After installation and the cases cool, can you feel some play on the inner race? Are you using C4 fit? When you put the bearing in do you weight it down with a big aluminum block to keep the bearing cool and seated? The hot case can push the bearing up. There is supposed to be a hole that connects the transfer passage with the space between the bearing and the crank seal, is it open? This draws lube through the bearing from differential of pressures. After you run it on track does it still have end play in the crank? The bearings could be drifting out of the pockets. Do you have a bent axle or sprocket that could be jerking the engine shaft, does your chain pulsate are your tires balanced, frame cracked? Pull the spark plug and crank the motor over fast and listen for any metallic clank, piston hitting something. Does the piston twist going up and down? Sorry for the unicorns I ran out of zebras.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience