Hi there, 

While putting everything back in place in the engine (just covers were out), I noticed that one of the valve cover bolts was not tightening at all. I used a torque wrench (9NM) to tighten them. I thought to sort this out a bit later but ..okay.. I could not help it. So, I took the valve cover out and realized one bearing clamp having cracks (see pics). Also saw that there were helicoil type threads attached to a bolt. So, someone had fixed threads in the past. By the way, I did not fired up the engine since last autumn. It has been in a warm garage all the time. 

Another odd thing is that metal structure at the bottom of threads hole looks like the surface of the moon or cheese. It is not like machined. When we look at the bearing surface things turns out to be even more peculiar - pitted surface! I do not feel any scratches with my finger nail but I do feel those pits. Do you have any idea what makes those holes? Corrosion, lack of lubrication, casting quality or something else? Camshaft is visibly in a good condition. I did check other clamps and there are no problem with them. Only this one (n:o is scrap. 

Anyway, I just ordered a replacement (used) from Germany. 

I suspect that the voids you see were cast into the part.  It seems that BMW had/has a problem with porosity in their castings.  The black coating inside the valve cover and the oil sump is there to prevent oil from seeping through the parts.  It's also been said that the finish on the wheels is not just cosmetic, but helps seal against air leaks through the rims.  

Your broken cap is a great warning about always using a torque wrench to tighten the valve cover screws.  It appears that someone in the past over tightened that screw and cracked the boss on the cam bearing cap.

You do know that those caps are matched to the head and aren't just a bolt on for a repair part?  I would use some Plasti-Gage to make sure there is proper clearance between the cam and your replacement bearing cap.  You may have to adjust the fit with shims or removing a little from the faces where they contact the cylinder head.  You don't want the cap pressing down on the camshaft or allowing an overly loose fit.  Maybe someone here will chime in with some advice on how to fit your "new" bearing cap.

You can't just replace that cap, that's likely to leave you a broken camshaft or destroy the head. AFAIK it's line bored. 

But there is a mod done for a repair to overcome this event and I think is sidecar Paul came up with it. I have an idea it is a bridge piece.


I don't even think you need as much as 9NM but to prevent it happening it's a good idea to replace the soft washers so less torque is needed. Old ones get hard. 
 
That bearing cap is well goosed. Any photo of the camshaft bearing surface?

Don't be concerned about the bearing surface I have seen it before and as .75 said it's part of the casting before machining.
To fix it remove the remaining part of the tower and make this out of steel.

It is certainly the case that the heads and caps are line bored and therefore 'matched'. It always surprises me to see heads sold without caps, and vice versa on oohbay....oh well!

However....these are old bikes and some fudging is always worth trying and acceptable if it works. I haven't done this yet because I haven't been on the OP's situation, but I would be happy to try things with a swapped in cap. You'd have to strip the head to do this because it would involve staged assembly/torquing of the caps with just the cam installed - no valve gear. Feeling for resistance/checking for play would tell you if it was going to be okay. There are ways.

That said, I like the look of the 'steel bridge' fix.

Hi,

I felt myself quite a newbie when not remembering that clamps and the head should match. Thanks for a very valuable quidance. 

I made today a steel bridge as Chris846 and some others suggested, according to a pic RicK G posted. Mine is not beautifully constructed, but it is working. I used my "precision" tools like a small angle grinder, a file and so on and put the old clamp back there with assembly lube. I thought it is scrap due to pits on a bearing surface. Anyway, two used clamps (or caps?) are on the way already. According to most of the comments I do understand that they are useless for me. Not a big thing. Learnt again. I should think first and then act. Not vice versa  . 

I would like say that looks a lot nicer than anything that would come off of my workbench! Nice job!

92KK 84WW Olaf wrote:That bearing cap is well goosed. Any photo of the camshaft bearing surface?

I didn't take a picture of it but I did check visually all caps and camshaft necks. The neck of this point looks exactly like the others - no scratches visible. I wondered this after seeing the pits. Could it be just casting issue or something? There were no abnormal noise or something last time the engine run.

Thanks, Point-Seven-five  

JiiPee63 wrote:Hi,

I felt myself quite a newbie when not remembering that clamps and the head should match. Thanks for a very valuable quidance. 

I made today a steel bridge as Chris846 and some others suggested, according to a pic RicK G posted. Mine is not beautifully constructed, but it is working. I used my "precision" tools like a small angle grinder, a file and so on and put the old clamp back there with assembly lube. I thought it is scrap due to pits on a bearing surface. Anyway, two used clamps (or caps?) are on the way already. According to most of the comments I do understand that they are useless for me. Not a big thing. Learnt again. I should think first and then act. Not vice versa  . 

That's it! No camshaft or line boring issues. Not much torque needed on the cam cover bolts, err on the light side.

Point-Seven-five wrote:I suspect that the voids you see were cast into the part.  It seems that BMW had/has a problem with porosity in their castings.  The black coating inside the valve cover and the oil sump is there to prevent oil from seeping through the parts.  It's also been said that the finish on the wheels is not just cosmetic, but helps seal against air leaks through the rims.  

Your broken cap is a great warning about always using a torque wrench to tighten the valve cover screws.  It appears that someone in the past over tightened that screw and cracked the boss on the cam bearing cap.

You do know that those caps are matched to the head and aren't just a bolt on for a repair part?  I would use some Plasti-Gage to make sure there is proper clearance between the cam and your replacement bearing cap.  You may have to adjust the fit with shims or removing a little from the faces where they contact the cylinder head.  You don't want the cap pressing down on the camshaft or allowing an overly loose fit.  Maybe someone here will chime in with some advice on how to fit your "new" bearing cap.

I would get some plastigauge and measure the stock one, then measure the replacement and get it as close as possible with either shims or trimming.  Be sure to do each side the same to keep the new one aligned to the cam.

Thanks  . Just wondering which measuring range I should consider in case of a clamp change? There are packages (5-10 strips) for 0.025-0.175mm, 0.100 - 0.125mm and some packages with greater tolerances.

I would go for the .025-.175mm.  I can't imagine the clearance being large enough to use the larger size.  

I would go a long way toward using the old cap with the bar for holding the valve cover screw before trying to use a replacement.  A replacement will mess with the fit of the cam bearing at that spot, and will always be a weak spot in the mechanical integrity of the engine. Fitting that new cap is a desperation repair.

I would not even consider using anything but the original cap and the repair you did. It is highly unlikely that either of the caps you bought would fit let alone be a good fit and you would most likely end up with a damaged cylinder head that would be a very expensive fix. The repair you did would be stronger than the original cap and the small imperfections are of no concern.

Hi, thanks .  Got used parts this morning. I noticed small cavities at both of them. So, these parts being as a reference, I believe there shouldn't be any problem with the original one.

RicK G wrote:I would not even consider using anything but the original cap and the repair you did. It is highly unlikely that either of the caps you bought would fit let alone be a good fit and you would most likely end up with a damaged cylinder head that would be a very expensive fix. The repair you did would be stronger than the original cap and the small imperfections are of no concern.

Just to add, there are some incidents on the forum of camshafts breaking.

I suspect these arose due to this cap being changed and not realising the consequences of doing this.