1971 r75 /5 Valve clearance opens up fast

[submerge]

Hi. I'm new. So..
New to me, 1971 R75/5 - Left side intake rocker/valve is very loud. The bike is new to me so I'm checking valve clearance and fluids etc. before I ride. Left side valve clearance has opened up quite a bit, making the loud noise. Rocker arm is good, no excess movement, pushrods centered and not warped. Adjust clearance to spec, reassemble. 2 miles down the road the noise comes back. Check the clearance again and the intake has opened way up, almost to far to adjust back into spec. ? I have searched around and many people say that rapidly closing clearance is a problem, what about the reverse?
Thanks all!
Wyatt

[schrader7032]

Wyatt -

I read this on another forum and have been thinking a little about it. You're right...we all hear about them closing up. I'm assuming that you're getting the nut holding the gap tighten enough and that it's not coming loose. They don't need to be torqued down to a specific number...I've always found it fine to just get them a good snug kind of tight. Are you beginning to loose the adjustment range on the rocker arms? If they are indeed getting this loose that quickly, it won't be long before you can't do it anymore.

Things that come to mind are that the pushrods are somehow collapsing. I don't the dimensions of them, but if you were to remove one from each side you could compare the lengths. You said they're not warped, so you must have removed them at some point. Could the cam followers be collapsing? I've not heard of that before, mostly just the faces shed material. But if they were deforming, that would explain this.

What about your head bolt torques? Have you checked them? It's possible that your head bolts, the 4 that hold the rocker arms in place, are pulling out. If they don't hold their torque any more, then the head begins to move away from the base of the engine, thus creating more clearance. I forget which one it is but IIRC, it's the upper left one as you look at each cylinder.

If the head bolts are pulling out, you'll need to completely disassemble the top and and do a helicoil repair. BMW sells a kit to do this. It also requires a special tool to ensure that the hole is drill in perfect alignment with the other studs.

[submerge]

I checked all the torques, they seem to be fine. I didn't remove the pushrods, just spun them while seated in the adjuster and didn't notice any movement that some warpage would show. Not a very refined or precise way, I know. I posted a pic on the other forum, you can see how far out the adjuster is. I feel like I'm just missing something really obvious. The rockers are not moving up and down or twisting at all, they seem to fine and moving freely.

[schrader7032]

I saw the picture on Boxerworks. Others are also thinking pulled stud. You mentioned that the torque was a little loose but not too bad maybe a little loose. Did you slightly loosen each nut and retorque with a moving motion to 25-26 ft-lbs? I don't know if this translates to the head bolt torques, but it doesn't take much motion by the rocker arm nut to change the gap of the valves. So, I'm thinking if you had to retighten the head bolt torques by say 1/4 to 1/2 turn, that could mean quite a difference in valve clearance.