Rocker Arm/Shaft Question - Alignment

[Ian_UK1]

Having just removed the cam cover from my engine with the intention of adjusting the valve clearances, I've noticed that all the inlet rockers are misaligned with the tops of the inlet valves.

The amount of misalignment is about the same for every valve - approx. 1/4" towards the back of the engine - and is sufficient that I'm quite concerned that the eccentrics at the end of the rockers could be close to falling off the side of the valve heads in operation.

My first question is simply "does anyone know what might cause the whole inlet rocker shaft to have moved backwards in the engine by about 1/4 inch"?

The second one is obviously "is there any way to correct the problem without having to remove the cylinder head"?

Car is a UK 1985 635CSi

Thanks in advance to anyone who can help me with this one.

Ian

[Ian_UK1]

I've just found another thread on here from several years ago - the OP had exactly the same issue as me and posted some excellent pics to illustrate the problem. Thread here:

viewtopic.php?t=3596&highlight=rocker+shaft

Unfortunately, there was never a resolution on the previous thread, so I'm still in the dark as to what to do.

[Brucey]

well the rockers are located on the rocker shaft using snap rings, springs, thrust washers and spacers.

http://2009.bmwfans.info/parts/catalog/ ... rm_valves/

There are only three ways of going wrong here;

1) wrong rocker

2) wrong spacers

3) wrong rocker shafts

Now, there is only one rocker type, the spacers are difficult to get wrong (but go on, surprise me) and there are four different rocket shafts.

So my money is on the rocker shafts being assembled wrongly.

cheers

[Ian_UK1]

well the rockers are located on the rocker shaft using snap rings, springs, thrust washers and spacers.

http://2009.bmwfans.info/parts/catalog/ ... rm_valves/

There are only three ways of going wrong here;

1) wrong rocker

2) wrong spacers

3) wrong rocker shafts

Now, there is only one rocker type, the spacers are difficult to get wrong (but go on, surprise me) and there are four different rocket shafts.

So my money is on the rocker shafts being assembled wrongly.

cheers

Now I've got the head off the car, it appears the issue's actually option 4) wrong cylinder head bolts!

The rockers/shafts etc. were correctly installed, but the intake shafts had moved backwards in the head by nearly half an inch, taking the rockers almost off the edge of the valve stems.

The reason the shafts could move so far in the head is that the wide part of the installed head bolts is way too short to reach down as far as the cut-outs in the shafts. Without any positive location, the shafts just gradually moved backwards under the pressure from the springs.

If I hadn't found the problem when I did, the intake shafts would have kept right on moving until they hit the plate bolted-on to the back of the head - by which time the rockers would have missed the valves completely and I'd have one properly knackered engine!

Once I'd removed that plate on the back of the head, a couple of sharp taps with a drift on the back end of the inlet rocker shaft had everything lined-up again in no time. Interestingly, the exhaust shafts hadn't moved because the springs on them push the shafts forward and there seems to be a limit to how far forward the shafts can go.

I'm now going to get new head bolts from BMW - hopefully they'll have the correct-length wide bit to locate the shafts properly. I'm also tempted to make a couple of spacers to sit between the back end of the shafts and that retaining (oil-return?) plate on the back-end of the head. They'd prevent the shafts from moving backwards in the head, even if the head bolts don't locate them properly.

[Brucey]

ah, I see....

I think you are lucky that you didn't get oil starvation. Best be sure that the oil still flows out where it should do when you are done; if the rocker shafts move then you can end up with no oil in the spray bar and that kills the cam.

BTW I'm not sure that spacers in the back of the rocker shafts will be an entirely brilliant solution; if the shafts move they may just push the plate off the back of the head, or cause it to leak, anyway.

cheers

[Ian_UK1]

ah, I see....

I think you are lucky that you didn't get oil starvation. Best be sure that the oil still flows out where it should do when you are done; if the rocker shafts move then you can end up with no oil in the spray bar and that kills the cam.

BTW I'm not sure that spacers in the back of the rocker shafts will be an entirely brilliant solution; if the shafts move they may just push the plate off the back of the head, or cause it to leak, anyway.

cheers

Thanks for the reply. You're absolutely right about the oil situation - the rear oil inlet was almost completely covered due to the movement in the shaft. Both are now centralised where they belong.

I'm unsure about the spacer idea too. However my thinking is - if (big if) the only force pushing the shafts back is due to the locating springs pushing on the rockers - with the engine's natural vibrations facilitating the movement a tiny bit at a time - then the total force is only small and the 6 x M6 bolts holding the oil return plate should cope admirably. If not, then it's potentially leaks and a bent plate as you suggest.

[Brucey]

well normally those forces are taken by the head bolts bearing against the notches in the rocker shafts.

