Why do valve clearances change?

[knary]

The subject sorta covers it. :)

I just adjusted the valves on my 01 1150GS. Three exhaust valves and one intake valve were off a wee bit - they were a little loose. The amount wasn't an issue, but the bike seems a little smoother when all of the same valves are adjusted to the same gap.

So why did they loosen? There's some build up of combustion deposits, wear of the parts, a tiny bit of slippage in the adjustment system and ?? What else?

[jdiaz]

Originally posted by knary
So why did they loosen? There's some build up of combustion deposits, wear of the parts, a tiny bit of slippage in the adjustment system and ?? What else?
There's a few places.....the tip of the valve follower where it contacts the high-cam pushrod face, the opposite pushrod face contacting the cam lobe, the valve follower wearing in such a fashion that it becomes ovaled on the tower it pivots on, etc. There are a lot of wear points in that system that add up to minute increases in clearance at the valve adjuster.

[dlearl476]

Originally posted by jdiaz
There's a few places.....the tip of the valve follower where it contacts the high-cam pushrod face, the opposite pushrod face contacting the cam lobe, the valve follower wearing in such a fashion that it becomes ovaled on the tower it pivots on, etc. There are a lot of wear points in that system that add up to minute increases in clearance at the valve adjuster.

Not to mention wear on the valve seats themselves causes the clearance to decrease. That's why exhaust generally tighten and intakes loosen. (Or is it the other way around?):dunno

[jdcoffman]

I just posted a question on valves in another thread should have looked around some. I adjusted my valves couple days ago in preparation of doing the throttle bodies they didn't seem to far out but when I took the bike for a ride it already seemed to be running smoother. Can a valve adjustment really make a preceptable difference in smoothness?
The first time I adjusted my valves on this bike about a year ago I found them all much tighter than what the specs called for, so much so I only loosened them up a bit just to be safe I figured how could they have been so tight. The next time I did it I went ahead and used the specs.:clap

[BMWRider]

Originally posted by jdcoffman
I just posted a question on valves in another thread should have looked around some. I adjusted my valves couple days ago in preparation of doing the throttle bodies they didn't seem to far out but when I took the bike for a ride it already seemed to be running smoother. Can a valve adjustment really make a preceptable difference in smoothness?
Yes ... an amazing difference in smoothness.

[tbdomenz]

I always think of it as (2) single cylinders turning a common crankshaft. It's as good as it gets when they are both producing the same torque/HP. If they aren't in-sync, the fun factor is dramatically diminished. With great pleasure and amazement, I once rode a R90 that was as smooth as an electric motor. An experience I'll not soon forget! I often wonder if the wrench could do it everytime or if he/she got lucky on that R90:)

[j-budimlya]

If you want to get a slightly more quantitative measurement of the effect of adjusting the valves; maybe you should look at the throttle body balance "before" and "after" you adjust the valves. You should be doing it "after" anyway to get smoooooth running operation from the valve adjustment, so just taking a look at the balance before is pretty easy. It sure makes a big change in the early peiods of engine break-in when there seems to be a lot of wearing in going on....after 20k or so miles it seems like it takes a lot longer for change to take place.....