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98 YZ250 compatibility?

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Hi guys,

This is my first post in the Yamaha forum. I'm usually in the Kawasaki 2-Stroke.

I just picked up a '98 YZ250 motor and I have a few questions. What year motors are the same style as the '98. I have done a little research and found that 97-98 are similar. I'm not sure how accurate the info is though.

What year cylinders will fit on the '98? Are most of the YZ's the same size bore?

If I were to do a top-end on this motor, do I have to get a '98 kit or are other years the same? Looks like '92-'98 pistons are the same. Are the cylinders compatible? Can I replace the '98 cylinder with any one from '92-'98?

I am very familiar with similar years of KX's, but I'm new to the Yamaha's so any info is much appreciated.

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OK, I just got a 94 YZ250 cylinder. From what I've read, it will bolt up to the 98 bottom end. Only issue I see is the pipe and maybe gaskets. I've heard of people using the 94 cylinder before. Anyone ever done this?

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Lots of pro racers used to run the 94 cylinders back in the day on the newer yz's in that year range (not sure exactly what years this was done through however)... so it must be pretty distinctively better than later years.

Maybe RCannon will chime into your thread. He's pretty darn knowledgable when it comes to the older Yz's

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Did it with a 95' top & bottom in a 98' frame. I think the 94' & 95' are the same. Only issues I had was I had to use a 95' pipe, and a different reed cage (95' is 4-bolts, 98' is 5). The swingarm pivot bosses in the back of the bottom end were different by 1mm. (But that doesn't matter since you have the 98' lower). Powervalve components appear to be identical to the 98' too. Be sure to Blue Loctite the PV actuator rod bolt when you install the new cylinder. Bad things can happen if it backs out. :smashpc: (New PV and a top end)

Good find, I've read also that the 94' was the jug to have. 96' is the oddball in the group. Yami's first attempt at the newer style powervalve.

My only complaint with my 98's are the pressed-in float valve seat in the PWM carb. No way to replace just the seat if it starts leaking, gotta get the whole bowl.

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The 97 and 98 were basically the same except primary drive ratio. Its changed enough that final drive gears sized the same will not work well on the 98 even though they were perfect on the 97. The ignition black boxes exchange between the bikes. The 98 box runs better in the low-mid area where the 97 box is a top end only thing. Actually, you'll never get good low, mid and top from these engines. Pick any two and be happy.

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