I guess someone fitted the wrong head bolts in your engine... But if you have the right head bolts, any spacers you might put in won't get a look in, will they?

BTW the rocker shafts are probably a pretty loose fit in their bores when the head is hot; the CTE of aluminium is a fair bit less than steel; I think they will probably move if they can; at the least the shafts will probably 'walk' with each thermal cycle.

cheers

[Ian_UK1]

well normally those forces are taken by the head bolts bearing against the notches in the rocker shafts.

I guess someone fitted the wrong head bolts in your engine... But if you have the right head bolts, any spacers you might put in won't get a look in, will they?

BTW the rocker shafts are probably a pretty loose fit in their bores when the head is hot; the CTE of aluminium is a fair bit less than steel; I think they will probably move if they can; at the least the shafts will probably 'walk' with each thermal cycle.

cheers

Yes, by my understanding the rate of expansion of alumin(i)um is about twice that of steel. It would certainly explain how the shafts were able to move under very little longitudinal force.

With luck, the new head bolts will locate everything properly as you suggest. I just hope BMW hasn't stopped making (or being able to source) the 'correct' ones for the M30 of this age. As I'm quickly discovering, what's actually supplied for these cars now is often the 'nearest fit', readily-available alternative rather than the exact, original part .

[Ian_UK1]

Big update on this issue for you.

I've now partially stripped my car's cylinder head and I've found what appears to be a serious flaw in the design of the head bolts that BMW is now supplying for the M30 engine.

The first pic below this is one of the bolts removed from my engine. It's identical to the new bolts (part number 11 12 0 621 144) that BMW now supplies.



The second pic is a view down the inlet rocker shaft drilling of my cylinder head, with this bolt installed in the rearmost bolt hole with the big washer. As you can see, the wide part of the bolt that is meant to engage in the groove in the rocker shaft isn't long enough to even reach the rocker shaft drilling.



This means the rocker shaft isn't located AT ALL by the cylinder head bolts and is free to move fore/aft in the engine.

The next pic is BMW's parts drawing that very clearly show the head bolts (item 11) should have a much longer 'wide shoulder' beneath the bolt head to allow the wide part of the bolt to connect with the groove in the rocker shaft



I can only conclude from this, that the head bolts BMW now supply are very different to the original bolts for this engine. The bolts might secure the head properly, but they certainly no longer in any way properly secure the rocker shafts.

What I've therefore done is commission a local engineers to manufacture some revised head bolts with a 1 inch longer 'wide shoulder' under the bolt head than the BMW bolt has. This will be long enough to correctly engage the recess in the rocker shafts and secure them correctly in the cylinder head. All the other dimensions of the revised bolts will be the same as the BMW bolt. They are being machined from 10.9 tensile-strength hex bar with cold-rolled threads.

It's my intention to make the revised bolts available to others on here. I'll post a further update with pics once I've got the sample bolts back from the engineers.

Ian

[Ian_UK1]

Apologies - the pics appear to have gone missing from my previous post - here they are in order

[Drew]

hello

I do lurk every now and again and covet your cars!! (as I now have a family sensible Alpina B10)



the piccie at the top of this thread is from my 1981 635csi (long sold). I got around the issue by inserting a spacer (a nut) as the OP did propose, however this only works on one set of rockers. The solution worked, and I confess I had not considered the potential downside. But I reckon the lateral forces involved here are low. I too found that the headbolts did not locate the rocker shafts.

IIRC I once found a M30 head in a breaker with exactly the same "mod", which may be where I got the idea from....

[jacko]

Another thing to be conscious of is that rockers are often designed to contact the valve slightly offcenter. This is sometimes done to encourage the valve to rotate slightly to keep the seat surface clean and wear normal.

[Brucey]

stupid question; would it not be as easy/easier to manufacture some tubes that slip over the head bolts and thus locate the rocker shafts?

The reason I say this is that

a) making bolts is expensive

b) making proper stretch bolts is really expensive.

IIRC these head bolts should be stretch bolts.

Hey Drew, how is it going? Got an itch for another 6er yet...?

cheers

[Drew]

Hi Brucey, yes I always have an itch for another 6er, and it is a sad fact that it's an itch that I can't scratch for the time being.

I reckon I'll get an E9 next time round though, not a CSL, probs a 3.0CSi.

Currently knocking about about a mk2 golf gti and a B10 V8S touring that Kevin got me interested in.

apologies for topic wandering, though I reckon Brucey's idea re sleeves for the bolts might work well. You'd only need one sleeve for each rocker bar I think. and you could trial fit with the head off the block.

[Ian_UK1]

stupid question; would it not be as easy/easier to manufacture some tubes that slip over the head bolts and thus locate the rocker shafts?

