I've just bought one of these off the bay so will probably be needing pistons and rings at some point in the future. How different is the NS125R from the same period ('86-'87) as it has the same bore and the pistons are available in a few different sizes over bored, just the position of the gudgeon pin would be a worry as I've not got the NS250 so have yet to take it apart to look. But you can get rods the aswell as the stroke is the either same or close enough, skimming the castings or thicker/extra gaskets would sort that out, or use other rods with a suitable offset between the eyes.
If Honda saved themselves time by basing the 250 motor on the RS then whats the betting they saved even more by basing the 125 motor on the 250? Can't see if anyone has tried it anywhere on the web and it would save farting about with NS400 pistons.
The spec of the piston in the NS125 (10229) is listed here so does anyone have thier NS250 motor in bits or a piston to compare?
I'm picking up the bike I bought from ebay on saturday and the motor will probably be removed over the following week but the plan was to send it off whole to have some work done to it. So it's a toss up between just packing it off whole and have them sort and try it, or spend £23 on a piston and take a barrel off to have a look myself.
There were some s/h ones on ebay a few days ago - they were listed as NS400 items, being for the smaller capacity South African model. The lister stated they were suitable for an NS250 as well. I am at work and cannot check to see if the auction is still current (damn IT dept!).
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.
And from memory the smaller capacity South African (only) NS400 had smaller diameter pistons, didn't it (56 instead of 57mm)? IF these are the right size - it may open another avenue of enquiry. This was what was specified in the ebay listing, which appears to have ended. The seller still has a heap of bits listed, and you could probably contact him to see if they sold, or he has another set.
I am not in any way connected with the seller - I just happened to notice the items prior to reading this thread. And on the chance that they might be suitable and get someone out of trouble - refer to Andy's post #3.
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I did a few searches and nothing like that came up. Got a link?
