I have several FSR, SF, FX, AX engines and have flown them all through the years, but not enough to wear any piston/liner out especially only using them for sport plane flying, not racing or pylon type planes. I usually buy used, so I rarely know the true number of seasons on them when I start flying them. The only failure on the SF series was with a .61 and I bought it that way. I've seen a .46 SF once posted on RCU years back with a wiped out liner as well but nothing stated about how it got that way, could have been abuse. I personally never lost one. I had an OS RF 61 for a few years on an Ultra Sport 60 and it did very well. What is cool to note is FSR and SF series engines is that they came in both ABN and ringed versions.