Reverse Engineering a vintage motorcycle cylinder head

1. Billet Machined
Cylinder Head
Aswin Cmohan Supervised By,
MSc. Automotive Engineering Mr. Geoffrey Booth

2. Project aims and objective
▪ To reverse engineer an existing legacy component with a view of
recreating it using an alternative material and modern
manufacturing technology.
▪ Interrogate the component in order to obtain a geometrical data set
▪ Create a model using an industry standard software package.
▪ Verify and analyse the model.
▪ Create the toolpaths to produce the component giving due
consideration to appropriate sequencing, work holdings and
fixturing.
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3. AJS R6 CYLINDER HEAD
▪ The component to be reverse
engineered was a 1930 model AJS
R6 motorcycle cylinder head.
▪ The motorcycle had a twin port 350
cc engine.
▪ In an internal combustion engine the
cylinder head sits above the cylinder
on top of the engine block where it
closes the top to form the
combustion chamber.
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4. Visual Inspection
▪ To obtain accurate
dimensions, the component to
be measured should be clean
and not have any uneven
surfaces.
▪ One of the exhaust port was
damaged and the other was
capped off.
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Combustion Chamber

5. Data Acquisition
▪ First principle measurement process
using callipers, gauge blocks and
dial gauge.
▪ Surface table, parallels and dial
gauges were used to measure the
distance between the holes.
▪ Difficult to obtain the angles of the
exhaust and inlet port.
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6. Co-ordinate Measuring Machine (CMM)
CMM measuring the ports CMM measuring the combustion chamber
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7. CAD model
▪ The component was modelled using
CATIA-V5.
▪ Generative shape design and part
workbenches were used.
▪ Using the coordinates from the CMM
the required planes and points were
created.
▪ The model consists of two bodies
one for the fins and others includes
the port and combustion chamber.
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8. Design Changes
▪ Change of material
▪ Inlet port angle
▪ Spark plug size
▪ Heat dissipation fins.
▪ Exhaust port
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9. Change of material
▪ The material was changed from cast iron to an aluminium alloy.
▪ Hypoeutectic alloys are preferred as the silicon content is low.
▪ Aluminium has a high thermal conductivity compared to iron.
▪ Heat transfer coefficient is high.
▪ The aluminium alloy has to be heat treated to increase it tensile and fatigue
strength as the cylinder head works at high temperatures.
▪ The 333.0 (T6), 319.0 (T5) and 356.0 (T6) alloys are preferred due to their high
strength, rigidity and low silicon content.
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10. Inlet port angle
▪ The inlet port flow was improved to make it higher and straighter which is better
for peak power.
▪ The increase in the downdraught angle is limited as the clearance between the
inlet valve guide spring seating surface and the inlet port was small.
▪ The height of the inlet port and its length was increased by 10mm and 14 mm
respectively.
▪ The inlet port face angle was changed by 6 degrees.
▪ Diameter of the actuator spring seating surface was reduced to 30 mm and raised
by 3 mm.
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11. Computational Fluid Dynamics
Gas flow in the original inlet port Gas Flow in the modified inlet port.
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12. Spark Plug
▪ The diameter of the spark plug hole was 16 mm and used most of the face in the
combustion chamber.
▪ A flat seat type plug of diameter 10mm was selected.
▪ The small diameter increases the face inside the combustion chamber and can
also help to increase the heat transfer ratio.
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13. Heat dissipation fins and exhaust port
▪ Heat dissipation fins are used to increase the heat transfer rate.
▪ Effective cooling of an engine increases its engine life and performance.
▪ The cylinder head generates a large amount of heat and the cylinder walls should
not heat up the air before compression but also not cool down the gas at the
chamber.
▪ The heat can cause engine knocking which can damage the engine.
▪ Additional fins were added on to the cylinder head.
▪ The exhaust port’s external diameter was increased to accommodate space for
threads. A flange will be used to connect the exhaust port and the exhaust.
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14. Component Prototype
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15. Delcam Powermill
▪ The toolpaths were created using Delcam Powermill after importing the CAD file.
▪ The tools and tool holder was modelled in Delcam.
▪ Due to the complex design of the cylinder head, there were possibilities for the
tool holder to collide with the workpiece.
▪ Automatic collision check was activated in Delcam to ensure the tool holder does
not collide with the workpiece.
▪ A clearance of 0.5mm was set for both shank and the holder.
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16. Operations List
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▪ The operation strategies were
developed on how the billet will be
machined taking into consideration
work holdings and fixturing.
▪ The depth of the vice was measured
to be 50 mm. This helped determine
how much material should be left
over on the billet.
▪ The billet is aligned with the length,
width and height aligned to the X, Y
and Z axis of the CNC respectively.
Fig: Aluminium billet fixed on the vice

