plug.
▪▪ Tilting a lead terminal can crack or damage the insulator.Tilting a lead terminal can crack or damage the insulator.
▪▪ Remove the spark plug with deep socket.Remove the spark plug with deep socket.
▪▪ Ensure the socket is squarely over the plug hex and loosen it.Ensure the socket is squarely over the plug hex and loosen it.
▪▪ Tilting the socket could damage the plug ceramic insulator.Tilting the socket could damage the plug ceramic insulator.
▪▪ Plug is removed and placed in a tray.Plug is removed and placed in a tray.
▪▪ Easy to identify from which cylinder number and position (top orEasy to identify from which cylinder number and position (top or
bottom).bottom).

Visual InspectionVisual Inspection
• Visual inspection of spark plugs reveals about theVisual inspection of spark plugs reveals about the
efficiency of an engine.efficiency of an engine.
• If plug covered with a dull brown deposit and littleIf plug covered with a dull brown deposit and little
buildup in the firing cavity, normal combustion.buildup in the firing cavity, normal combustion.
• Firing cavity is filled with hard, bead-like deposits,Firing cavity is filled with hard, bead-like deposits,
excessive lead fouling. Fouling must be investigatedexcessive lead fouling. Fouling must be investigated
and corrected.and corrected.
- Causes include improper fuel vaporization, low- Causes include improper fuel vaporization, low
cylinder head temperature or improper plug heatcylinder head temperature or improper plug heat
range.range.
- Should install plug with a hotter heat range.- Should install plug with a hotter heat range.
• Covered with a soft black sooty deposit, indicate aCovered with a soft black sooty deposit, indicate a
problem with carbon fouling.problem with carbon fouling.
- Cause of rich mixture or leak primer.- Cause of rich mixture or leak primer.
- If deposit appear on the exhaust stack also cause by- If deposit appear on the exhaust stack also cause by
excessively rich mixture.excessively rich mixture.

Visual inspectionVisual inspection
• Oil fouling is another type of contamination found on sparkOil fouling is another type of contamination found on spark
plug.plug.
- cause by broken or worn piston ring and worn valve guides.- cause by broken or worn piston ring and worn valve guides.
- appears as blackened, slippery coating on a plug’s electrodes.- appears as blackened, slippery coating on a plug’s electrodes.
- serve enough an engine have to be removed and repair.- serve enough an engine have to be removed and repair.
• Existence of hard glaze on plug, indicates that sand was ingestedExistence of hard glaze on plug, indicates that sand was ingested
into the engine.into the engine.
• In chamber some of the silicates in sand melt with the heat ofIn chamber some of the silicates in sand melt with the heat of
combustion.combustion.
- as molten silicates cool, they form a glass-like coating on plug.- as molten silicates cool, they form a glass-like coating on plug.
- silicon glaze is non-conductive at low temperature.- silicon glaze is non-conductive at low temperature.
- high temperature, glaze become conductive and lead to spark- high temperature, glaze become conductive and lead to spark
plug misfiring.plug misfiring.
- sand ingestion is the result of poor filter and induction system- sand ingestion is the result of poor filter and induction system
leak.leak.

Visual inspectionVisual inspection
• If the electrodes on a spark plug areIf the electrodes on a spark plug are
worn to approx. half their original size,worn to approx. half their original size,
it should be replaced.it should be replaced.
• Excessive wear can distort the shape ofExcessive wear can distort the shape of
both the center and ground electrodes.both the center and ground electrodes.
• Abnormal wear on plug’s electrodes isAbnormal wear on plug’s electrodes is
an indication of fuel meteringan indication of fuel metering
problems, cause by;problems, cause by;
- excessively lean mixture.- excessively lean mixture.
- induction air leak.- induction air leak.
- partially clogged fuel nozzle.- partially clogged fuel nozzle.
• Beside check for plug wear, shouldBeside check for plug wear, should
examine the ceramic insulator for crack.examine the ceramic insulator for crack.
• If crack found replaced with new plug.If crack found replaced with new plug.
• If plug dropped on hard surface,If plug dropped on hard surface,
automatically discarded.automatically discarded.

