Pistons a, b, c, d sizes??

I'm getting a bit confused about pistons. I'm sending my cylinder in to be replated to stock bore. I want to get the top end kit and don't want to wait to send the piston with the cylinder. I'm looking at getting a Pro X piston. They have three different sizes. B, C, and D which are each .01mm difference. The total from the smallest to the biggest is only .02mm or .0007". Thats a ridiculously small difference. Which one should I be getting?

Ask them what they consider stock bore. A B size piston is the closest to that, but double check with the plater. 

Yamaha offers A,B,C, and D pistons. Not sure about other piston manufacturers

I gave up thinking so much about it.. I read somewhere that B was the normal size and the others are for minor differences in manufacturing tolerances. I ordered the B piston and wrote on the work order to match that size if possible. Good enough..

Cylinder should have letter on back not sure what year your talking.  Personally I always get D 

1996. I looked for a letter and couldnt find one. Only thibg I saw was a casting mark that said "95" and "U". Its bought now and the cylinder is on the way to the plater. I'm done thinking for a bit.. Lol

3 minutes ago, Motox367 said:

Cylinder should have letter on back not sure what year your talking.  Personally I always get D 

Like this one but hard to see as yours might be

0130181815.jpg

Oh 96 ok well they will match whatever one you send or by a weisco and send that👍👍

Like this one but hard to see as yours might be
0130181815.thumb.jpg.f0b31ad53077942078883ba1527ad353.jpg

There was definitely nothing there.

Keep in mind the factory service manual specs are for a cast piston in mind.

If using a forged piston, use that manufacturer's specs, not Yamaha.  

 

Avoid surprises, discuss this with the re-plater.

 

 

 

 

It's a cast Pros piston. I noted to the plater what I'm using.

6 hours ago, warlok1469 said:

 

I'm getting a bit confused about pistons. I'm sending my cylinder in to be replated to stock bore. I want to get the top end kit and don't want to wait to send the piston with the cylinder. I'm looking at getting a Pro X piston. They have three different sizes. B, C, and D which are each .01mm difference. The total from the smallest to the biggest is only .02mm or .0007". Thats a ridiculously small difference. Which one should I be getting?

 

Vertex comes in ABCD, and it is best to go with A for a replate. 

The Vertex "a" is 67.94mm and the ProX "b" I have one the way is 67.95mm. Less than .0004" difference.. Close enough for me.. And already paid for.

Factory yamaha used A cylinders with D pistons and a properly gapped piston ring. 

Factory Yamaha race teams also had infinite supplies of pistons, rings, cylinders etc. if experiments went wrong.

They also had expert engine tuners and mechanics which tore down and rebuilt the engine after each race.

An extra 1 horsepower was well worth any risk of damage as long as the engine lasted until the last lap.

 

With a 1996 bike, spare parts are not doubt getting scarce and,

the OP likely doesn't want to tear into the engine sooner than expected.

Yep I've installed a C piston in an A cylinder before but apart from uneven wear, nothing was gained.

Following factory service manual specs if the safest bet.

 

Edited by mlatour

Simply stating that you can make any of the 4 work. Most important is to make sure you have a properly gapped ring. It will allow you to run any of the 4 sizes. 

You all make very valid points. Thanks for all the input.

IMO if you're getting it replated, tell them to make it stock size and get the closest to stock (as has been mentioned).

I've never understood getting a cylinder plated to match the piston. The piston is a wear item. Then you run into this same problem every time you do a top end piston swap. Make it stock bore when you replate, and then you can use whatever piston manufacturer you want, several times between each replate.

Jmo.

3 minutes ago, Bron-Yr-Aur said:

IMO if you're getting it replated, tell them to make it stock size and get the closest to stock (as has been mentioned).

I've never understood getting a cylinder plated to match the piston. The piston is a wear item. Then you run into this same problem every time you do a top end piston swap. Make it stock bore when you replate, and then you can use whatever piston manufacturer you want, several times between each replate.

Jmo.

It ensures a consistent and perfect fit. That way when you start with the A piston, it’s perfect for the new cylinder. As it wears and goes out of tolerance, you put in a B piston to compensate for the wear. If all goes smoothly with no other problems, you should be able to keep swapping pistons until you get to D, at which point the cylinder would be out of spec and you get it replated again.

It ensures a consistent and perfect fit. That way when you start with the A piston, it’s perfect for the new cylinder. As it wears and goes out of tolerance, you put in a B piston to compensate for the wear. If all goes smoothly with no other problems, you should be able to keep swapping pistons until you get to D, at which point the cylinder would be out of spec and you get it replated again.

But pistons aren't always manufactured in spec. They're not perfect. However, a millimeter is a millimeter, no variance. Make the bore stock spec, and then there's no possibility of problems down the road.

 

Yes, the concept is great, but things don't always go well with pistons. Besides, as has already been mentioned, the difference between letters is negligible. I don't see posts like the OP's from members who are buying a piston for a stock bore.

 

I always either send the piston with the cylinder and have them match it or just buy the piston through the plater themselves.

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