distributor ignition

1. IGNITIONSYSTEMS
ost of us tend to ignore ignition
systems — they’re there and as
long as they’re not coughing,
spluttering or at worse dying by the side of
the road, we all tend to leave them be. But
early engines favour archaic points — and
most of us know how to get round their
idiosyncrasies and live with them. But it
needn’t be so
The problem is, when they’re new and
tight, points do work but give them 20-plus
years of use and the propensity for wear and
slop is huge. It’s then they become
unreliable. The answer is often electronic
replacement — by fitting a module in the
distributor, you can loose the points for
good. But there’s the first hurdle — we’re
forgetting about the wear! If you simply
whack in a magic box of tricks, you can still
be faced with unreliability simply because
the distributor itself is worn out.
Reconditioning is of course the answer,
so we visited H&H Ignition Solutions to
find out not only the basics of distributor-
based ignitions but how to improve them
beyond all measure.
It’s true most distributors are well and
truly obsolete — so much so it’s almost
impossible to find good, useable bodies on
which to build new units. The answer, as
always, they’re now copied in the Far East
— but they also need a rather large dose of
adapting and modification to work in classic
Ford applications.
H&H’s Lee Hull, Phil Hull and John
Morley guide us through the options,
which include their very trick-looking
billet-bodied, Bosch-based Pinto
distributors.
First though, we could do with finding
out some basics.
Modern cars may no longer use them, but the distributor is a vital part of
any standard or tuned classic engine. Here’s how to get the best from them.
DefinitiveGuide
M
Words and Photos Jon Hill
Contacts
H&HIgnitionSolutions
01384261500
www.h-h-
ignitionsolutions.co.uk
Info
CFTECH
October 2012 97
“MOSTOFUS
IGNOREIGNITION
SYSTEMS—UNTIL
THEYGOWRONG”

2. CFTECH
98 October 2012
“LATERFORD
ENGINESUSED
ABOSCH
DISTRIBUTOR
WHICHHAD
ELECTRONIC
IGNITION”
Distributor
History
KnowyourLucasfromyourBoschunits,
andwhyit’sbesttoavoidMotorcraftones.
POINTS
A mechanical contact
breaker system,which
switches the low tension
circuit to high tension so
the coil can generate the
massive voltage needed
to jump the spark plug
gap;igniting the fuel/
air mixture.
CAP
This carries the terminals for
the rotor arm to interact
with,to distribute the spark.
Make sure it’s on the right
way and not cracked,as it
will arc out.
he distributor used on almost every British car
from the ’50s onwards was Lucas-manufactured.
All of Lucas’ distributors were equipped with
centrifugal advance mechanisms with the addition of the
vacuum-advanced 25D coming slightly later being used
to aid economy and driveability in the lower rpm range.
Ford opted for the fitment of sidedraught carburettors
on some hot factory engines, and these engines would
have been fitted with a 23D4 — the ‘23’ denoting a
non-vacuum distributor .
Ford also developed their own distributor under the
Motorcraft brand.These are not liked anywhere near as
much as the Lucas or Bosch units.They tend to wear and
aren’t as adaptable.You are likely to find either of these
two units on a Kent engine.
Early Pinto and Essex engines also used Motorcraft
units but later engines are more likely to use a Bosch
distributor.These units tend to be specific to the engine
they were intended for — they aren’t as easy to modify
for other applications in the same way that a Lucas
25D4 is.
The main difference though is in electronics – Bosch
junked the points distributor in favour of Hall Effect and
magnetic-type ignition systems which switched the coil
via an ignition module. Sometimes this was remote-
mounted on an alloy heat sink or on some models
mounted on the distributor itself (something which H&H
now adopt for their billet-bodied distributors).
The ignition module — whether Hall Effect or
magnetic — is triggered by a pick-up and chopper wheel
assembly inside the distributor.
TheValencia engine in late Fiestas also used a similar
arrangement, which is a popular swap for the Crossflow,
though the advance curves aren’t necessarily correct.
This type of Bosch system is probably an intermediate
stage between points and full engine-managment,
distributorless ignition systems.These, of course, use
a crank sensor — typically mounted on the back of the
flywheel.