CleaningCleaning
• Clean spark plug with approvedClean spark plug with approved
safety solvent to remove oil, grease,safety solvent to remove oil, grease,
and other soft deposit from theand other soft deposit from the
plug’s exterior and firing cavity.plug’s exterior and firing cavity.
• Once degreased, dried withOnce degreased, dried with
compressed air.compressed air.
• Lead and carbon deposits removedLead and carbon deposits removed
with a vibrating cleaning tool.with a vibrating cleaning tool.
• - use proper cutting blade.- use proper cutting blade.
• - hold spark plug directly over the- hold spark plug directly over the
blade.blade.
• - slight back and forth motion over- slight back and forth motion over
the blade will chip away the leadthe blade will chip away the lead
deposits.deposits.

CleaningCleaning
• To complete the cleaning process on the plug, an abrasive gritTo complete the cleaning process on the plug, an abrasive grit
blasting cleaner can be used.blasting cleaner can be used.
• Adhere to the manufacturer’s instruction concerning grit typeAdhere to the manufacturer’s instruction concerning grit type
and air pressure.and air pressure.
• Silica abrasive is not recommended because it can contribute toSilica abrasive is not recommended because it can contribute to
silica fouling.silica fouling.
• When using grit blast cleaner;When using grit blast cleaner;
- move plug in circular motion.- move plug in circular motion.
- limit to few seconds only.- limit to few seconds only.
- this help to prevent excessive erosion especially on fine-wire- this help to prevent excessive erosion especially on fine-wire
• After blasting, blow out all traces of the grit with clean air.After blasting, blow out all traces of the grit with clean air.
• If used wet-blast method, dry plug in an oven to avoid rusting.If used wet-blast method, dry plug in an oven to avoid rusting.
• When clean and dry, inspect them with light and magnifyingWhen clean and dry, inspect them with light and magnifying
glass.glass.
• Clean plug thread on both end with a steel brush or soft bristlesClean plug thread on both end with a steel brush or soft bristles
to remove any carbon or corrosion.to remove any carbon or corrosion.

GappingGapping
• Gap between the center and ground electrode to be checked and adjusted as required.Gap between the center and ground electrode to be checked and adjusted as required.
• Gap of 0.16, do cx. with round wire gauge of 0.15 and 0.19 in. (go or no go)Gap of 0.16, do cx. with round wire gauge of 0.15 and 0.19 in. (go or no go)
• If gap too big, the ground electrode may be forced inward to reduce the gap.If gap too big, the ground electrode may be forced inward to reduce the gap.
• Use proper tool and manufacturer’s instructions to prevent damage to nose ceramic orUse proper tool and manufacturer’s instructions to prevent damage to nose ceramic or
electrode.electrode.
• Adjusting gap on a massive-electrodeAdjusting gap on a massive-electrode
plug using a special gapping tools.plug using a special gapping tools. → ►→ ►
• - ground and center electrode must be- ground and center electrode must be
remain parallel.remain parallel.
• - plug must be clamp to the tool.- plug must be clamp to the tool.
• - ground electrode is moved inward using- ground electrode is moved inward using
a movable arm or threaded adjusting arm.a movable arm or threaded adjusting arm.
• - adjusting slowly,- adjusting slowly,
prevent closing gap too much.prevent closing gap too much.
• - any attempt to enlarge a gap on a- any attempt to enlarge a gap on a
massive-electrode plug may cause damagemassive-electrode plug may cause damage
to insulator or electrodeto insulator or electrode

GappingGapping
• Do not leave the wire gauge between theDo not leave the wire gauge between the
two electrodes.two electrodes.
• If left behind will damage the insulatorIf left behind will damage the insulator
when apply load during gap adjustment.when apply load during gap adjustment.
• Fine-wire spark plug with electrode ofFine-wire spark plug with electrode of
platinum and iridium are extremely brittleplatinum and iridium are extremely brittle
and easily broken, handle with care.and easily broken, handle with care.
• Avoid closing the gap too much.Avoid closing the gap too much.
TestingTesting
▪▪ Once a spark plug is cleaned and gapped,Once a spark plug is cleaned and gapped,
it should be tested.it should be tested.
▪▪ Use special testing equipment, provideUse special testing equipment, provide
voltage to fire the plug in rapidvoltage to fire the plug in rapid
succession under pressure.succession under pressure.

