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 .