Worn out Two Stroke main bearing areas.
Anyone who has rebuilt a few two stroke engine has seen case were the main bearing has been spinning in the case do to bearing failure. I have seen people throw out blocks or bottom covers from this. Here is a little trick I use to fix some of them. Masking Tape. Yep just tape. You could use real thin brass strips but just plain old masking tape works pretty good for me. Here is a picture.
I just clean the oil off the main bearing and stick the tape to it on covers or bearings that show evidence is “spinning” of the outer race. If it is real bad I put it on the block 1/2 too but most the time only the case cover are is worn (that’s were all the force of the pistons coming down under power pushes in). Pretty simple I know. But been doing it for years and anytime I take an engine. Down that I did this too…there is the tape. Any extra thickness seems to get squirted out and passed by the engine. Since it is only tape it does no damage anywhere. Try it sometime.