ETA 15D MK 3 AND ELITE - 5cc ENGINE BUILDS
Part nine - by Ramon Wilson
Part four - by Ramon Wilson

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First off for the cylinder heads was to part off some blanks and bore them. The Mk3 and Elites are blind bores with a slide fit over the liner. The Elite Mk2 had fins shrunk onto the liner so this was made a tad undersize and has a separate head. there was a spare liner left over from the Mk1&2 build so this was used as a plug gauge for the three and will have the fins shrunk on to it at a later stage before lapping.

Held on another freshly turned expanding mandrel the first three were faced off to length to a stop then the ODs finish turned.
The next op was to drill them through and counterbore the holes for the head bolts. It was found on the last engines that the drill tends to wander far less when drilling from solid than through precut fins plus it's much easier to debur the holes in the fins done this way.
The top angle was turned then the fins cut with a 2.3mm wide grooving tool ground from a FC3 cutter shank. Drilling and tapping for the comp screw was the last op.


The expanding mandrel was then reduced a thou or so by filing and polishing to accept the Mk2 fins and these were drilled through. Another grooving tool, this time 1mm wide was ground up and the fins gingerly cut, depth of cut on all heads was 5.1mm. Despite a bit of vibration with the interrupted cuts as it passed the drilled holes this thin tool held up well.

Last off was to make the head to suit.  A blank was set in the soft jaws and the base and a 1mm register to fit the fins turned before reversing and taking out the deep groove - another 'FC3' tool bit being ground up for this. The holes were drilled and counterbored and then the eight cooling holes drilled .....
It's been quite a while since this little gizmo was used but those holes (48 divs) in the chuck came into play on this op
The two parts for the Mk2 head .....
..... and all heads finished ready to fit


See part one here  part two  part three  part four  part five  part six  part seven  part eight 

part nine  part 10



 

January 19th-21st