My cylinders are stamped "B". They also have the letters "xp" painted on the left corner from where the "B" is stamped. Is that "xp" an original marking or has this engine been messed with.

Looking in the parts book they list, "B", "C" & "D" pistons. What are the differences between these pistons. I know I need to get a "B" piston but I want to know what the differences are for my own knowledge.

Thanks.

B cylinder needs 'no mark' piston.

I know you help a lot around here Matt so only if you feel like explaining why and what the differences are, I'd sure like to know.

I just looked in the book and sure enough I was jumping to conclusions. It lists "B", " ", "D".

So I would need the middle one. Why wouldn't I need the B?

Thanks.

Because that's the way Honda designate NSR250 pistons!

The NSR150 goes A/A, B/B, C/C, but the 250 doesn't. It would certainly be easier if it was the same as the 150, but it's not.

Honda only gave piston size information with the part numbers for the MC18. have a look at the MC18 section of the parts manual for an idea.
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MC28:

Cyl A - 54.008~54.011
Cyl B - 54.004~54.008
Cyl C - 54.000~54.004

Pis B - 53.966~53.969
Pis "" - 53.962~53.965
Pis D - 53.958~53.961

So there you have it. Strange lettering system, but that's Honda for ya.

When I raced the 28 we had B cylinders and used B & D pistons depending on the circuit. B (tight) pistons for short, point and squirt circuits and D (loose) pistons for circuits with long straights. The idea being that the tight pistons would give good comp, so good drive out the turns, whereas the loose pistons were good for flat in sixth for ever straights. The pistons could get warm without fear of nipping up, which may have happened if we ran the B pistons on the flat out stuff.

Never had a failure.


Last edited by Matt@TYGA on Mon Sep 10, 2007 1:28 am; edited 1 time in total

Great technical info, this is what I needed.

Thanks.