Piston problem,Need help please

[By panosyz400f, Posted December 12, 2004]

I bought my YZ400f 3 months ago and i'm replacing the piston rings on a STD piston.

I do not know if the piston that is on the bike at the moment is the OEM or an aftermarket one.

How can i tell?

Is there some kind of a code on the OEM?

Do the OEM rings fit on any piston(aftermarket)?

Bore= 92.0mm.

Piston=91.5mm

I will appreciate Any help.

Thanks.

[By grayracer513, Posted December 13, 2004]

Most AM pistons for 4-strokes are set up to use the same ring sets as the OEM, but not necessarily all. Compare the cross sections of the rings and see if they appear to be the same type as your replacements.

Most Yamaha parts large enough to bear one will have at least a partial part number on them. Often this will be a 3 digit string consisting of a number and 2 letters, like 5TA which will be specific to the model of engine. For example, 5TA is for an '03/'04 450, 5NL for an '01/'02 250F. It won't follow along exactly because some parts interchange across years and multiple models, but if a number like that appears under the piston crown, odds are it's a stocker.

[By BC3, Posted December 13, 2004]

I would find it kinda strange that someone went to all the trouble to replace their piston and used a OEM piston and keep the bore STD.....

[By panosyz400f, Posted December 13, 2004]

actually the only thing that is writen under the crown is the number "3"

Any idias?

thanks any ways

[By yz007f, Posted December 15, 2004]

Your oem piston will have the stampings like greyracer513 said. I'm the bottom of my old oem piston from my 03' it's stamped 5TA Y5. So if it doesn't have the stampings on it somewhat close to that then I would say its not a oem piston.

[By MrMotorhed, Posted January 13, 2005]

who cares if it's a stock piston. measure the cylinder and put the right piston in. pistons come with rings unless it's a yamaha piston and if it is just get the rings too.

[By blue_beast_wins, Posted January 13, 2005]

The original piston out of my 01 426 says "5NG Y1" so if it dosn't say something like that i guess its aftermarket, hth.

Steve.

[By blue_beast_wins, Posted January 13, 2005]

Woops, i'm a dumb ass, i agree with yz007f