R100GS Rocker Getting Tight

I have an odd problem on my R100GS. This is actually an R80 top end BTW. The right side exhaust valve rocker keeps getting tight vertically. The heads, valves, and cylinders are all in good shape. The problem was noticed by a mechanic recently when we did rings. It was tight, almost no vertical play, when we took it apart, but we both assumed that when everything was put back together right, by someone that knew what they were doing, the rocker would retain the vertical play that we gave it. But within a few hundred miles, doing the first re-torque, it was tight again. I have loosened it repeatedly, and it always gets tight again. Nothing else is out of order. The studs are fine, holding torque, and the valves are not changing adjustment.

Here's the situation. The one rocker only tightens to the point that when you go to set the valves, there is almost no perceptible vertical movement. There is no "click", but I can see it move, and it does move enough to pinch the oil film. There is always a pool of oil in both sides of the rocker cover, and the rocker itself is clearly getting oil. When the valve adjuster bolt is loosened, the rocker pivots freely, you just can't keep the right amount of vertical play in it. It seems to go back to the same level of tightness and then stay there.

Has anyone ever had this problem before?

Thanks

Is the vertical tightening enough to restrict movement of the rocker arm? It would be interesting to know that if you backed off the valve adjustment a bunch, could you easily swing the rocker arm through its movement. If so, then maybe it's a non issue. You don't want any clicking when the rocker is moved up and down...only just a minor movement in the oil film where the rocker meets the pillow block.

Do you have the shim-type rockers? And if so, have you been changing the shims?

20774 said:

Is the vertical tightening enough to restrict movement of the rocker arm? It would be interesting to know that if you backed off the valve adjustment a bunch, could you easily swing the rocker arm through its movement. If so, then maybe it's a non issue. You don't want any clicking when the rocker is moved up and down...only just a minor movement in the oil film where the rocker meets the pillow block.

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When the adjusting bolt is loose the rocker moves freely.

AntonLargiader said:

Do you have the shim-type rockers? And if so, have you been changing the shims?

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No shims.

I should mention that this bike is generally under the care of my brother who has been working on Airhead BMW's for 50+ years, and IMHO is one of the finest pre-1995 BMW techs in the country. I do the maintenance, but get my instructions from him. He has never seen this before and is currently thinking about possible reasons for this behavior. I just thought it wouldn't hurt to throw it out here too and see if anyone had encountered this issue. So far, the answer seems to be know. I appreciate all the input.

I think many airhead owners have witnessed spreading outwards of the relatively "free to shift" rocker pedistles.
Not sure what arrangement of parts you have, as there are several reiterations over the years.
Regardless, the area that the pedistle or disc seat sits in the aluminum head may be slightly uneven (seat damage alowing less than parallel support and hence inward migrating force that allows creep and change to the spacing established. In that case, slight loosening of the head retention nuts would lead to slightly looser rocker shaft end float generally.

JNCLEM said:

When the adjusting bolt is loose the rocker moves freely.

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Then I'm not sure there is a real problem...other than not knowing the reason why this is happening.

20774 said:

Then I'm not sure there is a real problem...other than not knowing the reason why this is happening.

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I think that's where we are at this point. It simply isn't right, but since it is getting oil, and seems to move, maybe no harm is being done.

R100RTurbo said:

I think many airhead owners have witnessed spreading outwards of the relatively "free to shift" rocker pedistles.
Not sure what arrangement of parts you have, as there are several reiterations over the years.
Regardless, the area that the pedistle or disc seat sits in the aluminum head may be slightly uneven (seat damage alowing less than parallel support and hence inward migrating force that allows creep and change to the spacing established. In that case, slight loosening of the head retention nuts would lead to slightly looser rocker shaft end float generally.

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So you are saying that you would reduce the torque on that rocker? Or all four on that side? By what, a pound or two? Just wondering.

R100RTurbo said:

In that case, slight loosening of the head retention nuts would lead to slightly looser rocker shaft end float generally.

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You'd of course loosen the nuts on the other two studs as well to keep even cylinder head torque all around. Then, of course, you'd likely have a head gasket leak, as it was previously compressed by the higher torque. The o-ring at cylinder base could leak for same reason, too.

The absence of the plastic shims means these are old heads on newer bike. Like for example heads from an '83-'84 R80RT, subject to valve seat recession if not previously retrofitted with new seats/valves.

The original R100GS rocker arms used shims for end float adjustment.

I think you could fit new-style rocker arms and use shims to adjust them how you want them. First, however, I'd inspect the exhaust valves looking through the exhaust ports to verify they still have their proper seat faces and are not receding. Often tightening exhaust valve clearance is the classic symptom of recession. It's something that has to be fixed before the valve loses it seat face altogether, as when that happens the valve becomes loose enough that the keepers fall off and then the valve hits the piston.

JNCLEM said:

When the adjusting bolt is loose the rocker moves freely.

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Since there's supposed to be some valve clearance it should move freely with the adjusters tightened. In fact, tightening/loosening the adjusters should make no difference at all as long as there's always clearance.

There is no issue. If you have the older rockers, and you have free movement with a slight bulge in the oil film when you try to slide them up and down, you're fine.