Hi Guy,

The NS250R MC11 pistons were sized A, B, C, A being the largest C being the smallest, although there's hardly any difference between them all, none of the standard pistons are available from Honda now so aftermarket pistons from another model have to be used, ideally you would want to replate the cylinders when fitting new pistons.

Another option would be to fit a used set of cylinders and pistons from the NS400R as they will fit straight on and increase capacity to around 260cc. Another option if you use the 400 cylinders (250 cylinder walls are thinner) is to bore them out, both 300cc (61mm) and 320cc (63mm) are possible with re machined heads to suit.

If you need any more info please PM me.

Cheers Ian