Any OS engine that peels a liner was manufactured many years ago. I may be wrong, but as I recall, they changed their manufacturing process in the late 1990s to use copper plating before the nickel. This has never peeled to my knowledge.

I am running 6 OS engines in twins, 4 .46AXs and 2 .25FXs. I couldn't ask for more reliable or easy to set up engines. I do have 2 Evo .46s in a Dual Ace. To date they have run pretty well with only a couple of in flight failures. Bear in mind that a multi engine plane really puts the stress on an engine, especially in the vibration area. I yanked Magnums and GMSs out of planes because I couldn't get the 2 engines to run reliably together. It also seemed that 1 Magnum and 1 GMS would run better than the other. Not very good quality control, in my opinion.

I hope the Evos turn out well because OS does need some competition. I could only keep 2 Magnum .52s running 2 flights out of 3. I am using the individually now. The GMS .47s were better, but one didn't run as well as the other. The AXs normally start in 1 back flip, tune easily and always run. I have 4 GMS .32s and 2 have been replaced under warranty.

All you need to do to find out whether an engine is good is to fly multi-engine. You'll learn soon enough unless you like tuning and setting a lot and don't mind single engine landings.