The OS.91 turns more than 24K in a Dynamax fan and I have never lost a con rod. Make sure you use a fuel with 23% oil, a synthetic/castor blend and use only 5% nitro. The Wildcat 5% Jet-A is a good choice. Or you can add the castor like Jackjet mentions. The only damage I have ever had to an OS.91, besides crash damage, was caused by running too lean. The motor I'm running now has several hundred flights on it, and the only parts that I have replaced are the piston and liner.