This gives engine positioning - inconjunction with
coil packs and wasted spark — operated by the ECU via
an EDIS unit.Very clever stuff but way too advanced for
this feature!
T
You need to view every distributor as
worn and in need of a rebuild – this H&H
can typically do for you for about £80.
It’s common for people to fit
electronic modules inside an old
distributor body, but they are prone to
wear, not just in the bearings but the
centrifugal advance weights itself.
However, these themselves don’t wear,
but the control springs can lose there
strength and advance too early.
In general you should only see
minimal play in the shaft when rocked
side to side — anything that you can
open the breaker gap by moving the
spindle is in need of a rebuild. Make
sure the advance characteristics are
correct for your engine, and pay
particular attention to the drive system
too — not all have the same helical
gears on the base of the shaft — other
makes use a drive dog (BL products in
particular).Therefore you need to be
sure your potential distributor suits
your application.Always fit a new rotor
arm, cap, points and condenser.
BUYINGSECOND-
HANDDISTRIBUTORS
SHAFT
Typically driven by the cam,
this mounts the system of
centrifugal weights.
October 2012 99
definitiveguide:classicignitionsystems

3. CFTECH
100 October 2012 October 2012 101
Sparkproduction
Howitworks
The Coil
The whole point of the ignition system is to
generate a fat spark to jump an air gap from
the spark plug’s central electrode to its earth;
requiring a minimum of 14,000Volts (14kV) to
do so.This of course ignites the compressed
fuel/air charge causing it to burn and force the
piston back down the bore.The timing of the
charge-lighting is critical to both good
performance and engine health,
First though, the actual spark production is
generated by the coil — basically, a
transformer containing two sets of windings
(and therefore circuits) wrapped round an Iron
core. However, the first one’s pretty critical to
the second.
This first is lightly packed and when
commonly induced by 12 volts, generates a
magnetic field bumping up the voltage.This is
controlled by a set time while contact breakers
are closed this is called the dwell angle and
allows the coil its maximum recharge time
between sparking. However, electronic
ignition is able to give variable dwell giving the
ultimate control of the HT coil for maximum
spark, but the longer it’s allowed to do this, the
greater voltage it sends to the second set of
greater-packed windings, which bumps it even
further to that massive voltage level.
To switch from the first circuit to that second
circuit — known as collapsing the field — is the
job of the contact breaker.Traditionally a
mechanical device which controls the dwell
angle, the points are located within the
distributor acting as a switch for the coil —
directing from the LowTension circuit to the
HighTension circuit. From there it travels via
the HT leads to the relevant spark plug directed
by the distributor.
Traditional coils have the windings housed
in oil and produce around 12-14 KV as long as
the distributor and its components are in
tip-top condition.
These work OK but can be improved with the
addition of a sports coil.These have modified
windings inside, which raise the output to
around 26-28 KV and improve the spark
integrity throught out the rev range. They
are still known as low voltage coils and
only work with points based
ignition and some aftermarket
ignition kits — although that
doesn’t mean they’re inferior.
The difference becomes
apparent when we switch to
electronic ignition, where a
different, higher-voltage coil
can be used since
there are no
points to burn out.
Electronic
Ignition
The problem with
traditional
systems is that,
like all systems,
they rely on a
distributor and
its components to
control the LT
circuit.
This signal is
called the dwell angle
which is controlled by
the points, and slop in the
points, adjustment, wear or any
other mechanical factor can have an obvious
effect on the latter circuit’s performance. So
one of the persistent quests of any ignition
system has been to make the result just that:
constant.
By replacing the contact breaker system
with an electronic switch, the result becomes
far more reliable.
There have been many ways to do this —
either by using manufacturers’ OE or H&H’s
full electronic systems that use magnetic or
Hall Effect systems in conjunction with an
ignition amplifier and high power HT coils, or
an aftermarket kit.
One of the first aftermarket kits was
Lumenition’s Optronic system, which used a
photocell, interfered by a passing ‘chopper’
blade which providing the switch.
