I have a couple O&R engines I got from a former co-worker, they were his Dad's. They have no size markings on them and his dad has passed away so the only clue I have is when I took the front engine cover off it was stamped inside OR 23 29 UP. The old prop was a TF 7" wood prop. The one I'm working on has excellent compression what fuel and glow plug wood be best ?? I have a Thunderbolt in it and how does the head come off ?? What prop should I use I have a 9-4 on it.
As noted, the head *does not* come off, at least not intentionally. These engines are low-RPM "chuggers", 4" of pitch is far beyond them. 6-7", maybe a 9-6. Performance is low.
The others have warned you, but blowing the entire cylinder off of them at high RPM is a distinct possibility. I did it with a 23 Sideport. You can JB-Weld it back, but that's not going to make it any stronger.
For fear of incurring further wrath, I wouldn't expect either engine to be much good for any stunt plane, or more than lazy sport flying, they are very weak for their dimensions, even compared to other engines of the era. They are *light* for their displacement, but still vibrate a lot, so you have to build the airplane pretty stoutly - by which, the 23 might have the power of a weak Max III 15, but still has to be built to take the vibration of a 29. A Fox 29 (the one built into a Fox 35 case) will blow either one out of the water, in terms of power, same with a McCoy 29 Redhead.
Brett