I just got done with a complete engine rebuild on my son's RM65.
It all started with a piston seizure. I replaced the piston had the cylinder cleaned up and replaced the top bearing. The rod had NO up and down movement, but seemed a little shaky on the side to side. Remembering what I'd heard about side to side being okay, I fired her up and let the little man have at it (after break in). Within an hour, maybe two, it seized again. This time the big end bearing flew apart and DESTROYED the entire power portion of the engine. Had I taken a really hard look at the big end, I'd have saved myself a piston, cylinder, and head, etc. :bang:
It's pretty difficult to get a good look at the big end and harder still to rationalize splitting the case unless it's absolutely necessary, but after a seizure you need to take a long hard look at things because of the stress and heat that accompany a seizure event. Make SURE the copper washers are intact and that lateral movement is within spec. Look for for signs of discoloration from overheating. Any little tic as you roll the rod around the crank. And don't be afraid to do the work BEFORE it's too late. It'll save you money and heart ache in the long run. :cool: