Ive never had this trouble yet on an nsr but i can think of 5 nsr barrels and pistons that have gone because of a spun ring, its not that uncommon.

Still all you have to do is get the cylinder replated, new piston and find all the bits.... (findin all the bits is the best part). Was your motor due for its weekly full strip down yet Fontyyy?

You never know though, maybe a grey plug could beee... er... thinking... er.. no cant think of anything else.

I'll call you tomorrow or something fontyyy. Once you have recovered from the drink.
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If I have to take the carbs off once more...