This one was sent in by Steve Betney from England. It's a small elderly spark ignition engine of clearly British origin, based on the threads used in its construction. Displacement is around 2 cc.

This very interesting engine came from the historic Keith Harris collection. It was unidentified, and has so far confounded all experts who have seen it. Richard Dalby reportedly hazarded a guess that it might have been made by G. W. W. Harris around 1945/6, but he didn't have any real conviction about this or hard evidence to back it up. Mike Beach, Mike Clanford and Eric Offen didn't have a clue either.

Very unusually, the spark plug has a 5/16" x 24tpi (AF) installation thread. Not surprisingly, the engine arrived without a plug! The one fitted now was obtained separately and is the only such plug that Steve has ever seen. It looks to be home-made. 

The crankshaft thread is 4BA, perhaps a bit under-engineered. The cylinder head & hold-down threads are 8BA & 6BA respectively. Needle is 8BA. The split crankcase screws are 3/32" x 48tpi (BSW). The castings are extremely precise & accurate, to the point that it's hard to see the vertical crankcase split join line. Overall, the engine is very well made indeed, with excellent internal fits & good compression. 

There is no drive coupling from the substantial flywheel which is mounted on the rather insubstantial shaft, but the engine was obviously made with  boat or car use in mind. There are no mounting witness marks on  the lugs, creating the impression that the engine may not have done any real running in its long life. Steve would love to install it in an appropriate period tethered car of smallish proportions, but first he needs to know who made it and when!

I'd hazard a guess that this is the product of one of the many talented individuals who became involved with either tethered hydroplanes or tether cars during the early post-WW2 period. Can anyone out there be more specific?!? If so, please get in touch through the email link provided!