Join Date: Feb 2010
Years Riding: since 1966
How you found us: Honda305.com
Could be right. It's hard to see in the picture, but it does look like the big end is overheated. For here it looks like the piston has seized as well.
I'd spend some time examining parts to be 110% sure of the cause. We don't often see that much top end damage from a simple big end failure. Of course that depends on how long it was run after the damage started. If it continued to run and bits of big end cage were coming up through the transfers, that might have caused the rings to jam and allow the piston to overheat and cause the seizures.
There is certainly a lot of debris in the top end and much of it is small balls which I took to be detonated piston, but it may have come from the cage.
That motor is very similar to the RS250R. Had a 96 to rebuild a couple of years ago. Transfers were much larger IIRC.
RSCycles for parts or is there a better source for street motors?