I just finished cutting some 300 cylinders and it's now peeing down with rain outside so i can't be bothered to go home.

Decided to have a trawl through some old posts and this one sprung up.

As Andy says the F3 special part is required to fit the F3 piston because of it's 14mm piston pin, but it's obviously not common knowledge that the RS125 NX4 and RS250 NX5 have a 15mm pin so will basically pop straight on.

The piston heights are different to std NSR so machining of cylinders is necessary, but that's quite an easy task.

Both NX4 and NX5 actually use the same piston pin as the NSR. Yes it's a KV3 part.

I have a set of NX4 kit pistons that I've never got around to using, but maybe one day when I've got nothing to do I'll fit them into something.

Not exactly a breakthough but someone might find this info useful.