Help with piston

[250R_SV]

I opened my top end yesturday to check piston and rings for maintanence. I have never opened this engine, it is as I bought it. As I expected rings need to be changed, piston is in good shape. I want to buy the rings but the piston has no serial or number part in the top. There is only a W engraved at the top of the piston.
Piston seems to be 68mm(265cc)
Will appreciate any comments.

Regads,
Guillermo

[250R_SV]

My trx is 1988.It has a long rod, and thicker gasket at bottom cilinder. Do you think its a 86 piston?

[265 sleeper]

Any stamps on the under side of the piston? You might just need to clean the piston off . Hard to say without pics. Does the piston have a half moon on the bottom of the intake side (86 style) or a rectangular shape below the rings (87+ style) .

[250R_SV]

Found some numbers in the inner part of the piston:
5127 on one side and 3XK01 on the other side.

[250R_SV]

piston

[265 sleeper]

I might be wrong it could ether be a yz piston. Or a 86 style piston.

[265 sleeper]

Looks like someone ported that piston on the side

[mx91a]

My guess would be a YZ250 piston, 68mm is the stock bore for late 80s and 90s YZ250s. Notice how the exhaust skirt is flat on the bottom with sharp corners, the TRX piston has large radiused corners on the bottom of the exhaust skirt. Also the exhaust skirt is close in length to the intake skirt where the TRX/ATC piston has an exhaust skirt noticeably longer than the intake. Here is a picture of a YZ250 piston for reference:
http://i97.photobucket.com/albums/l209/mx91a/My%20Documents/yzpiston.jpg

[250R_SV]

looks similar ! only difference I can see is the hole other hole in the wristpin whole.
Im trying to find rings for this piston.
Any advise?

[265 sleeper]

can you take a pic of the ring 250rsv and same with mx91. see if the ring gap the same style. mx91 what brand piston is that you got

[mx91a]

Originally posted by 250R_SV
looks similar ! only difference I can see is the hole other hole in the wristpin whole.
Im trying to find rings for this piston.
Any advise?

Yeah it looks like the piston I have has an extra hole for prying the circlip out. Mine is a 90's style piston made by ART who I believe is an OEM for Yamaha. Yours may be the 83-87 style. If your piston is a cast OE style, which it looks like it is, you can get rings through Yamaha or anyplace that sells PRO-X replacement rings. I have two sets of LA-Sleeve/PRO-X replacement rings on my desk now for YZ250 pistons. One set is for 83-87 pistons and the other for 88-98 pistons. The only physical difference between the rings is their thicknesses with the 83-87 being thinner at 0.96mm than the 88-98 at 1.18mm. Hopefully this can help you determine which year set your piston is if you measure the thickness of your rings.

[250R_SV]

Thanks
I'll measure the rings and take a picture of it.

[250R_SV]

top of piston. notice the letter W

[250R_SV]

side view

[250R_SV]

today I checked rings from a 1990 yz250 STD and the seem a little thinner tha the ones in the piston

[250R_SV]

Ok guys, so I couldnt find for sure the piston brand, so I measured the piston, bought some thicker rings and machined the pinston's grooves for the rings to fit, worked fine!