Who (or what) is tapping under my intake manifold?

[bsell]

In this thread http://www.bimmer.info/forum/showthread.php?t=36900 I asked about re-using my new valvecover gasket to chase a noise.

Well, I got around to popping the cover off to see what might be causing the tapping noise coming from the #5 or #6 cylinder area at what sounds like either the injector or cam followers for those cylinders. It is not a rod big end or wrist pin knock as the noise is not load dependent, just engine speed dependent. If I had to describe the sound, it almost sounds like something metal bonking plastic yet there is no tapping sensation in the intake manifold nor does the noise sound louder through the oil fill hole in the valve cover.

The sad thing is, this noise was not there before changing out the gasket two weeks ago. Nothing fell in the cam area and I just looked under the intake cam splash guard (and through out the upper area of the head) and everything looks kosher. All of the head bolts are doing their job and all nuts and bolts are accounted for. I disturbed the least amount of stuff in taking the valve cover off and I still ended up with a new (coincidental?) noise.

I put a bottle of engine detergent in the oil last week in the hopes of cleaning any junk out of the offending follower if that was the problem. Things are cleaner in there but it wasn't that bad to start with and the noise is exactly the same.

So what lives under the intake that might be knocking to get out?

If there is nothing living in there that could cause this noise, I figure I better take an oil pressure reading at the back of the head (if possible) to see if I have **** for oil pressure in a car with 120K kilos and good looking cam lobes and whatnot.


What say you all?
Brian

[Jon K]

Check your 2ndary timing chain tensioner - it could just have started to get weak by chance.

[ahlem]

Did you check the valve clearances while you were under there? Maybe an adjustment is needed. Also, some models of BMW tend to have their exhaust studs loosen and you get a progressively worsening ticking as you get more looser.

[bsell]

Check your 2ndary timing chain tensioner - it could just have started to get weak by chance.

You mean the one that connects the two cams? I did give her a squeeze while the cover was off. This thing has had the 'vanos growl' ever since I picked her up off the boat (after shipping from Japan). But she always has run strong in the upper revs so I haven't done anything about it. The local (German) mechanics talk like changing parts doesn't always fix it (shrug their shoulders like it ain't no big thing it's noisy).

So now I made a bad situation worse by squeezing the tensioner. Way to go Brian! I take it the loose chain allows the cam to 'slap' around causing the noise. The old Subaru flat fours in the Loyals would 'slap' the distributors around when the cam belt was old and loose. I could buy your diagnosis.

The chains looked mint by the way.

Thanks for lending me your brain cells,

Brian

[bsell]

Did you check the valve clearances while you were under there? Maybe an adjustment is needed. Also, some models of BMW tend to have their exhaust studs loosen and you get a progressively worsening ticking as you get more looser.

This valvetrain (M50, single vanos) has the cam lobes operating the hydraulic followers directly, without rocker arms. I do have some concerns about dislodged gunk blocking an oil passage in the hydraulic follower but there isn't much I can do other than strip the valve train out and give her a thorough cleaning...

I've chased what you described in an old '73 Capri (2.6L) and a '78 Mustang (don't ask!) 2.8L V-6. Luckily the studs didn't back out but the adjusting nuts were another thing. Those things liked to go back to the original setting no matter how hard you tightened the adjusters. It was better to buy new adjusting nuts than to reuse the old pieces.

You know, that Capri used to roll the tires over from a dead start even through the slush box. That was one fun (and safe) car to learn to drive in. Plus the three of us boys ragged the hell out of it and she took it all in stride.

Thanks,

Brian

[bsell]

Noise is a real pain to identify let alone locate so you have my sympathy for what its worth. If you only took off the valve cover, is it possibleyou put two washers under one cap and left one short? The cap would tighten down but wouldnt grip the cover and you might get a rattle at that point? Spent a few minutes wondering where a washer had disappeared to once

I replaced the rubber doughnuts on all of the cover nuts and made sure each set only had one washer the first go round. I have since R&R'd the cover and the only problem I had was the ground wire for the coils was stuck to the cover nut. That's what I get for over-tightening it!

Thanks,

Brian

[whiskychaser]

Noise is a real pain to identify let alone locate so you have my sympathy for what its worth. If you only took off the valve cover, is it possibleyou put two washers under one cap and left one short? The cap would tighten down but wouldnt grip the cover and you might get a rattle at that point? Spent a few minutes wondering where a washer had disappeared to once

[bsell]

Thanks to all that replied. I am posting the 'fix' in this post so others may know what the deal was when they search.

I found spark plug #6 loose while changing the spark plug leads yesterday. After pulling all of the plugs to ensure they are still clean, I tightened them all down. (Yes, I checked them all twice this time! ) I swear I had tightened the plugs down after looking at them during the valve cover gasket job but I guess 'old-manitis' set in and I left one loose.

Anyway, I am happy to have solved my self-induced noise.

Thanks to those that contributed help,

Brian