After much research on this website today regarding rebuilding MC18 cranks, I understand there are sources for rebuilding these cranks with new bearings, seals and thrust washers, but without new connecting rods and crank pins. Seems a little risky.

And with no way of knowing if crank pins have brinneling or rust until it is taken apart, more risk with shipping and assessment cost.

I understand a new MC21 crank will fit in a MC18 with machining of webs, which seems to me to be the best solution. All new all the way around. Are there any other differences between MC21 and MC18 cranks that I have missed?

Is there anyone that has experience doing this milling? In the USA? Does the crank need to be taken apart to do the milling?
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MC21R9N track
MC18R2J track
CBR954
CR250