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i really need your help

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i need to order a new top end for my 2000 rm80. the previous owner said he replaced it before and bored it over a little and doesnt know how much or what size the piston is. but i cant seem tofind the size of the piston. it has these things on it

7901e

645m04800

and on the bottom of it 604

how do i find out the size of it?

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there is some really confusing way of doing it using some liquid. it would probably require you to take apart the whole / most of the engine or maybe just the cylinder head (not sure) and pour water in there till it's filled, then measure that amount. something along those lines. PLEASE dont try this without reading about it first though i'm sure you could find a thread on here somewhere.

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if it's a wiseco (which them weird numbers look familar to the ones on my last wiseco) it will have ( .50, .75 ect..) stamped on the top. since it doesn't and just has manufacturing numbers then it should be stock bore. all i have ever seen have the overbore stamped on the top of the piston, and if not it is stock bore.and i've done 5 top ends on 5 different bikes in the last 3 months... i could be wrong but from all i have done thats how it went.

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Just use a calipers and measure the bore diameter, then subtract the stock bore size, then convert to inches from mm and you will have the overbore size of the piston to order.

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645m04800 is your part number if you look the last four digits are your more 4800 = 48.00mm

stock bore is 47.50mm PN is 645M04750

It seems every single wiseco application is like this!

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you need to check the clearance with a telescopic bore guage and a 1-2inch micrometer. and compare the measurements typically a wiseco calls for .0020" clearance it says right on the box

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If the piston's slapping around in there definately measure like Garage_guy_chris sez. You don't want your piston to look like his. :p

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