My first NSR lasted 12min on the track. The previous owner had changed the crank and gave me the old one to show.

I don't known if he bought a used or what happened, but the big end bearing had all broken up and slapped the piston against the sides of the cylinder so the skirt broke and somewhere in between the the ring broke and pieces of it, found its way to the top and smashed the top.

BUT, I've never dismantled an NSR and only taken the crank out of an MZ before and that wasn't even airtight afterwards, but with the help of the old NSR e-mail list, a japanese manual, a parts manual and a few conversations with Matt and Paul in Thailand, I did the work.
I had the previous crank checked and the outer bearings changed locally. The cylinder was replated by Apex.

I did all the work myself and 2 years after its still running, and this is an all out trackbike.

Slow meticoulous work, and a few hints like the left hand thread on the RC valves and how to place the rings and which way to install the pistons and you can do it.

No, I don't have a workshop (but no wife either) so the engine was dis- and assempled in the kitchen.
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom