Hi,

I bought an NSR250 mc16 recently. The engine was seized when I bought it, but I picked up the bike for next so nothing so it was still a good deal. I've since stripped the whole engine down and found the crank bearing to be rusted. I'm planning a full engine and bike rebuild, but I've run into one or two confusing issues.

I managed to find a replacement mc16 crank, but when it tried it in my cases it wouldn't fit. A side by side comparison with the old crank showed it was considerably different. I now believe that this bike was fitted with an mc18 engine, but It could be a 21 bottom end. I've been searching this site high and low trying to figure out what engine I have. There's lots of information, but nothing that says these engine numbers = this model, or something like that.

The engine number is MC16E-1130166, the barrels and heads look to be mc18's (hexagonal with large exhaust ports).
Here's a photo of the exhaust port if someone would like to confirm this.
http://i1253.photobucket.com/albums/hh587/wil_nz/DSCN1176.jpg

Here is a photo of the crank if it helps with the identification (old crank on bottom, mc16 crank top).
http://i1253.photobucket.com/albums/hh587/wil_nz/DSCN1175.jpg

I would really appreciate it if one of you knowledgeable nsr folks could help me id this engine. As so many nsr engine parts seem to not be interchangeable, I'd like to know exactly which parts I need to find to rebuild this engine.