Other units such as Pertronix, use passing
magnets to break the contact in a similar
fashion.These systems do predominantly still
use points-based, low-voltage HT coils.
The reliability factors are obvious but with
the fitment of electronic ignition, aftermarket
kits can be fitted with an uprated coil where as
full electronic ignition kits such as OE and
H&H’s top end kit can be fitted with the
ultimate in high power HT coils (the coil can
now be uprated further to an higher voltage),
resulting in a greater end voltage — from 40
KV and upwards.
These high voltage coils should not be used
with some of the aforementioned aftermarket
kits, and with points, it burns or melts them
very quickly.
Of course, further advances can be made in
this area too — it’s an option to bin the
traditional wet-coil, substituting it for a dry
type, only with full electronic ignition. H&H can
supply a very cost-effective dry coil producing
improved results using basically standard
OE components.
The Distributor
It’s pretty obvious what this unit does
— it distributes the HT voltage to
the spark plugs while
controlling the HT coil.
This is all triggered via a
shaft driven by the cam at
half engine speed —
there are four strokes
remember!
One of the most
important parts of the
distributor is seated way
down under the baseplate
— the centrifugal advance
mechanism.
This part is kept in check by
a spring and weight mechanism
which works during the increase
and decrease of the revs. Housed within
the distributor is a baseplate, which
traditionally carried the contact-breaker
system and condenser.
This baseplate moves via a vacuum, which
is a secondary advance mechanism that aids
economy and driveability when the engine is
at low rpm and vacuum pressure is present.
We’ve already touched on them, but there are
actually two methods of advance provision:
Vacuum Advance
A spring-loaded diaphragm within a circular
housing on the side of the distributor actuates
a lever when vacuum is present, which
physically rotates the base plate according to
the amount of vacuum the engine is
producing.
At idle, vacuum is often present if the
engine’s basically standard (with say a
twin-choke carburettor).When the vacuum
pressure is present the vacuum unit moves the
baseplate effectively advances the timing.
When sidedraught carburettors, or ’bike carbs
are fitted, this makes the vacuum redundant.
Mechanical advance
This is the part located below the baseplate
and controls the advance through the rev
range via springs and weights, which increase
and decrease the advance on a linear curve
through centrifugal force.
This can be radically different for all engine
types with standard units not really cutting it
with modified engines as they usually have
way too much advance. Lucas, Bosch and
Motorcraft used different configurations to
achieve this operation.
Ignition Timing and Advance
Within the four-stroke cycle of the combustion
engine, the piston travels fast up and down
the bore.
What’s needed is to ignite the intake charge at
its maximum point of compression, resulting in
the most efficient burn driving the piston back
down — making maximum power.Therefore we
need to accurately time when this occurs.
The problem is, the piston has momentum,
meaning it can be carried past the point of
compression, igniting the mixture too late
meaning the spark arrives too late caused by the
ignition timing being to retarded.
This can commonly be caused by seized or
lazy centrifugal advance mechanisms in
the distributor.
Although the same can happen too early — on
the up-stroke — if the distributor has too much
advance or premature advance. It can have
devastating effects from detonation leading to
holes in the pistons or burnt valves.
This is a more common on modified engine
where cams, compression, and heads have been
altered, and a standard, unmodified distributor is
being used.
Although it might seem like an explosion to us,
it’s actually burning at a rate dictated by the
amount of compression (established by both
static and dynamic compression ratio — CR), and
the fuel’s octane rating and air/fuel ratio (AFR) too.
Therefore, it is crucial that the distributor is
advancing at the right amount of degrees to send
the spark at the right time to coincide with the
piston reaching its optimum point.
Advance Curves
The level of ignition advance is different at
certain points in the engine’s rev range — at
idle, this is known as Static timing, and is
commonly set around 6-10-degrees BeforeTop
Dead Centre (BTDC).
Increases in engine speeds will alter the need
for more advance, and typically, this adds more
degrees thus advancing the spark. It really does
depend on plenty of factors — the state of tune,
volumetric efficiency; the list is endless and there
is no set level. It is in fact why we rolling road or
dyno our engines.
This then, is the basis for mapped ignition — but
we really are advancing too fast here...
