David Hill wrote in message .. .
I'm working on a replica of a 1924 airplane originally powered by an
Indian Chief motorcycle engine. I've spent a year or two trying to find
a modern engine that somewhat resembles the Indian, and the best I have
come up with is a Harley-Davidson.

Looks like with an 80 cid Evolution engine I can get ~40 hp at ~3400 rpm
(direct drive) or ~60 hp at ~4500 rpm (PSRU setup).

Has anyone here tried this? Or know of anyone who has done this? I'm
looking for caveats, tips, and techniques. Based on experience, not
opinion. Oh, sorry, I forgot where I was. grin

Second hand caveat: This topic has been beaten to death, buried,
resurrected and beaten to death several more times on the gyro forum.
As I recall, the problem is heat. Running at the rpm we need to spin a
prop is too much for a motorcycle engine. After initial acceleration,
they basically loaf down the road. The sustained revs will fry them.
This what I recall being posted by people who seemed to know what they
were talking about. Craig Wall had some very spirited and seemingly
logical and convincing posts as to why they won't work. But then
again, someone may prove them wrong and get one to successfully
perform. I don't believe anyone has a good handle on it yet, with
proven reliability over a substantial amount of hours.

Ken J. - SDCAUSA