piston sleve crack
#2
Too hot, too lean and/or bad lubrication.
#3
I think after I change fuel from cosmo to techlube 25% after 3lap then the engine stop and temp around 105 degree on my ninja mr21, I try techlube as my supplier asking to try it out but end up I crack my liner but piston and conrod still in good condition no mark on the piston either the conrod
#4
I know nothing about either fuel but if the motor wasn't 330 degrees f, my first thought would be the fuel and since you just switched fuels, I would tell him to rethink his formula. If it doesn't contain at least 6% castor, things like that can happen. I bet he was trying an all synthetic blend or maybe a 50/50 (4% synth, 4% castor for instance). Might work for offroad or short tracks but not on a fast 1/8th onroad track.