Powervalve Fix?

[jakeyz250]

I read a post on here where somebody said something about a special fix that has been done to keep the powervalve from hitting the piston. Can somebody please tell me about it? I believe my powervalve has started hitting, and I am probley going to end up trying different things to fix the stop tabs. But I would like to know of the other fix as well. Thanks :aj:

Oh yeah, how much pressure is put on the stop tabs?

 

[cr2504life]

I have no experience with the yz valve but i have heard that can file down pv on my cr, expecially if you bore the cylinder. just a thought though

 

[jakeyz250]

Does anybody know what happens when I take out the allen bolt on the left side of the engine, in the power valve stop tab area. Will something come lose inside, and fall down the cylinder. Would it be best if i just took it apart?

 

[DougRoost]

I sure hope you have a shop manual and know what you're doing on that mechanism, especially since you haven't told anyone on this forum what year/model bike this is!

My main suggestion would be for you to call Eric Gorr before doing anything. He just fixed me up on my KTM 300exc and knows all the nuances of these different engines better than anyone. Click the link off to the left and you'll be able to find his number.

 

[Rcannon]

What year specifically are you talking about?

The powervalve on my 97 is fairly simple. I had a local machien shop grind some of the powervalve away to stop it from hitting. I considered this a temporary fix as it really just covers for worn out parts. It is not enough to just replace the powervalve. You also have to replace the cover.

There are two locating pins that could come loose. I cannot imagine them falling in the engine, but I suppose anything is possible. If you unscrew the hex bolt, the powervalve splits in two.

Fogure 150.00 for the powervalve, cover, and new gaskets. You will also need to replace the piston and rings. The job is not too difficult, but please use the first 25.00 or so to buy the manual. C-bay has a lot of the factory manuals for sale.

 

[jakeyz250]

Well, like the info by my name says, "1990 YZ 250" ... And I don't see any wear on the piston, and the piston and rings are pretty new. Do I really need to replace them.

 

[Rcannon]

I would only replace the piston if it were damaged. BUT.....you were asking about the powervalve hitting things. It really cannot hit anything but the piston. If it does not hit , your ok.

My 97 had a polished mark on the front of the piston where the powervalve was rubbing. It was an obvious problem. There was also an audible "click" as the valve would close.

 

[jakeyz250]

When I slowly turn the motor over by hand, i watch the little arm on the right side of the engine that is connected to the pv. It moves slightly. I don't have the pipe on or a sparkplug in. Does that probley mean that its hitting, or is that what it does? Thanks

 

[jakeyz250]

Do you know when yamaha fixed this problem, or does it still happen to the newer yz's.. I think I will just fix this problem, then sell it.. and buy a newer bike,

 

[Rcannon]

The 99 and up bikes do not do this. The powervalv eis completly different. I would not let the problem keep me from enjoying one of the older bikes. All bikes have parts that wear out. I worked on an old 82 yz 250. The bike had long ago worn out. The powervalve was still working. This link has a decent drawing of the powervalve in your bike. http://63.164.134.66

The arm your talking about will move up and down. Most of the movement shoudl happen at higher RPM's than kicking speed.

That arm is what opens and closes the powervalve. In their drawings, Yamaha calls the powervalve the Governor.

 

[jakeyz250]

The powervalve is not the only reason I want a newer bike. I want a newer bike that doens't have many mods on it so I know what all has been done. This 90 yz 250 has so many problems that I find. The person i bought it from didn't believe in warming it up at all. As soon as he started it, he would take it down the highway at full throttle. Then he wonders why it seized twice. He used a vw brake hose for the back brake, which didn't have the same fittings, so he welded them together. The bike has a much nicer life now that I have it.!!
I also have an 1982 yz250, and that is a very nice running bike. I bought a new spark plug for it when I first got it, and i used it for a couple years. Then I got the 1990 yz which had a terrible plug in it, so i switched them, and the plug fouled after a few rides.

when i turn the engine over, the arm moves only slightly,

 

[Rcannon]

I just checked mine to make sure I was not mis-speaking. There is no movement when kick starting the bike...none.

I suspect yours might be gummed up. The whole mechanism is pretty simple and would not be tough to clean, but get a manual for this! There are abotu 40 loose parts to the roller bearing. Getting them back together takes 4 or 5 hands at best.

 

[jakeyz250]

So I should really get a manual? Jk, haha... Ok I will get the manual probley tomorrow, or get it off of cbay.

 

[Rcannon]

Hey, why not get a manual....

If possible, try to find the original Yamaha book. The Clymer one works, but when the proofread the book they get really drunk, smoke pot, and take pills. There are errors everywhere in it!

I have bought a manual for the 97 and 98 YZ. I dont think I paid over 20.00 for either one.

 

[jakeyz250]

I have a manual for my 82 xr200r, i'm not sure if its clymer but i know its not the original factory one, and halfway through the book, it starts over!!!, Its exactly the same. But i do have the factory manual for my 82 yz250, and it isn't translated perfectly either, but at least it doesn't start over!!! Hahaha....

Thanks alot Rcannon

Oh and the powervalve is making a shiny spot on the piston now!

 

[DougRoost]

Will you PLEASE call Eric? Quit guessing, quit wondering, and just call the guy who knows this stuff.

 

[jakeyz250]

I'm not guessing now, I know its worn out...