About 10 years ago I bought a .61SF ABC from a friend that thought he needed to replace it. He has since worn out TWO .61FX's, while the SF he sold me (cheap) still runs great and still seems to make all the power it ever did. With the plug removed, there is no discernable "pinch" around TDC, but the engine doesn't seem to care. I don't fly it as often as I used to, as now I burn mostly gas and kerosene. I'll never part with it, though. It's just been too good an engine to get rid of.