When is it time to replace the rings on a Glow engine?

I have an OS 50sx-h (not hyper). I bought it many years ago and ran it a lot. Sorry I have no actual running hour data. I just replaced the bearings and now it seems to lack compresion, but that is just an unscientific evaluation made by flipping the prop. I am thinking about buying a compression gage and testing all my engines. I have just bought a used OS 1.40rx in a pattern plane. Pattertn planes get run a lot and maybe I need to pay closer attention to rebuilding.

If the engine hasn't run since the bearings were installed, run the engine first. Ringed engines get soft sometimes after the piston is pulled out and reinstalled. The ring has to re-seat against the cylinder.

If its still soft after running, put a Frank Bowman ring in it, break it in, and go fly. I suggest to anyone rebuilding a ringed engine to replace the ring if you're replacing the bearings. It just makes sense since the ring is only $12 extra.

Oh, and IMHO, forget about a compression tester. I think it's pointless on these small engines.

Yes I concur, after disassembling a engine you can never get the cylinder and piston aligned exactly like it was before. But the ring should reseat itself again OK after a while. I usually replace the ring as well as the bearings on a engine that has some time on it. So you just need to run the engine some more and it should start running OK again. But if it doesn't then put in a Frank Bowman ring, they are better than the OEM rings in most cases.

I've only fitted new rings to an engine once (Enya 45 model 6001 with twin rings) after a couple of hundred hours of running because it was beginning to need several flicks to hand start although once running it was still as good as ever. This was for competitive CL stunt where one flick starts were a badge of honour . However, over the years I used to strip the engine to give it a good clean out and then it needed several tanks of fuel to reseat the rings and regain its normal hand start compression feel (and one flick starts). For the other 99% who use an electric starter I'm not sure how you could judge ring wear other than maybe a loss of power. The problem there is that, like all things that happen slowly, you may not be aware of a gradual drop in power. I might add that this Enya still has its original bearings. Thank you Castrol M .

I don't think it's fair to compare an Enya to an OS. It's been well documented that the modern OS engines are not made with real great bearings to start with. Much less, Enya is legendary for its longevity anyway.

So I'll ammend my thoughts to re-ringing during a bearing swap/rebuild on almost all other engines except Enya.