96 RM250 cylinder overbore?

I just bought a 96 RM which is very clean and came with a reciept for recent engine work totalling more that the sale price.

The guy I bought it from wasnt very mechanically minded and gave me a bit of a cryptic description basically saying it had been rebuilt with the old piston as it was in good shape and the shop had the ordered in wrong one as it needed an oversize and they had a standard. He went on to say that the new piston and the price of fitting was already paid for so it could go back in for the work free of charge once the piston came in.

I contacted the shop to get clarification and was told that they thought either the barrel had been changed for a 95 or older (it hasnt i checked the parts fiche and the power valve cover is different) or it had been bored out to accept a 67mm piston and they had a stock piston which was 66.4mm.

I have asked them just to give me the piston and gasket set as I am quite happy to fit it myself and the bike has great compression so i wouldnt be rushing in to fitting it as it really doesnt need it yet.

Has anyone heard of this been done before, boring out a 96 onward cylinder to accept a pre 96 piston? is this a good idea will it cause any problems?

Can it be undone ie replated up to the right size? Or would i need to fit a liner and would this be ok as ive heard mixed reports about fitting liners



Well I found out it cant be replated to size so its either to be lined, the barrel replaced or left as is.

I have found a 98 barrel for a decent price would this be a straight swap? Any opinions on the best course of action would be appreciated.


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