All the posts about seizure has got me thinking. As I intend to keep my NSR for years and ride it lots, I am going to start building up sufficient spares for a full engine rebuild.

For my MC21 model - R8N, the parts list shows 3 barrel sizes, A, B & C. I have read the technical section (thanks Fontyyy!) but can't find an explanation as to why three sizes exist for the one model engine.

Could anybody explain the reason, and what are the actual differences between the 3 types?

Also, does this mean there are 3 types of piston sizes? Jap4 & tyga just list a single 'top end rebuild kit', with no mention of specific barrel types. The parts manual lists Piston, Piston B, Piston D
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

It's a tiny weeny difference, it could just be for manufacturing variance. After all they are stamped up afterwards, it's not in the casting.
Cyliners are marked up A, B or C
Pistons are B, D and no mark.

I can't remember or find a link to what matches what. Somone will know and it'll be here anyway and it's better to measure the clearance anyway.

Jap4 just list what Tyga list.
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Open the head/barrel page of the Online Parts Manual, and the click "notes". The barrel/piston configuration is laid out there.

The differences, as far as I am aware, are manufacturing tolerances. The barrels are/were not all made in the same factory, and also made over many production runs.
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Andy.
NSR-WORLD.COM

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Thanks Guys, I think I've got it now.

Tyga's Honda OEM Top End Kits include a Piston - No Mark. This corresponds to Barrel type B.

If this barrel & piston matching is to do with machining tolerances, its very important to match these up correctly, could it not lead to premature seizure?

In general engineering applications, being out of a tolerance band can lead to galling / pick-up of precision machined component surfaces when mating them together.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Ideally you want to measure them, the a,b,c thing just makes sure they're somewhere in tollerence. Don't mix them wrongly unless you're doing it on purpose to achive a specific clearance.

The part numbers for all the pistons are in the parts manual.
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hi rich. i did my rebuild today and mine had `B` cylinders on so the kits at jap4 are the right ones for mine and when i asked gavin he said that these are the most popular so i was well happy,
also he said he has sold these kits to people with different barrels and they have had no trouble!!!

What?
At least my corner cutting saves money, Honda list all three pistons, for crying out loud, buy the right one!
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I had PM'd Banshee. He got the Piston 'no mark' kit from Jap4 / Tyga, which is the match for his B size barrels.

But for others with A & C barrels, I would take care when ordering a 'Top End Kit', Tyga's website only lists the kit with Piston 'No Mark' and for barrel sizes A & C you will need Piston sizes B & D, according to the OEM manual.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

well said rich!!!!!!

all im saying is they have fitted the pistons with no mark to `A` and `C` cylinders and had no trouble!!!
i know its best to mach the piston to the cylinder but if your stuck its always an option!!!

Well, I've fitted pistons that you can't see the mark on to any old barrel c/w the old clip and base gasket, but even I wouldn't advocate such actions if you've got other options.

I'm sure Matt or Andy will have the sizes lying around somewhere and I'll bet a bottle of Sangsom a "no mark" piston is the smallest.

"We can go when the bottle is empty.....no.....this bottle!"
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Last edited by fontyyy on Tue Mar 25, 2008 3:19 pm; edited 1 time in total

I've got the specs, but not on hand... but you may possibly owe me a bottle of Sangsom!

The pistons will work in any barrel, but there are limits. Small piston/bigger barrel for flat out long straights, big piston in smaller barrel for tight twisties without a long straight! In layman's terms, of course.

You wouldn't be wanting to fit a tight piston and then rag it down the A38, that's for sure.
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Andy.
NSR-WORLD.COM

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Andy wrote:but you may possibly owe me a bottle of Sangsom!

Oh, woe is me, I'll have to buy you one then.
Of course that will entail frequenting a venue that sells it.......

Insurance on the Trans-slap just paid out as well

No, stop! Must use money to pay off overdraft.
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Can I ask something guys....?

Can I use cylinders from the MC21 model to the MC28 model...? Are there any porting differences between them...? Am I going to have any problems if I use the MC21 cylinders with the HRC Card...? Or with the standard Card...?

Thanks
Michael

I have read on this forum that the exhaust porting is different between MC21 & MC28 barrels, whereby the MC28 barrel is in a lower state of tune. Guys - Need some input from others on this point.....

Obviously you need to compare like to like, 21R to 28R, 21SP to 28SP.
Another question out to the forum....any difference between SE & SP barrels??

Then there are the 3 cylinder / piston pair matches, with cylinder sizes A, B + C corresponding to a specific piston size.

Honda UK online parts are saying the MC21SP B cylinder P/N has been superseded to / replaced by the MC28SP A cylinder, with no mention of availability of the MC28SP B cylinder.

I am currently trying to track down a brand new MC21SP B Cylinder (for spares). If the MC28SP B Cylinder has the same porting, OK, but I'm not happy about simply switiching to an A size cylinder, just when I've bought 2 X Top End Piston kits for a B Cylinder.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

SE and SP bikes have the same cylinders.

'21 to '28 porting is different but not enough to really matter, as Honda say, the '21 barrel is deleted and the '28 one is the replacement for it.

Honda supply of new barrels is depleating and they will almOst certainly not be making any more so if you're insisting on new you're going to have to take what you can get, if there are no 'B' cylinders left then that's that unless someone has some in stock somewhere.

Bearing in mind you're on about a near £400 purchase just on the off chance you need it (a new SP barrel) you may as well just get the matching (£40) piston surely?
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