BOSCH
We’ve already mentioned that Lucas
are one of the earliest points-type
distributors.The distributor body
was universal with internals and
drive dogs differing greatly between
different car manufacturers.
However core units are now scarce,
so replacement units are now
manufactured in the Far East.The
problem is,they’re likely to be based
on Land Rover units with way too
much advance — as much as 40
degrees.And as we’ve already
mentioned,wrong advance means
broken engines!Conversion to
electronic is pretty straight forward
now — the aftermarket electronic
conversion kits virtually drop
straight onto the baseplate and
coupled with a suitable coil,and a
distributor in optimum condition,
provide a simple reliable solution to
an old problem.
Similar to the Lucas scenario,
bodies are again scarce but H&H
have a solution in an adaptable
hybrid body.This is manufactured in
the UK from billet aluminium —
although the shaft is a reclaimed
unit,therefore they still need
your Bosch distributor on an
exchange basis.
The company uses a similar
mounting system to the Bosch CVH
method,which fits a plastic-cased
amplifier module onto the side of
the unit;therefore,eliminating the
need for complex wiring.Indeed
there are simply three wires — two
to the coil and one to ground.
These are original equipment
(OE) parts,which aren’t prone to
failure given the testing and
research put in by the manufacturer.
TYPESOF
DISTRIBUTOR
LUCAS25D4&23D4

4. IgnitionTiming
Lee and Phil Hull (uncle and
nephew) set up H&H Ignition
Solutions in 2003 after spending
their previous working lives at one
of the biggest distributor
remanufacturing companies in the
world, Delco Remy.
Not surprisingly, as mainstream
manufacturer’s ignition systems
moved more and more to
distributorless igntion, the two Hs
saw a gap in the market to look after
more traditional systems.The third
member of H&H, John Morley was
also a veteran of the same
company but he’d preceded their
leaving to concentrate on
traditional systems within the
Jaguar restoration field.
John’s role is as the expert in the
more conventional and early
ignition systems since H&H don’t
concentrate on just the Blue Oval
— they have the ability to do
everything.
As we’ve already discussed,
H&H’s product range is now
envious — producing some
gorgeous new distributors for
virtually every application. Phone
them and you’ll be speaking to Lee
— then you’ll discover their
knowledge is vast!
ENGINE TIMINGFIGURES
1500 Pre-Crossflow, twin 40s, Fast Road cam 10-12 degrees Static, 30-34-degrees total
1700 Crossflow, twin 40s, Fast Road cam 10-12 Static 30-34-degrees total
2-litre Pinto, twin 45s, Fast Road cam 10-12 Static 30-34-degrees total
NA Cosworth YB, twin 48s, NA-spec cams 16-20 Static, 30-34 degrees total- depending on spec
1600 CVH, twin 40s, Fast Road cam 10-12 Static 30-34-degrees total
ABOUTH&HIGNITIONSOLUTIONS
definitiveguide:classicignitionsystems
102 October 2012
Itisalmostimpossibletobespecificinthisareasincenotwoenginesareeffectivelyalike,
butreckononthesebasictimingfigurestogetyougoing:
1Removingthe
vacuum
advanceona
standardengine
improvesthe
performance
Only if you’re
running twin
sidedraughts or
carbs with erratic
idle vacuum — just
eliminating the
vacuum advance
doesn’t turn your
engine into a
performer, it’s often
the reverse
2Standard
distributors
are fine for
tuned engines
No. More than likely
they’ll have
incorrect advance
chracteristics and
this can lead to
broken engines.
Rebuild and
recalibrate the
distributor to your
engine’s needs
3Points were fine
back in the day,
why not now?
Just because
something was fine
40-years ago
doesn’t mean you
can disregard all the
technology that’s
since been applied
— remember the
‘will it start’
syndrome?
You don’t get that
with electronics
4Cheap,
internet
specials are great!
They’re cheap for a
reason!A properly-
built distributor will
have the right
advance curve
— plenty of specials
have way too
much advance
5Points can be
fixed by the side
of the road
They can if you
have the bits! But
you’re more likely
to be fixing them
by the side of the
road too...
MYTHS