ETA 15D MK 3 AND ELITE - 5cc ENGINE BUILDS
Part 12+1  by Ramon Wilson
Part four - by Ramon Wilson
This is the block used to machine the crank webs.

The block was made from some extremely tough cast iron - a redundant twenty ton press bedplate. It has three V-grooves ground in and plenty of tapped holes for clamping screws.

It was much easier to align the centre line of the pin to that of the shaft than when held in the vice.
....and then mill either side to stops.
The liners are made from free cutting En1a which is a good combination with a cast iron piston. Bored the blanks to size first using the expanding mandrel made for the previous ones as a plug gauge then roughed the outer surfaces in the chuck before finishing the outer surfaces to the bore on the same mandrel.

Below: finished ready for milling the transfer and exhaust ports.

Cutting the porting in these liners is not a difficult operation but one that has to be done with a degree of accuracy if the timing is to remain as designed. The original liners were quite 'high tec' in their day - for model aircraft engines that is - in that they were investment cast steel and had the transfer ports cast in. Close examination of the Mk1 & 2 originals showed the tops of the transfer ports to be flat and square to the bore whereas most other engines of the day having angled ports being drilled or milled giving an elipse form inside the liner.  I filed the Mk 1 & 2 ports to a gauge but it occurred doing these that providing the holes were correctly located filing could be done until the inked up port just showed an indication of ink. The ports were made a bit larger as per the liner in the Elite that I was loaned. You will notice some slight difference in them - that is by choice, just to see if there is any performance difference.

First off was to mill the passages...

...then set the milling attachment at 35degrees and plunge cut the ports with a 3mm FC3 cutter. The position of this was established by CAD and ‘datumed’ off the lower surface of the exhaust flange which is the datum face for the timing for both ports. The liner was moved radially to widen the cut to match the passages by engaging back gear and applying radial motion by turning the main drive pulley by hand - there's a surprising amount of control doing it like that.
The cut outs were done at the same time as these would be used to align the liner to the rotary table for the next op....
....which was to cut the exhaust ports using a cutter made for the Mks1 & 2.
All finished ready for lapping. The one with the fins on is for the Elite Mk2 which had shrunk on fins and a separate head. The liner went in the freezer and then later the fins were heated with a hot air gun.
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See part one here  part two  part three  part four  part five  part six  part seven  part eight 

part nine  part 10  part 11  part 12  part 13  part 14