InstallationInstallation
• When installing plugs you should rotate them from where theWhen installing plugs you should rotate them from where the
plugs were originally installed.plugs were originally installed.
• This promotes even plug wear and extends plug service life.This promotes even plug wear and extends plug service life.
(metal transfer from one electrode to another).(metal transfer from one electrode to another).
PolarityPolarity
▪▪ Each time rotating magnet passes the natural position, polarity ofEach time rotating magnet passes the natural position, polarity of
current changes.current changes.
▪▪ Spark produced by a magneto alternate in polarity.Spark produced by a magneto alternate in polarity.
▪▪ Engine with an even number of cylinder, each spark plug firesEngine with an even number of cylinder, each spark plug fires
with same polarity every time.with same polarity every time.
▪▪ If no. 1 cylinder spark jump from ctr. to grd. electrode.If no. 1 cylinder spark jump from ctr. to grd. electrode.
▪▪ And next cylinder in firing order no.4 , spark will jump from grd.And next cylinder in firing order no.4 , spark will jump from grd.
to ctr. electrode.to ctr. electrode.
▪▪ When the polarity of sparks on a plug do not change, oneWhen the polarity of sparks on a plug do not change, one
electrode looses metal relative to the other one.electrode looses metal relative to the other one.

PolarityPolarity
• Plug fire positively, the groundPlug fire positively, the ground
electrode looses more than theelectrode looses more than the
center electrode.center electrode.
• When plug fire negatively, theWhen plug fire negatively, the
center electrode wears more thancenter electrode wears more than
the ground electrode.the ground electrode.
• Spark plug rotation will balance theSpark plug rotation will balance the
electrode wear and increase theelectrode wear and increase the
service life of a plug.service life of a plug.
• Swap the plugs from top to bottom.Swap the plugs from top to bottom.
• The reason is lead and otherThe reason is lead and other
impurities produced duringimpurities produced during
combustion process tend tocombustion process tend to
precipitate to the lower plug.precipitate to the lower plug.
• Help equalize plug wear.Help equalize plug wear.

PolarityPolarity
• Before installing the plug, appliedBefore installing the plug, applied
anti-seize compound to the shellanti-seize compound to the shell
threads.threads.
• Applied the correct type suppliedApplied the correct type supplied
by spark plug manufacturers.by spark plug manufacturers.
• Apply on the second thread fromApply on the second thread from
the firing end.the firing end.
• Never put at the firing end, it couldNever put at the firing end, it could
run down over the electrode.run down over the electrode.
• Replace gasket whenever install theReplace gasket whenever install the
plug, once harden gasket loses itsplug, once harden gasket loses its
ability to seal.ability to seal.

Reciprocating engine starting systemReciprocating engine starting system
• Early day of aviation to start a/c engine by handEarly day of aviation to start a/c engine by hand
propping.propping.
• Problem in cold weather, thick oil hard to turn.Problem in cold weather, thick oil hard to turn.
• Engine got larger make more difficult and dangerous.Engine got larger make more difficult and dangerous.
Types of Starting SystemTypes of Starting System
• Inertia StarterInertia Starter
• Direct-Cranking Starters (Electrical Starter)Direct-Cranking Starters (Electrical Starter)
a.a. Small engine startersSmall engine starters
b. Large engine startersb. Large engine starters

Inertia StarterInertia Starter
Inertia StarterInertia Starter
•Hand crank to spin flywheel through a step-upHand crank to spin flywheel through a step-up
gear drive assembly.gear drive assembly.
•When high speed, hand crank removed and theWhen high speed, hand crank removed and the
starter engage.starter engage.
•The kinetic energy of the spinning flywheel isThe kinetic energy of the spinning flywheel is
converted to mechanical energy to drive engineconverted to mechanical energy to drive engine
crankshaft.crankshaft.
•A torque overload clutch located between the
flywheel-ratchet jaws prevent damage to the
engine or starter when its first engaged.

Direct-cranking startersDirect-cranking starters
• Used electric motor to spin the flywheel for easierUsed electric motor to spin the flywheel for easier
engine starting. However hank cranking feature stillengine starting. However hank cranking feature still
applied if insufficient battery power.applied if insufficient battery power.
• This type widely used on all types of recip. engines.This type widely used on all types of recip. engines.
This provides instant and continual cranking whenThis provides instant and continual cranking when
energized.energized.
• This type used series wound dc motors to drive theThis type used series wound dc motors to drive the
starter.starter.
• This type is capable of producing a high starting torque.This type is capable of producing a high starting torque.

• Relatively constant voltageRelatively constant voltage
throughout a starting cycle.throughout a starting cycle.
• Drawing out very high current at the start ofDrawing out very high current at the start of
motor rotation.motor rotation.
• Do not contain fuses or circuit breakers becauseDo not contain fuses or circuit breakers because
it will tripped circuit breaker or blown fuse eachit will tripped circuit breaker or blown fuse each
time the engine started.time the engine started.

