Have just completed and run this engine. Casting and drawings from Hemingway Kits. It started easily ,once I had the settings correct and has had four runs of three minutes each, so far at 5600 RPM with an 8×6 inch nylon prop. I have differed from original design with the cooling fins and made a collet type prop driver. The original had a steel driver locating on an 0.020"step in the crankshaft. Crankcase has been bead blasted plus red anodising for the other external aluminium parts . Working this small has been quite interesting.
I see that Hemingway Kits have "L W Sparey"; L H is, of course, the author of the excellent "The Amateur's Lathe". Were there two and, if so, were they related?
Nice looking work, the anodising certainly brightens the engine up.
Is the piston the wrong way around in the picture, if not there's a lot above the pin.
Did you leave the back of the crankcase out, I see a retaining ring.