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CRF450 Valve Questions

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Posted by: Zero---------------------

I have a few valve questions here.

1. What is the "norm" direction for a valve to go out of adjustment. The exhaust valve spec per the manual is .011 +/- .001

If I get a reading of .014 this would be considered loose, right? Is this a normal wear indication for an exhaust valve? Or do they normally wear the other direction? Is it the same for intake valves?

2. I have read that hard starting bikes is an indication of the out of spec valves, does this mean exhaust or intake or either?

3. What causes one to go out of adjustment over the other?

My rocker arm came in at .020 before adding it to the .012 of my right exhaust reading, which seems to be WAY outr of adjustment also.

My left exhaust valve came in at .014.

(both intakes were spot on)

Is this normal? I dont see anyone mentioning they have probelms with their exhaust valves?


Posted by: Rich Rohrich---------------------

Quote:
Originally Posted by Zero
I have a few valve questions here.

1. What is the "norm" direction for a valve to go out of adjustment. The exhaust valve spec per the manual is .011 +/- .001

If I get a reading of .014 this would be considered loose, right? Is this a normal wear indication for an exhaust valve? Or do they normally wear the other direction? Is it the same for intake valves?


Yes this is normal for the steel exhaust valves. The intake valves are coated titanium and the clearance gets smaller as they wear.

Quote:
2. I have read that hard starting bikes is an indication of the out of spec valves, does this mean exhaust or intake or either?


On the CRF450 it's generally a result of intake clearance closing up, or the decompressor going out of adjustment.

Quote:
3. What causes one to go out of adjustment over the other?


The intakes suffer from valve face recession issues.

Quote:
My rocker arm came in at .020 before adding it to the .012 of my right exhaust reading, which seems to be WAY outr of adjustment also.

My left exhaust valve came in at .014.

(both intakes were spot on)


Keep in mind that the rocker has a 1.9:1 ratio . The exhaust clearance should be measured directly above the shim;. Anywhere else won't give you accurate info.

Quote:
Is this normal? I dont see anyone mentioning they have probelms with their exhaust valves?


Yep it's normal. Steel valves wear a little over time, everything does. Guys who run pump fuel or cheap race fuel with a lot of random junk in it will find that the exhaust valves on the CRF will pit and destroy the face over time, but they still are much tougher than the titanium intakes.



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