Small engine startersSmall engine starters
• Used small series engine would electric motor with small gear.Used small series engine would electric motor with small gear.
• Small gear meshes large gear and part of an over-running clutchSmall gear meshes large gear and part of an over-running clutch
and drive pinion or drive gear.and drive pinion or drive gear.
• Engaged by either a hand-pulled cable or a solenoid whichEngaged by either a hand-pulled cable or a solenoid which
engages a shift lever.engages a shift lever.
• Hand-pulled cable attached by cable /rod to tee-handle.Hand-pulled cable attached by cable /rod to tee-handle.
• Electrical switch activates a solenoid.Electrical switch activates a solenoid.
• When started over-running clutch spinning until tee-handle orWhen started over-running clutch spinning until tee-handle or
starter switch released and return spring pulls the pinion awaystarter switch released and return spring pulls the pinion away
from the starter gear.from the starter gear.

Small engine startersSmall engine starters

Another type of direct cranking used Bendix driveAnother type of direct cranking used Bendix drive
as used in automobile. Consist of :as used in automobile. Consist of :
• Drive spring.Drive spring.
• Drive pinion.Drive pinion.
• Drive shaft.Drive shaft.
• Helical splines.Helical splines.

OperationOperation
• When starter switch is closed the starter spins theWhen starter switch is closed the starter spins the
pinion through drive spring. The pinion movespinion through drive spring. The pinion moves
forward on the helical splines and engages theforward on the helical splines and engages the
teeth on the engine flywheel and turn the engine.teeth on the engine flywheel and turn the engine.
• When the engine started the flywheel gear spinWhen the engine started the flywheel gear spin
drive pinion faster than the starter motor.drive pinion faster than the starter motor.
• This forces the pinion back along the helicalThis forces the pinion back along the helical
splines until it engages from the flywheel.splines until it engages from the flywheel.

Bendix driveBendix drive
as used in automobileas used in automobile

Teledyne-continental starterTeledyne-continental starter
• Starter mounted on the side.Starter mounted on the side.
• Starter rotate the worm gear.Starter rotate the worm gear.
• Worm gear permanently meshed worm wheel.Worm gear permanently meshed worm wheel.
• Clutch spring attached to the worm wheel.Clutch spring attached to the worm wheel.
• Worm wheel rotate it tightens the spring around aWorm wheel rotate it tightens the spring around a
knurled drum on the engine’s starter shaft.knurled drum on the engine’s starter shaft.
• When gets tight enough, starter shaft begins to rotate.When gets tight enough, starter shaft begins to rotate.
• Shaft gear then rotate the crankshaft gear and rotate theShaft gear then rotate the crankshaft gear and rotate the
c/shaft.c/shaft.

Teledyne-continental starterTeledyne-continental starter

• As crankshaft spin faster then the starter gearAs crankshaft spin faster then the starter gear
shaft causing the clutch spring to release theshaft causing the clutch spring to release the
knurled and disengaged.knurled and disengaged.
• The generator drive pulley is mounted on theThe generator drive pulley is mounted on the
end serves as generator drive shaft.end serves as generator drive shaft.

Large engine startersLarge engine starters
• Required to turn over a high horsepower engineRequired to turn over a high horsepower engine
and therefore employed reduction gearand therefore employed reduction gear
assembly.assembly.
• Consisting automatic engaging and disengagingConsisting automatic engaging and disengaging
mechanism houses as a single unit.mechanism houses as a single unit.
• Reduction gear motor shaft converts motor’sReduction gear motor shaft converts motor’s
high speed low torque to low speed high torque.high speed low torque to low speed high torque.

Large engine startersLarge engine starters

• Motor’s pinion drives the intermediateMotor’s pinion drives the intermediate
countershaft assembly.countershaft assembly.
• And rotate the sun gear.And rotate the sun gear.
• Sun gear then rotate the planetary gears.Sun gear then rotate the planetary gears.
• Therefore engaging the starter jaw to the engine.Therefore engaging the starter jaw to the engine.
• When the engine has started the return springWhen the engine has started the return spring
push the starter jaw to the rear and disengagedpush the starter jaw to the rear and disengaged
the jaw from the engine.the jaw from the engine.

06 piston eng ignition

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