Power Valve wasted? YZ250 89 Pics inside.


Hello everyone! I'm new here (new to MX and also to this forum) so just a quick greeting from England, London (Kent)! :thumbsup:

Ok, so i've taken on what some would consider a handful for my first project bike... an 1990 YZ250 (1989 Engine) Im part way stripping down my bike and i've come across (what could be) my first problem, a chipped power valve?

See pictures below.



now.. i assume this is some kind of stone chip and is not a good? Weirdly the bike was running prior to the rebuild so im unsure what to think. I assume performance would have been effected? The head is showing no signs of damage nor is there any damage to the piston! What do you guys suspose happened?

Everything seemed to be going so well until today :lol:

Are there any kind folk have a spare power valve doing nothing? I get the feeling this part will be hard to find as it's almost 22yrs old! :)

Bike so far.. (head has been removed since this picture was taken)


Any help appricated peeps!

The power valve is ok.

It has chipped from the side that is facing away from the piston.

Just check that there aren't any sharp edges (where it broke) that could seze the valve. Also clean the valve and check its smooth movement in cylinder.

My preliminary thought is that someone wedge something in the exhaust to prevent the valve from spinning while taking the bolts loose to remove it. right wrong or indifferent I always use a wooden hammer handle for that but I can see someone trying to jab a screw driver or something to do that.

I would use it if moves freely in it's bore and doesn't interfere with the piston when it the close position.

Mat & Jsantapau - thank you both for your replies.. I've got no choice but to re-use the part in anycase as i cant find another anywhere. I feel less apprehensive now you both have confirmed what my dealer already told me today. If the perfromance impact is minimal then i'll carry on using... after all it is 20yrs.

Jsantapau - i have no doubt you are correct... i too used a woodern hammer handle to wedge the valve stationary. The valve spins clear of the piston and rotates in its bore without issue.

Thanks again for your help (both of you)


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