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Yesterday Robert Axelrod posted the above photos showing off the NOS(?) early JAP engine he found; and there must be zillions of similar issues: "This motor turned up at Hershey, PA swap meet! Trying to date it! The cam cover is from a later motor, modified to fit this motor! The pinion shaft is extra long and would stick out through the cam cover, so this motor was never a motorcycle engine! Maybe cycle car, aero? Bore and stroke 85.5mmx95mm, rocker arms are numbered 13,14,15,16. I am thinking this motor is a 1906, as the motor # is 6101, case # 1, some of the internal parts-rods, cam followers are stamped #1, any ideas on the year and appaication for this engine will be appreciated! Thank you for your time!"
Within a few hours he received this answer from G. Chivrall: "I acquired an engine like this in about 1978. Only 5 fins and no knuckles on the ends of the pushrod, 85x85mm cylinders, conical valves screw in valve guides mine has fins on the exhaust. Your's looks dead right and the timing cover looks original to me too. I've concluded mine is about 1908. There are engines from "the same drawing board" (V-8s) in the UK Science Museum in an aeroplane and in the Shuttleworth Collection from an airship. There is also a V8 campaigned in VSCC events by Richard Scaldwell (hope thats spelled correctly). These engines are super and well worth getting running. Powerful and economical but very clattery. They get hot, I put a bit of metanol in the petrol. Watch out for cracks between the valve seats,in the flywheels and cranckcase but your's looks in very good order.
The long front mainshaft is a bit of a mystery. I don't think the breather should be connected to the bottom of the crankase. JAP oiling is mysterious but it works. I used a drip feed to the crankcase outboard of the left cylinder (in picture) through a little non return plate valve. Use plenty of "R". It could be from a cyclecar, motorbike or primitive aeroplane. Although the valve gear is different you will probably find that pistons,flywheels and conrods from later engines can be used, and people are making new stuff these days. There is even a chap in Australia who makes 90 Bore castings which are similar to this engine. Google "JAP 90 Bore" and screen out all the oriental motorbile stuff. I believe the 85 bore OHVs pre-date the 90 Bore which is well represented in the literature.There is very little about the 85 bore ohv's. Good luck with it!"
So if you have an unsolved issue. Just give it a try! You never know what may come out.