Loose cylinder head stud? Is this normal?

[Doug-504]

1989 BMW R80RT

Checked rocker end play this weekend after valve adjustment still resulted in noisy Tappets. Excessive play found on 2 out of 4 rocker shafts and this was corrected with new plastic inserts and shims. This has resulted in a much quieter top end.

My query is as follows. When removing and replacing the rocker blocks I noticed the top exhaust rocker block engine stud (right cylinder) was very loose, easily turned by fingers. Initially I thought I’d loosened the stud when slackening the nuts on the rocker block so screwed it fully home until it tightened / bottomed out. However, I then realised that the stud was then not long enough to come through the rocker block and allow a nut to be placed on it. I had to back off the stud a number of turns, still easily turned by hand, until exposed thread through the rocker block was the same length as the other 3. Tightened rocker block nuts to specified torque and all appears fine.

Have done a number of miles since, engine definitely quieter, and all appears fine, but the loose stud is nagging me! Is this normal?

Doug

[Kurt in S.A.]

Curious...what torque did you finally use on the nuts? Sure sounded like the engine case threads are stripped, but if it took the required torque, then maybe OK.

Kurt

[Doug-504]

Curious...what torque did you finally use on the nuts? Sure sounded like the engine case threads are stripped, but if it took the required torque, then maybe OK.

Kurt

Torqued to 29 lb ft ( 35-39 Nm). Tightened in stages to final setting. To me it was almost as if the stud was too short, but it did take the final torque setting and as I say, all seems ok?

Doug

[SteveD]

Fingers crossed.
It seems the current widespread practice is to use a torque of 26ftlb as the final step because pulling a stud isn't uncommon.

[JohnT]

I have this problem on my R100R and and fighting shy of carrying out this fix in case it compromises head gasket sealing as only one rocker is affected and would require two head nuts to be slackened.
Did you have any of these problems?

[Rob Frankham]

Exdamine the threads. If they appear complete and the profile is good, refit the stub with stud lock - tighten the nut to the correct torque. If the stud is just a little loose in the thread, it'll be fine. If the thread is so damaged that the thread pulls, it's going to need a thread repair whatever you do now.

Rob

[Doug-504]

Exdamine the threads. If they appear complete and the profile is good, refit the stub with stud lock - tighten the nut to the correct torque. If the stud is just a little loose in the thread, it'll be fine. If the thread is so damaged that the thread pulls, it's going to need a thread repair whatever you do now.

Rob

Thread seemed to be fine when I initially “tightened” the stud until it bottomed out (resulting in it being too short), and again when I discovered the issue and had to return it to its start point. Stud rotated easily by hand but appeared firm in the threads and no sense of stud “pulling” when torqued but I guess time will tell. Reluctant to disturb it again when all seems fine but if I have to remove it in future I’ll check.
I guess then that the studs are by design “short” and can be turned in too far? I’m currently just happy with the much reduced top end noise with the end play issue resolved.

[Doug-504]

I have this problem on my R100R and and fighting shy of carrying out this fix in case it compromises head gasket sealing as only one rocker is affected and would require two head nuts to be slackened.
Did you have any of these problems?

On both cylinders I checked and replaced shims and plastic inserts on both the inlet and exhaust rocker shafts. I slackened off the 4 nuts on the rocker pillars in the recommended diagonal pattern. It takes no time at all but I would think to avoid any chance distortion occurring you would have to loosen all 4 nuts even if only removing one rocker shaft and then follow the gradual tightening by stages to final torque setting on all 4 nuts.

[Kurt in S.A.]

I looked at the fiche and found something that I didn't know before. It appears that with the advent of the 1000cc engines, the studs were two different sizes. Each bike comes with 6 studs that are 275mm long with 2 studs that are 297mm long. I'd guess that the longer studs were where the oil comes out and travels down the stud??? Prior to the '77 models, it looks like all bikes had 8 studs of 275mm in length.

Oak had written that the amount of stud left exposed past the rocker nut is around 1/4"-3/8". Tom Cutter wrote that he installs studs that are from 9-7/8" to 9-15/16" outside of the engine case. Doing some math with Tom's numbers, the distance past the case is about 250mm. That means that around 25 to nearly 50mm of stud is screwed into the case.

Kurt

[Rob Frankham]

I looked at the fiche and found something that I didn't know before. It appears that with the advent of the 1000cc engines, the studs were two different sizes. Each bike comes with 6 studs that are 275mm long with 2 studs that are 297mm long. I'd guess that the longer studs were where the oil comes out and travels down the stud??? Prior to the '77 models, it looks like all bikes had 8 studs of 275mm in length.

Kurt

That's correct.

Looking at the fiches, it seems apparent that this applies to all R80 and R100 engines. For some reason, it doesn't appear to have been applied to R60 engines... although I would want to check to be sure if I were dismantling one.

I don't think it has to do with the oil supply to the rockers. firstly, there are 4 studs tunnels that supply rocker oil (all of the top ones) and only 2 longer studs and secondly, my memory is telling me that the longer studs are the rear studs on one side only which would mean that only one of the oil carrying stud holes has a longer stud.

The accepted explanantion seems to be that it's the rear right studs that are longer and that the holes in the crankcase are smooth sided for the first part of the bore (see https://www.boxerworks.com/forum/viewtopic.php?t=5895). No one seems to know why this was done... just another piece of esoteric BMW lore...

Be aware that inserting a longer stud into one of the other threaded holes may cause the stud to foul the crankshaft which isn't a good idea!

Rob