diagnosis? M60 Knocking (jam packed with info)

[31Hertz]

Okay, I am hearing a strange noise from my car. It is a non-rhythmic knock type sound. It does seem to increase in frequency as I rev the engine, but does not seem to be proportional to engine revs. I cannot hear the sound when I open the hood. The sound is more pronounced when I am on the ground at either side of the car behind the front wheels, but not from under the front air dam. The sound does not go away when I press in the clutch. I have no driveability issues whatsoever. The engine revs freely and does not miss a beat on acceleration. The clutch/shifting seems just as smooth as ever. The sound does not seem to decrease as the engine warms. I have replaced both cats (DEC mfg) a few months ago, but am not ruling them out as a possibility. But the cats do not rattle when I strike them with a wrench. It is a lower toned sound than the "marbles" cat sound. Could this be the throwout bearing? Please say it ain't a main bearing or a conrod:( ... Please give me your advice. I have tried to supply all information I can think of. The clutch was changed out along with the flywheel at 90K miles. Hopefully I have included enough information as it may be a while before I can respond to any further questions you may have for me, but will do so by 08/31/06 1:45 PM ET USA. Thank you in advance for any direction you may be able to provide.

[bbig119]

That's funny, I started noticing a similar sound with nearly identical conditions to those you just described. I didn't post yet because I haven't had a chance to look into it as much as you have.

I began noticing distinctly when I start the car to head home from work. I can still pick out the sound when I pack at home, but its not as distinct as when I start it up-- maybe because I've adjusted louder wind/engine/road noise on my drive home. This sound appears to also vary with rpm in terms of the frequency of knocking, but it doesn't get louder. As with 31Hertz, the car also drives fine. Initially I thought it may just be valve tap as both a mechanic who did the pre purchase inspection and a friend of mine who's got two e28s picked up and mentioned that.

AFAIK the clutch hasn't bene changed since the PO swapped in a manual 6spd about 90k-100k ago.

Sorry I can't help more, but I'm interested in any ideas you guys have.

[632 Regal]

engine and trans mounts?

[31Hertz]

engine and trans mounts?

Engine mounts do need to be replaced. Transmission mounts are good. If the engine mounts are the problem, how is the sound being produced OR is it the mounts themselves making the noise? It sounds diesel-like, but without a genuine rhythmic quality.

[bbig119]

I seem to remember engine mounts being ok, don't know about the trans mounts.

[632 Regal]

the engine could be moving around from the bad mounts, occasionally producing that sound especially if its not rpm related.


Engine mounts do need to be replaced. Transmission mounts are good. If the engine mounts are the problem, how is the sound being produced OR is it the mounts themselves making the noise? It sounds diesel-like, but without a genuine rhythmic quality.

[31Hertz]

ok, thanks Regal. It may be a while till I can get to the mounts, as the heater core is next on the list. Not looking forward to it, but will be glad when it is done. Do you think damage of any kind is occuring? Should I fast track the engine mount project?

[bbig119]

ok, thanks Regal. It may be a while till I can get to the mounts, as the heater core is next on the list. Not looking forward to it, but will be glad when it is done. Do you think damage of any kind is occuring? Should I fast track the engine mount project?

Good luck with the heater core, I did it three weeks ago and didn't enjoy it at all. If I can be of any help, please let me know.

[BrianH]

Hi Hertz,
This is a shot in the dark, but could it possibly be a rattling dual-mass flywheel? As they get old, they tend to rattle a bit, especially when you shut off the engine. If you have the car sitting still and making the noise, and then let out the clutch in first gear slowly, does the sound quit when the clutch engages? As I said, just a guess, but it's something to consider.

[BillionPa]

........... i dunno why nobody has mentioned this yet, but it could be a bolt flipping around the oil pan or something? or massive slack on the oil pump chain, mine sounded suspiciously similar to this.

[winfred]

one unusual noise a m60/62 can make that's a bitch to find is when one of the headers comes apart internally, they are a double wall construction and the inner wall can break loose and knock randomally, this happened to the managers e38 and was some fun to find

[31Hertz]

I do not believe that it is the flywheel. I know that rattle from very conservative gassing while clutching first gear. I Loctited the oil pump mounting bolts, tightened the oil pump body bolts, and took the slack out of the chain earlier this year; so I would hope they have not backed out again this soon. My intuition tells me that the bad engine mounts are not causing the noise either because the block is very stable at idle (although they really do need to be replaced). The more I think about it: the more I think it might possibly be the cats failing again... The noise is similar; if I can recall a sound from four months ago. The first time it happened (stock/original cats) it sounded like the transmission was throwing something around inside the housing. But when I struck the cats with an adjustable wrench, there was a horrible rattle / clatter (much to my relief). But this time there is no noise when I strike the cat. I am gonna go hit those fukkers again at lunchtime. I have read on some other forum about an E39 540 that had a problem with new DEC cats rattling shortly after installation, but the shop I took her to swore by the DEC cats over Magnaflow. It may be time to take it back to the shop that did the install to get an appraisal of the situation. I will keep you all informed as soon as I am able to get the car to the shop. Meanwhile, your further input is greatly appreciated!

[31Hertz]

reviving old post to say that I found the source of this noise: The pivot bolt for the A/C belt tensioner had snapped in two. This caused the A/C drive belt to flop around. The belt was intermittently being grazed by the radiator cooling fan... Now I just need to get at the bolt. Tight squeeze in there:(

[BillionPa]

i have a tensioner assembley if you want it (if you havent getten one already)