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

The backplates began as 35mm long blocks of 38 mm square HE30 Aluminium. First off was to bring them square and 1mm up on all faces and centre drill for the venturi position and the register on the opposite face.


The intake hole was drilled and the taper turned then the block reversed for turning the register and recess for the rotor plate. The red blocks are 6mm perspex which makes for very good protective packing.


Next up was to press that previously made drill jig into service and drill the bolt holes.


Then set the blocks up on the rotary table for milling the intake cavity. This shows the leading and trailing edges being defined (important) - before removing the waste - (not so important).


Next up was to rough out around the intake tube then set them up in a clamp plate on the face plate for finishing to thickness and turning the taper on the intake tube OD.


With that done the plate was transferred to the rotary table on the mill for roughing and finish milling the pocket in the back.


The bolt bosses were milled - note the pin for indexing rather than setting up each hole.


After a good initial fettling and smoothing with Scotchbrite and Garryflex that clamp plate was pressed into service once more for cross drilling and tapping the 2BA holes for the spray bar


And again for milling the side angles


And yet again for milling the clearance for the bolt head in the intake tube.

This simple little plate has really earned its keep on these backplates and still has work to do on the front housings. An easily made and versatile fixture that possesses some extremely good work-holding characteristics. They are particularly good when used for machining eccentrics, too.


After another fettling they ended up like this.



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


Click on drawing to download - for personal use only.
 

IMPORTANT NOTE FROM RAMON ABOUT THE ROTOR PIN


I had two really super very fast and extremely consistent runs with the Elite Mk2 at the Forncett annual ME Day which was very pleasing. However, when cleaning down on the Monday I had course to strip the Mk 1 down as the rotor pin had come loose. I removed it with intention to add a drop of Loctite then, when cleaning the oil off, it snapped in two at the thread relief. Despite tempering well it obviously was quite brittle. I now intend to strip all engines and replace the pins with new ones made from EN24T without any further heat treatment. ( I would think making them from a high tensile cap head would be a suitable alternative)

 

All heat treated to the same standard this is the only one that has failed but the risk of potential damage to an engine whilst running is to great to take. I think it might be a good idea to bring this to the attention of your readers.