I have an OS Max .50 FSRH (helicopter engine) and it really runs nice but it has very little compression compared to my other engines. (I use it on a plane as I gave up on Choppers for a few years.) Is this normal? I really never noticed it until a buddy was looking at it and was spinning the prop with his hand. It is ringed could that have something to do with it?

Again, thanks for all your help. Some day it will be me helping someone!

Ringed engines will appear to have poor compression when turned over slowly. If it runs well - it's fine.

Some heli engine have a extra head shim to decompress them a bit. It makes the eng run at a steadier rpm so you don't have to compensate as much when you are hovering.
Pull the head off and remove the shims and you will gain some more performance for your airplane.

One of the fellows I fly with resurrected an old Goldberg Tiger which is powered by a .50 FSR. Same low compression when spun by hand...

And it starts, idles and runs perfectly.

"Don't fix it if it ain't broke."

i have an enya that i believe is ringed and flips over very easily which is because its ringed. Actually i like it better because its easy to turn over!!