Valve question

4 replies to this topic
  • BAHeron

Posted March 24, 2008 - 06:51 AM


I am in the process of changing the valves on my 2000 WR400, and i noticed the part numbers on the intake valves are different (in the yamaha breakdown). There are 3 intake valves. 2 are the same 1 is different, the center has a different number. Is it shorter or longer?:confused: and what will happen if i use 3 of the same. It seems like the valve springs will make up the difference, I may just have to re-shim? The manual shows
1 5BE-12111-10-00 VALVE, INTAKE . . . . . . . . . . . . 1 (5GS5)
2 5BE-12112-10-00 VALVE, INTAKE 2 . . . . . . . . . . 2 (5GS5)

  • Wiz636

Posted March 24, 2008 - 10:11 AM


Yes, the center valve is slightly different than the outside two. Pretty sure it is shorter, doubt you could make an outside valve work there by using a thinner least the Yamaha engineers don't think so.

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  • matt4x4

Posted March 24, 2008 - 11:51 AM


I believe you would not be able to compensate for the length difference of different valves, remember that shims are thin and vary over thousands of an inch to compensate for similar discrepancies in the valve length of the SAME valves, a different part number valve would likely be different by a lot more that a few thousands of an inch. Maybe machining a bucket to compensate for a longer valve stem might work for setting your gap, however, now your spring is no longer the right length for the longer or shorter valve stem, remember that valve springs are built to work with valves/stems of a certain length (or within a certain range) in order for the valve to have the right opening/closing rates - springs will even vary in strength between lighter titanium valves compared to ss valves (and we're talking miniscule amounts of weight here), you can't run ss valves using springs made for titanium valves as it will cause you to have the wrong spring rate (the same as setting up your bike's suspension with regards to the rider weight), the valves will not open/close at the right rate if you start to mix and match.

I hope all that makes some sense, really all I'm trying to say is it isn't just one part (shim) that would be affected by using a longer or shorter valve, there's a multitude of parts that work in unison here)

  • dirtysouth

Posted March 24, 2008 - 03:18 PM


I wonder if the center valve is smaller\larger in diameter to open up more of the chamber. Could be a couple thousandths but it will have to seal..ya know?

  • BAHeron

Posted March 25, 2008 - 05:09 AM


Well after checking and re-checking (you know...measure twice cut once theory) i finally got the right valve (or center) :confused: and yes it is shorter. Just an FYI for anybody doing this repair

I wonder if the center valve is smaller\larger in diameter to open up more of the chamber. Could be a couple thousandths but it will have to seal..ya know?

But it is the same diameter.

Thanks for the help everyone


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