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Quick YZ250 Power Valve Question


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On late model YZ250's, what is the purpose of the 2 light springs (item 4) & washers (item 5) on the power valve actuator shaft? If the washers were inboard of the two tangs on the valve holder bracket then I could see them serving as retainers for the actuator springs (item 1) however in the manual the diagram clearly shows them being outboard of the tangs. Enlighten me please!

Thanks.

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Edited by moleculo
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I beleive they are there as a type of antirattle set up. They also give a little bit of resistance to movement to help the valves operate smoother in a high vibration area. Be sure to check the three allen screws that go through the actuating rod. I had one come out and it made the power go flat after the bottom end hit.

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Yes, the tangs hold the powervalve tension springs in place, not the washers.

As far as I could tell when I took mine apart, is that they serve no 'obvious' purpose. They retain the washers, that's it, they are extremely weak and can barely hold the washers in place. The anti-rattle theory is interesting but I'm failing to understand how it could prevent any of the other parts from ratteling, considering the spring tension is too weak.

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I beleive they are there as a type of antirattle set up. They also give a little bit of resistance to movement to help the valves operate smoother in a high vibration area.

A vibration damper - that seems like a reasonable theory, I hadn't considered that.

As far as I could tell when I took mine apart, is that they serve no 'obvious' purpose.

Yeah, that's pretty much why I posted the question. I'm certain there's a good reason behind them being there though. I'd find it hard to believe that the ME's at Yamaha put "bonus parts" in our motors for no good reason.

Any other ideas?

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A vibration damper - that seems like a reasonable theory, I hadn't considered that.

Yeah, that's pretty much why I posted the question. I'm certain there's a good reason behind them being there though. I'd find it hard to believe that the ME's at Yamaha put "bonus parts" in our motors for no good reason.

Any other ideas?

I agree, they don't put millions into R&D just to stick in a couple of springs that do nothing.

Maybe RC has some insight???

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