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christrucker

wr400 valve adjustment question

8 posts in this topic

Hay guys, beleive it or not, this is the first valve adjustment that I have done. Its a 99. I bought it new, and it runs great. I just noticed that the power is starting to lack, and I can kick it now without the compresion release. One question is, can the valves be too tight? I figured the gap would be to big from them wearing, but the fealer guage seems tight on the factory specs. Actually it won't slid under the cam. Am I missing something here, or do they wear and get tighter, so I would need a smaller shim? Thanks.

-Chris-

:)

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Your lash will be tighter because the valve stem will stretch in time. Yes, you will be able to push the kicker with ease because the valves are not fully seated. Have your valve lash fixed and you'll be surprised of the power gained. :)

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Take immediate action and adjust those valves. Flame is correct that the valves will tighten up over time with a shim under bucket valve train design. I believe it is due more to the valve seat/valve face wear rather than the stem stretching, but the net effect is the same. If valve adjustments are ignored on these bikes, serious damage to the head (valve seats and/or head cam journals) will ultimately be the end result.

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Lucky for you the ol' 400's had steel valves.

They get tighter because the valve face wears, as does the valve seat. The valve literally bores it's way into the cylinder head, closing the clearance up.

Sorry to break the bad news, but stem stretch doesnt cause the clearances to close up :)

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Lucky for you the ol' 400's had steel valves.

They get tighter because the valve face wears, as does the valve seat. The valve literally bores it's way into the cylinder head, closing the clearance up.

Sorry to break the bad news, but stem stretch doesnt cause the clearances to close up

This is why they tighten up.

Better hope you didn't burn any valves.

Why the hell have you not checked the clearences before?

It is very easy to do and only takes a half an hour.

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Bike always ran good, so nevery thought It needed it. Guess its because I had xrs growning up and nevery really had to adjust those. The first 3 or so years I had the wr, I didn't use it to much, but last year I put alot of miles on it, and have done 4 different trails this year at about 40 miles a peice. Is there a way to check and see if there is any damage to the top end? Compression test after I get the valves adjusted?

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I would do a before and after test. I don't think you have any damage just a tight lash. After adjusting three different Yamys I have found that .006 intake and .010 exhaust are the best numbers, valves seal well and no tapping noise when the motor is at running temp. :)

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Is there a way to check and see if there is any damage to the top end? Compression test after I get the valves adjusted?

After adjusting the valves try and kick it through without using the compression release. If it runs fine, leave it alone and enjoy your ride . Compression testers are useless. To get a good indication you can use a leakdown tester (fills the cylinder with compressed are and measures how much leaks past the rings and valves, displayed as a %)

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