250r motor experts only

[drthrottle]

I have a motor w/serial numbers on the case that indicate it is an 89 250r. I tore it down and it has a piston that measures 67.5mm. (Stock 89 bore is 66mm) The piston has "STD" stamped into it. The other numbers on the piston indicate it is an 86 TRI Z piston. There is also a .200" inch or 4.8mm spacer plate under the cylinder(not stock on 89 250r). What the hell do I have. I need to rebuild so I can sell with peice of mind, but I don't know what I have to replace this stuff with. Help would be nice.

[bigbadktm]

there were 2 different cylinders from what i have heard; a and b, one bigger, one smaller. post this question in the atv tech on glamisdunes.com . there are lots of wiz's on that site that can point you in the right direction.

[velocityatv]

the (std) is stamped on most wiseco pistons so don't swet that.

I don't think you have a tri z piston I went to wiseco web site and the tri z stock bore is at 68mm so that isn't going be right.

Sounds like someone built a spacer motor.
The thing is the 86 piston pin highth is taller than the 87-89 motors. You have to use a 4.5mm spacer to compensate for the taller piston. Look at the intake and see if there are 2 strips of metal running up and down in the middle of the opening. If there is I believe you have a 87-89 jug if not you have a 86. I'm willing to bet you have an 86 jug and piston. To fix this you'll just need to have it bore and honed and get a 68mm piston for a 86 and some gaskets. Don't forget to get an extra base gasket to go with the spacer plate.:devil:

[drthrottle]

I have the 2 strips in the intake so 89 jug. I read the stamping off the piston to CJ racing and she said TRI Z. The piston is stamped like this:
[EXHAUST]

B00C2

STD
515PS
CD
(ARROW DOWN)


[INTAKE]
Thanks velocity, you're in the know but there's more to this mystery motor. Keep it in mind if you would please.

[velocityatv]

Thanks for the part #'s I think I got it figured out.

The max bore for a 87-89 cylinder using a stock piston is 68mm if you want you can still bore a few more mm more than that but you would have to use a different piston. If I look up the piston # you gave me at wiseco.com its a 69.25mm tri z or IT 250 piston. I know on the long rod motors you can use a 86 piston or a YZ piston if you max you bore and want to take it a couple more over. You than have to use a spacer. Because of the pin highth. That would make sense. Sounds like someone maxed out your bore and took it a little higher. As long as you don't go too much higher on the bore you should be fine. If it gets to large your cylinder walls could crack due to being thin. You should be able to take it to 69.5mm without a problem. If you liked the way the motor ran I would just put another tri z piston in it. If you wanted to, you could just put a 86 piston in it. The max for an 86 is 69.5. The problem the TRI Z piston might cause is that it could weigh diferent. In two-strokes a balanced assembly is key to long life of your motor. Also the boost port could be shaped different, that could be good or bad, depending on the shape and timing of the port work.
Hope I helped:devil:

[Teufel]

Hey Bro, want some good 250r info??? go to www.macdizzy.com

Teufel

[deathman53]

for years I think duncan racing used yz pistons(same as tri-z), they started at 69mm, the correct spacer for the 86 piston and 87-89 rod is 5mm, for the yz it is a smaller spacer plate. you are pretty much maxed out, the biggest you can get for a r is 140 which is 69.5mm.