The reason I say this is that

a) making bolts is expensive

b) making proper stretch bolts is really expensive.

IIRC these head bolts should be stretch bolts.

Hey Drew, how is it going? Got an itch for another 6er yet...?

cheers

Hi Brucey - thanks for a thought-provoking reply as usual. Your idea of making some tubes really intrigued me - it would definitely make sense if you could just drop-in some tubes with the same O/D as the shoulder of the bolt. Should be (relatively, very) cheap and effective. But.....

After reading your idea, I took a micrometer to a new BMW head bolt to see if I could do exactly as you suggested. However, the threads on the bolt are significantly wider than the main shaft of the bolt so a tube of the right size simply won't go on. If I was to make a tube that would go over the threads, it would be loose on the bolt and the O/D would be too big unless the tube was incredibly thin-walled (and potentially not strong enough to locate the rocker shafts). Real shame as your idea is fundamentally very sound.

One thing I didn't mention earlier about using custom 'long-shouldered' bolts was their potential effect on the oil flow in the head. Most of the head's oil flow enters and leaves the rocker shafts at the cut-outs in the shafts (the same ones the head bolts should locate in). This got me thinking that whilst long-shouldered bolts will locate the shafts well, they may also interfere with the oil flow into and out of the shafts (unlike the standard, BMW short-shouldered bolts where there's lots of clearance between the thinner shaft of the bolt and the rocker shaft oil inlet/outlets).

However, if you look carefully at how the oil flows through the head, there are 4 of the 14 head-bolts that have nothing to do with the oil ways whatsoever. This is the same 4 that go through the brackets that support the camshaft oil pipe and they're roughly in the centre of each rocker shaft.

I'm therefore only going to use the long-shouldered, custom bolts in these 4 holes and the inexpensive, standard bolts in the other 10. This will ensure all 4 rocker shafts are properly located near their centre points, leave maximum clearance for the oil flow elsewhere and keep the cost down as only 4 custom bolts are required per installation. Looks like a win, win for now.

Ian

[Ian_UK1]

hello

I do lurk every now and again and covet your cars!! (as I now have a family sensible Alpina B10)



the piccie at the top of this thread is from my 1981 635csi (long sold). I got around the issue by inserting a spacer (a nut) as the OP did propose, however this only works on one set of rockers. The solution worked, and I confess I had not considered the potential downside. But I reckon the lateral forces involved here are low. I too found that the headbolts did not locate the rocker shafts.

IIRC I once found a M30 head in a breaker with exactly the same "mod", which may be where I got the idea from....

Thanks for the reply - very interesting indeed. So the 'nut behind the oil plate' mod does work!

I think I might use this as a belt-and-braces solution together with the custom bolts I'm having made. If the bolts work correctly, the nut will effectively be redundant and will just remain loose behind the plate; if the bolts still allow too much movement in the shafts, then the nut will stop it going too far.

Ian

[Ian_UK1]

Hi everyone - back with an update.

My redesigned head bolts finally came back from the manufacturers a few weeks ago and are now installed in my car's engine. (Please see pics below). The rocker shafts now can't go anywhere (the longer shoulder on the bolts locates them very positively with just enough room for expansion). I've also included a couple of other pics of other parts I've overhauled when they were ready to be re-installed.

Interestingly, when I removed and stripped-down the head, it was obvious that it had been completely rebuilt in the fairly recent past. There was no discernable wear on either the rocker shafts or the rocker bearings themselves and the valves and guides looked almost brand new. Shame the previous rebuilder had neglected to clean anything on re-assembly! At least it meant the rebuild costs this time were relatively low - the only major part needing replacement being the intake rocker shafts that I'd damaged as I removed them!

Whilst the engine was apart, I took the trouble to replace several knackered hoses, all the gaskets and seals and to repaint the rocker cover, inlet manifold and all the air cleaner parts. All the wiring was tested for continuity and all the Motronic sensors checked for resistance etc. This site is an amazing resource for so much of this info! I also had the alternator rebuilt with new bearings, diodes etc.

Not knowing what condition they might be in, I also took the injectors for an ultrasonic clean and was VERY glad I did as they were in a real mess - spraying to the side, different flow rates etc. As you'd expect from 30-yr-old injectors I suppose. The good news was they cleaned-up superbly. They all now have the correct spray pattern and are within well-under 1% of each other for flow at 3 bar test pressure.

My engine's now fully back together and running so much better than before. It now sounds like an M30 should and I'm sure it has all its power and torque back. The valve train, in particular, is uncannily quiet (with 9-thou gaps at the cam lobes). At idle, the injectors clicking are far louder than any residual tappet chatter.

Looking forward to getting the car back on the road now.