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markvan

00 426 - Different cylinder sizes???

8 posts in this topic

I'm putting in a fresh top end in my 00 426. This is the first rebuild it has had. I went to order the new rings from my local shop, and am told that there are A, B, C, and D, sized cylinders. He is saying that there should be a factory stamp somewhere on the cylinder saying what size I need. The cylinder has never been bored, and has relatively low hours. (considering it's a 2000), so the original sized rings should be ok. (right?) Anyway, anyone know about this? Where do i find this stamp? I don't see it anywhere...

thanks guys...

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Not saying this absolutely isn't true, but I will say after multiple years of reading here I've never read anything to make me think this is the case.

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I have 2 (2001) 426 cylinders sitting on my bench that I just looked at and there are no A,B,C,or D stamps anywhere, there is a stamp with some numbers that is in black ink on both of them (both different) and on only one of the cylinders there is an "F" stamped on it all by itself.

Those are the only markings I can see.

When you look on the Yamaha parts fische online there is only one part number listed for the rings and the same for the piston, however they have a (std) listed next to the part number.

If you are not going to bore it and are just putting in a piston and rings, then I would order the (std) parts listed in the parts fische.

The part numbrs are:

5JG-11631-00-00 PISTON (STD)

5JG-11603-00-00 PISTON RING SET (STD)

5JG-11633-00-00 PIN, PISTON

93420-19084-00 CIRCLIP (you need 2 of these)

Make sure you use a bore guage on the small end of the rod to check for roundness, the small ends go bad and you dont want to rebuild it with a bad rod.

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Some bikes have the cylinders sized.....A, B, etc. KTMs if I remember correctly.

If the parts microfiche only shows one piston part number, then don't worry about it.

Have a shop mike it to make sure it's in spec., then mike the piston and you will be sure.

You can find the nominal sizes for cylinders and pistons in the shop manual.

It also tells you where to take the measurements.

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Usually the A,B,C,D pistons are usually marked on 2 stroke cylinders. I have never seen them for 4 stroke cylinders. Maybe KTM but I have never worked on those bikes before. Just use the part numbers that TeamScream gave and you should be fine. On 2 stroke cylinders like Honda or even Yamaha , they will be marked on the intake side of the cylinder. Honda punch marks their cylinders and Yamaha usually uses ink markings.

Plus, those cylinders can't be bored because they are a Nicosil cylinder. Just give it a good hone and you will be good to go.

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Hey man don't listen to that idiot from your local shop, the person that helped you obviously doesn't know the modern yamaha engine. Yamaha only offers std size componets. So YZ400, 426, 450 have specific bore sizes and that is it. They are either in tolerence or they are not. Tell them to open up the owner/service manual and get familiar with the products they are selling. Just make sure you get your cylinder mic'd and make sure it is in spec.

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I beg to differ with you. Back when i re-did my '00 426 it had a letter on it somewhere (I've got CRS...can't remember squat) and I based my re-ordered piston on that letter. FYI, there wasn't a huge diff in sizing, but there was a diff.

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