Piston size question

[ridehonda400ex]

I picked up a 2000 rm125 that needs a top and bottom end rebuild. i have all the parts besides the piston and rings. the piston in it now says 53.98 could i get by running a 53.95 piston?

[dxcody]

I dont think so, but idk

BUMP!

[300ex_#387]

If you already have it try putting it in the cylinder and check your ring gap and see what it is. I would think you could run it but I am not positive.

[ridehonda400ex]

Well i dont have the piston yet. I just cannot manage to find the size thats in it now. I found a 54mm from wiseco on rmatv but i worry it might be to big

[dxcody]

i found dozens on ebay when i was trying to figure out if it would work, they say kx125 but that shouldnt matter right?

Heres the link if you wanna check it out.
http://www.ebay.com/itm/PRO-X-53-98-MM-PISTON-KIT-KAWASAKI-KX-125-1998-2000-/230721518002?pt=Motorcycles_Parts_Accessories&vxp=mtr&hash=item35b812f9b2

After all suzuki and kawi suposably make their bikes the same anyways

[300ex_#387]

Originally posted by ridehonda400ex
Well i dont have the piston yet. I just cannot manage to find the size thats in it now. I found a 54mm from wiseco on rmatv but i worry it might be to big

The standard bore for that bike is 54mm. Is it the stock jug? I would think you would need the 54mm piston. Usually the pistons are slightly smaller than the actual bore. I'm assuming they list it as a 54mm piston to show it will fit a 54mm bore. If you actually measure it it may be a tad smaller than 54mm. Can you measure the bore of your cylinder?

[250x_kyle]

Originally posted by 300ex_#387
The standard bore for that bike is 54mm. Is it the stock jug? I would think you would need the 54mm piston. Usually the pistons are slightly smaller than the actual bore. I'm assuming they list it as a 54mm piston to show it will fit a 54mm bore. If you actually measure it it may be a tad smaller than 54mm. Can you measure the bore of your cylinder?

the only way to measure the cylinder accurately in that small of an incremental distance would be with a bore gage. it may run but it is one and one tenth of a thou undersized. wich in the end would only make it five tenths of a thou undersized all together. it would probably all come down to fitment.

[MichaelS693]

If the size of it now is 54mm and it needs to be rebuilt then you would bore it around .5mm over(which would be around 54.5?-54.6?) or so(that's the next size up I believe) which would bring the piston that you need to a 54.5mm(give or take a thousandth depending). Then it would have to be honed to match it exactly and to smooth the walls out. Unless no bore is needed then get the stock piston size that it says on the specs...Right? Makes sense to me. Or I could be completely wrong

[300ex_#387]

Actually people dont really bore these cylinders. You can get them resleeved to a bigger bore but when it gets wore out most people have them replated. Im guessing you just need a 54mm piston kit. I think you would be safe with that as long as it is the stock cylinder and sleeve.

The best way to check fitment is to try a piston and check the ring gap. That will tell you if it will work or not.