My sons 300ex engine dropped the cylinder sleeve and pretty much scattered everywhere in the lower end. The bottom of sleeve looked like something took a bite out of it. Jagged broken edges all the way around. Only engine mods were a stage 1 cam and 11.5 compression wiseco piston. Apparently the ring on top of cylinder somehow let loose dropping the sleeve down. (Now the rest of story) Motor was run in Febuary for about 15 min. with no oil. (Please don't ask how) A few minutes of this in 5th gear WOT. Cooled down and started right up next day (with oil) and ran fine for about 3-4 hrs. of riding before finally smoking and increasingly more noisy. Top end was rebuilt with new cam valves, seals, rocker arms, piston and rings in March. Mechanic said rest should be fine. Ran it another 6 months with no problems at all till now and this is when sleeve dropped. He said he has never saw a sleeve drop. He's been rebuilding engines for 15+ yrs. Anyone with engine BUILDING EXPIERENCE please give me your opnion. Could the lack of oil several months ago caused this OR did he do something wrong when he rebuilt top end? OR Just a freak thing? Sorry for long post. BTW the crank, crank bearings and rod are in good shape.

 

seen this when racing B&S 5hp open modified. Leaned engine out to much in staights and heated the block so much sleeve done same thing the next race. You will need a new jug or it wil just do it again one day.