Valve shim gaps -All equal or not?

Tyrell Corp wrote: ...

I think the need for the clearance is to allow the exhaust valve to temporarily heat sink into the head, hence tight clearances risks burning out the exhaust valves.

Yes! and this also applies to the inlet but less so as there is some cooling of this from the intake charge.
Valve clearances are to allow for heat expansion, Just like valve stem to guide clearance ,piston/bore clearance, shell bearing clearance etc etc etc.
If there were too little or no clearance the components would lock solid or not mate as they should at running temps causing excessive wear or seizure.
If the clearances are correct when cold they allow for enough expansion at the engines NORMAL designed maximum running temp so the components mate snugly without causing abnormal wear or indeed for the valve to sit fully on its seat when closed.
If the valve is not seating the outer thinner edge becomes exposed to constant combustion temperatures which eventually over heat the valve material causing hot spots and then damage and the same applies to the seat.
Running the valve clearances on the upper FSM limit really makes very little difference in reality to the rate of wear and the factory wouldn't specify those upper limits if there was an issue.

Okay guys that all being said. I'm adjusting the valve clearances to the middle of the spec. (.10mm is what I'm going for)
Have a good weekend

Barney

zed1015 wrote:

Tyrell Corp wrote: ...

I think the need for the clearance is to allow the exhaust valve to temporarily heat sink into the head, hence tight clearances risks burning out the exhaust valves.

Running the valve clearances on the upper FSM limit really makes very little difference in reality to the rate of wear and the factory wouldn't specify those upper limits if there was an issue.

Kawasaki Heavy Industries ...

As an aside: the 750 twins came from the factory with 0.05 - 0.10mm (.002 - .004") as the valve spec. Not long after, I read a number of places they opened that up to 0.05 - 0.15mm (.002 - .006"). I keep mine at the .003" - .005" range. I did have one that was at .0025 at the service that had walked under .002" by next check.... so I don't like running them at the tight limit.

People should keep in mind that the way they position the cams has an effect on the measured clearance.

Kawasaki specifies a cam position method that places TWO adjacent valves on the cam base circle, and the valves are to be measured in pairs.

Some people simply point the cam lobe away from the valve and measure instead of following the factory Kawasaki method. If you use this method the adjacent valve will not be on the base circle, and the valve spring will be pushing up on the cam skewing it within the cam journal clearance. Bottom line is the measured clearance will be greater than if you use the factory method (how much depends on how much wear there is in the system). Just guessing but I think it could easily be .03mm.

I just did my valve adjustment. All but three were in spec. One exhaust was a tight .002. #2 exhaust was less and I had to go down two sizes to get .004. #2 intake was tight, 0 clearance. All this happened within 4000 miles. I should have checked them sooner. I had noticed my mileage had dropped off and that should have given me a clue. I should have listened to myself. :pinch:
Steve

In a DOHC engine the valve clearance increases as the valve heats up. The head of the valve expands and that draws the the valve further into the combustion chamber when it is resting on the valve seat. The stock camshafts in these old engines have very long opening and closing ramps so running the valves at the maximum factory clearance will not harm them in the least. Running the clearance at the maximum will make starting easier and will also make the idle smother.

+1 I agree, using the FSM procedure by checking two at a time gives not only more consistent readings but is also quicker.

Either way you are reading the base circle clearance on the cam.

On the 550's, the valve clearance definitely gets smaller as the bike is run hotter on the highway. If the clearance is out of spec, it will stall after a highway run. It will restart and run if you keep the throttle open enough. Then, after cooling a few minutes at slow speeds, it will run fine again. No two ways about it. The stem, being the longest dimension, makes the most difference, at least in the case of the 550.

80B4 wrote: In a DOHC engine the valve clearance increases as the valve heats up..

NO! Totally wrong.
The clearance reduces when hot.
The valve stem also expands and lengthens when hot and its total expansion is greater than the valve head.
If the clearance got wider when hot there would be no need for clearance when cold.

These engines must have valve clearance when cold because they will not start if there is no clearance when cold.
The head of the exhaust valve is the hottest area in the engine (hot enough to glow red) and is only intermittantly cooled when it is resting on the valve seat. The stem is cooled by its constant contact with the valve guide and it's operating temperature is 600 to 800 degrees less than the valve's head.
The thinking that valve clearances tighten up due to thermal expansion is a hold over from OHV engines that used long pushrods to open their valves.

Hmmm, not really with you there.

I am still of the opinion that steel (Valve stem) expands more than the aluminum head when heated.

Regardless if it’s OHC, DOHC or Wankel for that case.

Valve clearance will decrease when the engine is hot, must say that I have had opportunity make some empirical studies in the subject on my track bike during my racing years.