A 5cc VERSION OF THE CLASSIC ED HUNTER

Part one by Ramon Wilson

The ED (Electronic Developments) 3.46 cc 'Hunter' has long been a 'favourite' engine. The thought of a 5cc version didn't take long to manifest itself and a GA was laid out and a preliminary set of drawings done.

The usual start (as described on earlier engines) made to hack out a crankcase from ali block.
The cases were easy enough to machine; only the bosses where the backplate screws to presenting a small challenge.
The crankshafts were made using a combination of EN24t and high tensile cap head material. This saves on En24t and has proved to more than stand up to the forces involved. The fixture is for turning the crank pins.....
.... using the faceplate.
Finished except for the taper for the prop driver. One of those small revolving centres from Arc Euro was needed to do that. 
The cylinders do not have a liner and as such are turned from leaded EN1a. The machining was relatively straightforward but the two bulges that are over the transfer passages required a different approach. First up was to finish turn the bore and rough turn the basic ODs
Make a new expanding mandrel to suit the bore and machine the fins and lower flange dimensions
Then modify an old one to hold it on the mill .....
The teeth of an end mill cutter were modified on the offhand grinder.....
...... to plunge mill the transfer passages in to an exact depth
Set back on the longer mandrel, the exhaust side of the case had the relief milled
Finished examples with the transfer side to do - the bulges required can be seen in the drawing. Assuming the original was machined on a copy lathe, but with no access to one, another method was sought.
 
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