Valve Theory 101

[Pterodactyl]

If the clearances are set too wide then the valve lift and duration will be (slightly) reduced. This will slightly reduce the peak power available at high rpm, but as noted earlier can make the engine run smoother and stronger at lower rpms and mid range.
Too loose is a far safer situation, and valves on modern engines with shim under (hardened) bucket followers, like the FJR, tend to always wear in a way that reduces the clearances, which is one of the reasons why many folks will set their clearances to the wider end of the spec range. It also prolongs the need to re-shim, perhaps never requiring it again during the lifetime of the engine.

This is what I did last winter. We'll see if I ever have to replace a shim again.

Thanks for the info to those who have responded.

 

[PapaUtah]

I checked the valves on my '05 at 30K and 60K. I traded it off with 82K. Between 30K and 60K I had 3 of the 8 exhaust valves that moved .02mm from the 30K values and 2 of the 8 intakes that moved .01mm. Radman couldn't detect a change in the others. He was a good mechanic. I took his word. Everything was still in spec at both checks with the closest being 2 exhausts within .03mm of the limit. We buttoned it back up and I never had a problem and it felt fine and made no noise at trade in. Only thing that was ever done to that bike was a CCT at 50K courtesy of Y.E.S. and the TPS recall. Oil changes every 2,000 and gas it up an go.

 

[HotRodZilla]

Oil changes every 2000??

 

[Fred W]

Yeah, send me that used oil, would ya. It has another 3k miles left on it.

 

[bem136]

What is the lowest limit of clearance for a valve before it start to burn or give problems ??

When the valve no longer has any gap you are at the critical tipping point. Once there is *any* wear after the zero gap point the valve won't fully close letting burning combustion gas leak around the valve flute and that's going to be the end of the valve very quickly. One tip-off the exhaust valve clearance is getting very tight is improved high rpm performance because the exhaust valve is open longer with higher lift. Hopefully there is enough valve/piston clearance that the early opening, high lift valve won't kiss the piston.

Just a comment on the higher lift, it is my understanding that on modern bikes that a higher valve lift by itself will not really improve performance with the exception that you are changing the valve open and close times. Any higher lift of the valve does not guarantee more flow through the valve port as the flow is not a linear function and increases very little at or near full lift. Rather a quicker rise of a valve would have a much more significant effect on performance as it opens the area for initial airflow sooner within the cycle. I understand that is the advantage in having two smaller valves rather than one valve with the same total flow capacity, the rate at which flow area opens on initial lift, in addition to weight and spring size advantages of course. I would guess there may also be some advantages to the smaller valves in reducing free radicals in the combustion chambers and intake mixture distribution.

 

[ionbeam]

^^^^ Which segues into seeing the valves as just part of a larger system from the air box intake horn to the tip of the exhaust as a resonant tuned power system which is engineered for specific volumetric efficiency at specific rpm bands.