Hi bought my mc28sp in HRC colours this summer.
It was running when I bought it. The guy I bought it from was a trader and traded it for a CB750 and just wanted to sell it.
It was a bargain so I bought it at sight and didn't had time to take it for a drive.

He brought it the next day with his van and the bike didn't want to start.
So i decided to do a strip down and do a top end rebuilt to be sure.
I also cleaned the carbs.

This is how the piston, barrel and head look!
Does someone have any idea what happened here?

1. I see horizontal damage on the pistons.
2. I hardly see any carbon deposit on the head (it looks like it just had been cleaned)
3. the barrel looks far newer on the outside if you compare it with the head and other barrel.
4. The other piston and barrel are fine.

Something major has found its way inside the cylinder.
Looks like you will need a new head and re-lining of the cylinder.
Most likely whatever was in there had made its way out the exhaust.
I would be checking all the intake and in the crank case to see if there is any signs of failure.
Good luck

That looks interesting..

The damage on the head could possibly be a small needle roller. There are a couple of identical marks and they are all fairly uniform. The damage doesn't appear to be as random as you would get with a ring failure.

Horizontal marks on the piston? I'm lost there, unless someone has tried to clean up the piston after it developed a fault. Does the piston have damage which corresponds to the damage on the head?
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If it ain't broke, fix it until it is.

Thanks for the replies.
The needle roller was fine.
The top of the piston too.
S I think the damage was done before and put back together.
The strange thing is that everything looks clean.

Maybe they cleaned it, put it back together and sold the bike.
Bit it was running when I bought it and sounded ok.