17. Operation 1 : Model Area Clearance
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▪ The operation was carried out with a
2.5mm step over and 20 mm step
down.
▪ The tool started to make chatter
noises and was halted.
▪ The step over was reduced from 2.5
mm to 2.0 mm which in turn reduced
the machining vibration.
▪ The entire cycle was approximately
60 hours.
Fig: Billet after completion of first operation

18. Operation 2 : Drilling Holes
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▪ The four holes were drilled and
counter bored.
▪ Peck drilling was carried out to
ensure the cut material doesn’t get
caught in between.
▪ The edges were machined off to
create a reference point which can
be clocked off for the subsequent
operations.
Fig: Billet after second operation

19. Operation 3 : Inlet Valve Guide Hole
▪ An adjustable angle plate will be
used to align the valve spring
seating surface perpendicular to the
Z axis of the CNC.
▪ The workpiece can be bolted on to
the adjustable angle plate and
rotated by 45 degrees in the X
direction.
▪ The edge reference and the circular
feature of the seating surface can be
clocked off to pick up the position.
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20. Operation 4 : Exhaust Valve Guide Hole
▪ The workpiece will be on the
adjustable angle plate after the third
operation.
▪ The workpiece will have to be
rotated by 45 degrees to make the Z
axis perpendicular to the exhaust
valve guide hole.
▪ The edge reference and the circular
feature of the seating surface can be
clocked off to pick up the position.
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21. Operation 5 : Spark Plug Hole.
▪ The spark plug will be drilled with
diameter of 10mm.
▪ Spark plug should be rotated by 45
degrees in the Y direction.
▪ The spark plug face should be
perpendicular to the Z axis.
▪ The spark plug hole should also be
threaded with pitch of 2mm and
length of 19 mm.
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22. Operation 6 : Removal of additional material
▪ The additional material used to hold the workpiece for certain operations can be
removed so that the combustion chamber can be machined.
▪ The edge references will be machined off and the four holes will now remain as
the reference points.
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23. Operation 7 : Combustion Chamber
▪ The diameter of the combustion chamber is 35 mm.
▪ The work piece will have to be laid on its back.
▪ Dowel pins are inserted into the four holes and be fixed on the CNC machines.
▪ Work piece should be clamped on both ends to hold it firmly in place.
▪ Ensure small step overs and step downs to get a better surface finish.
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24. Operation 8 : Model area clearance
▪ The clamps will be removed from the ends and placed over the combustion
chamber.
▪ Rest of the area is to be machined to remove the additional materials.
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25. Operation 9 : Machining the exhaust port
▪ Diameter of the exhaust port is 42.75
mm and they are aligned with two
critical angles.
▪ The cylinder head can be mounted
onto an adjustable angle plate with
an angle of 30.5 degrees in the Y
axis and 16.5 degrees in the X axis.
▪ This will align the tool to be
perpendicular to the exhaust ports,
and the exhaust port faces can be
used to clock off to obtain the
coordinates of the workpiece.
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26. Operation 10 : Machining the Intake port
▪ The intake port is at an angle of 15
degrees in the y axis and 4 degrees
in the x axis.
▪ The cylinder head can be bolted on
to an angular plate and adjusted
accordingly to align the workpiece
axes to the CNC axes.
▪ Automatic tool collision check is
recommended for these operations
as there is risk of the tool colliding
with the ports.
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27. Results
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28. Conclusion and Recommendations
▪ While machining the subsequent operations maintain the step overs at 2 mm, if it
goes above that the tool starts to vibrate which can also cause tool failure.
▪ Ensure the inlet and exhaust guide holes are machined deep enough so that it
can be picked up after the combustion chamber is machined in order to work on
the valve seats.
▪ A 2-Axis Trunnion Rotary Table can be set up in the 3-Axis system and can assist
in machining the subsequent operations without using angle plates or other tools
which can cause human errors affecting the accuracy of the cylinder head.
▪ Side lock tool holders are recommended for all the operations as they are more
stable than the collet types. The diameter of the side lock tools are also smaller
than the collet types which can prevent tool collision.
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29. THANK YOU
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