A rider just seized his crank on his big bore MXer. (true story) That never happens without good reason. Here's the 3 reasons I know of:
1) he was using an engine oil at 14% too high a ratio (this I know because I created the worlds best estimator of needed oil based on the products viscosity, the engines max RPM, and the type engine cooling and it told me he screwed up on the ratio by 14%),
2) his bike has a carb with 12% less area than is needed for best peak power (which I know from my carb sizing calculator) which means the air velocity in it is 12% too high which increases the shearing off of fuel droplets so the result is smaller droplets. The big ones are needed to carry oil to the bearings so if they are sheared too much then they change from large droplets to medium sized ones.,
3) He has a carb with a needle jet with a bigger diameter than normal which requires less needle clearance for a normal flow area at WOT and so because this "nozzle" (needle to jet clearance) is smaller than normal this adds to the predisposition of it to not make enough large fuel droplets which are needed to carry oil to the bearings.
Those 2 spreadsheets cost $20 total, a mere pittance compared to the cost of replacing the low end, not to mention all the headache involved. Oh, for those who hate the idea of using spreadsheets, I also offer to do the work for you for a small fee. Just give me the data, that's all. No other 2 stroke software company offers that much service. Good software can improve both power and reliability. www.dragonfly75.com/moto/calculators.html