Possible tight valves


6 replies to this topic
  • Yamiryder

Posted June 21, 2011 - 06:08 PM

#1

I'm curious if tight intake valves would cause hard starting when cold but normal starting when hot. This is an 07 450 by the way.

  • grayracer513

Posted June 21, 2011 - 06:12 PM

#2

Yes, they will.

  • dvn

Posted June 22, 2011 - 03:15 AM

#3

I'm curious if tight intake valves would cause hard starting when cold but normal starting when hot. This is an 07 450 by the way.


I think it's the other way around. Hard starting when hot. Have you checked the valves?

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  • bmeador

Posted June 22, 2011 - 03:24 AM

#4

No, Gray is right as usual!!

  • Yamiryder

Posted June 22, 2011 - 04:54 AM

#5

Nope, haven't checked the valves yet. I thought maybe my intake valves were tight and it sounds like I was right.

  • grayracer513

Posted June 22, 2011 - 06:47 AM

#6

Why don't you simply check it?

From direct experience, I can tell you that tight intakes will cause a bigger drop in compression when cold than when hot. This is for a couple of reasons, not the least of which is that the valves are tighter when cold than when hot. The logic of one dimensional thinking tells us that the valve expands when hot, so the stem gets taller, and the clearance is less when hot. Makes perfect sense, and it's often true of big engines with cast iron heads. But looking at the complete picture, the head is aluminum, which expands at a significantly greater rate than titanium does, and the head casting controls the distance between the valve seat and the cam.

Because of this, an engine that, when cold, needs a .05 mm smaller shim just to close the valve, and has so little compression that it has to be push started, can warm up and have pretty normal cranking compression once it's hot.

If, however, the bike has good cold cranking compression, valves are probably not the root of the problem. But checking them is a lot more productive than worrying about it.

  • Duner185

Posted June 22, 2011 - 12:31 PM

#7

Why don't you simply check it?

From direct experience, I can tell you that tight intakes will cause a bigger drop in compression when cold than when hot. This is for a couple of reasons, not the least of which is that the valves are tighter when cold than when hot. The logic of one dimensional thinking tells us that the valve expands when hot, so the stem gets taller, and the clearance is less when hot. Makes perfect sense, and it's often true of big engines with cast iron heads. But looking at the complete picture, the head is aluminum, which expands at a significantly greater rate than titanium does, and the head casting controls the distance between the valve seat and the cam.

Because of this, an engine that, when cold, needs a .05 mm smaller shim just to close the valve, and has so little compression that it has to be push started, can warm up and have pretty normal cranking compression once it's hot.

If, however, the bike has good cold cranking compression, valves are probably not the root of the problem. But checking them is a lot more productive than worrying about it.


This is some great information, Thanks you have helped me out.





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