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shimming?

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Hey guys, picked up my 04 yz 250f in july of 04 out of the crate, and now being it is filled with snow here in MN it is time to check my valve clearences. I just have one question, when you are shimming the valves, what exactly is it that makes them needed to be shimmed? Are the cams getting worn? I don't wanna sound dumb, :cry: i would just like some knowledge about this subject.

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I just have one question, when you are shimming the valves, what exactly is it that makes them needed to be shimmed?

three things conspire to require periodic shimming:

valve stem stretching, valve head tuliping, and a combination of wear on the seat + valve seat receding.

n.b.:

at 12,000 rpm a given valve is opening 100 times a second. something's gotta give.

ps

make sure to check out the 250F FAQ:

http://www.thumperfaq.com/sitemap.htm

jim aka the wrooster

'01 wr250f

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thanx alot you said it straight to the point

oh and one more thing, i have heard about these kibblewhite valves and springs, i hear they are stainless and pretty reasonabled priced around $375. Is this correct? Should i drop my titanium valves for stainless? Are they an improvement over stock? Are the rumors true that stock life expectancy of valves are only 30-50 hours compared to kibblewhite at 300 hours

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i have heard about these kibblewhite valves and springs, i hear they are stainless and pretty reasonabled priced around $375. Is this correct?
Should i drop my titanium valves for stainless?

no. use OEM yamaha titanium valves -- highest quality, longest lasting.

Are they an improvement over stock?

no.

Are the rumors true that stock life expectancy of valves are only 30-50 hours compared to kibblewhite at 300 hours

some honda CRF250 owners have experienced extremely short OEM titanium valve life. installing replacement OEM honda titanium valves in some cases did not solve the problem, leading to another top end teardown in short order. kibblewhite, among others, have come out with stainless steel valves for the hondas, and there are reports over in CRF-land that these give markedly longer life than the OEM titanium honda valves.

instead of retyping that paragraph, i'll just ask you to read it again but substitute "kawasaki" and "KXF" wherever you see "honda" and "CRF".

that said, yamaha's valvetrain, including the stock titanium valves, has proven to be the most reliable setup going. there are many folks, me included, who have thousands of miles and many hundreds of hours on their 250F's with few or no valve adjustments. the OEM yamaha valvetrain components work and are very reliable -- it's that simple. don't futz with it.

jim aka the wrooster

'01 wr250f

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no need to change yours if they are not worn.

i have the 638th bike off the assembly line in '01.

yes, it is 4+ years old now.

original valves, original clutch too.

shimmed 3 times now.

i'm probably over well 300 hours with the original valves.

that figure is mostly for red/green/yellow bikes.

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i have the 638th bike off the assembly line in '01.

steve has me beat by a few hundred bikes.

i own the 801st WR250F made in '01. original valves, 4K miles.

jim aka the wrooster

'01 wr250f

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