Hi,

The NS125F and R barrel is very different from the NS400/NS250 barrel. The NS125F was honda designed, but made in Italy. The NS400 barrels are only different from the NS250 by being 57mm instead of 56mm.

Although havng said that - the NS400 pistons are also really hard to get hold of. It doesn't help that they are graded ABC to match the plating sizes and you need to match the psiton to the barrel. I think B size NS400 pistons are still available.

Terry Shepherd does a 500cc conversion for the NS400, that uses 64mm pistons, a last resort would be to go down that route with the NS250.

NS400 top ends turn up on ebay every now and again, I have a couple of spare top ends in the garage for my bike. Swapping the NS400 top ends would get you out of trouble if you were really stuck.

Cheers, Mat.