ID this noise?

[BimwadM42]

Hey all,

I'm trying to determine the source of a noise on an early E36 M42 with about 110k miles on it.

It sounds like a high-frequency buzz, with a hard, metallic edge to it, audible both inside and out.  Think of a mosquito in your ear, except with a lower pitch, or an electric razor with a higher pitch.

It occurs only at ~3000k rpm, not at other engine speeds, and doesn't vary with rpm.  As long as the engine is kept at that narrow rpm range, it will emit that sound.  It will briefly emit the sound as it passes through the "sweet spot" when revved up or down.

It seems to occur only after the engine has warmed up.  Load or no load.

It used to be an occasional thing, but is occurring more frequently of late.

At first, I thought it might be a loose heat shield or the cat, but they have both checked out.

Checking with the hood open, it now appears to be emanating from somewhere under the valve cover in the middle of the engine, but that's just a general impression.  Though these things make all sorts of noises, this one is quite distinct, and a bit ear-piercing up close.

I've looked through many of the threads here on the tensioner, lifters and guide rails but I don't know if they apply.

The fact the it occurs only at a particular engine speed leads me to believe that something loose or worn is hitting a resonant frequency.

The tensioner was replaced at 65k with the new style along with the profile gasket, so it has about 45k on it.  I know what kind of racket a bad tensioner will cause on a cold start, but that isn't the case now.

Engine otherwise runs normally, and though it does burn oil, it doesn't leak a drop.

Any clues?

[roundel318]

Would it be easy for you to rule out belts quickly?
That would get them off the checklist and us onto things inside the engine......
Your tensioner has pretty low miles to be going bad, but it is possible I suppose?

[BimwadM42]

Yep, I can rule out the belts.  It's a mechanical, hard metal-to-metal sound.  I'll try to get a sound sample.

I'm gonna try to narrow down whether it's an internal or external source, but these motors are so noisy in general, it makes it difficult.

The fact that it occurs only within a narrow range of conditions, and doesn't vary in intensity or with engine speed, has me stumped.

I'll prod all the external parts that are connected to the head, like the exhaust manifold and ignition wire channel, to eliminate the obvious.

[roundel318]

Interesting, with belts out, can you get a recording of it?
I would suggest swapping the tensioner if you had a spare......
Just to check it off the list?

[peerless]

Well, your probably not going to want to hear this, but....

When BMW built these engines, they for whatever insane reason decided to only use half a thrust bearing shell. So you only have 180* of axial load support for the crankshaft.

All other BMW engines and just about every manufacture that I have seen have 2 thrust bearing shells giving a full 360* of load support.

Why BMW chose to install only half a shell is beyond me, especially considering the M42 is a buzzy, hi revver to begin with.

I don't know for a fact this is your problem but you seemed to have ruled out everything else. You can use a mechanics stethoscope to check the noise out in better detail.  Check at the lower crankcase and/or oil pan, rev to the 'sweet spot' and listen.

[doitover]

And yet they routinely go over 160,000 miles, what pieces of crap.

[batsbats]

I have also an odd vibration that is felt throughout the drivetrain @ ~2k RPMs.

So much vibration, the shifter begins to shake moderately in range, but definitely shaking.  Occurs in or out of gear.

I think we both have one of the described problems Peerless mentioned.

[batsbats]

I have also an odd vibration that is felt throughout the drivetrain @ ~2k RPMs.

So much vibration, the shifter begins to shake moderately in range, but definitely shaking.  Occurs in or out of gear.

I think we both have one of the described problems Peerless mentioned.

[peerless]

And yet they routinely go over 160,000 miles, what pieces of crap.

Hey, I know you guys like your M42s and of course your going to defend them. And thats commendable. But the reality is they are self destructive and extremely expensive to repair.

[BimwadM42]

Well, interesting, if not exactly comforting info to digest.

Wouldn't all these faults in the chain drive and internals manifest themselves somewhat noticeably, and at more than one engine speed?

I haven't really had time to dive deeply into this, but I'll probably have a friend with a stethoscope assist once the holidays are over.

I did discover that oil is seeping into the #2 spark plug chamber, so I guess it's time to renew the gaskets again, which would also allow me to check out the valvetrain.

Aside from the profile gasket, the engine has been solid in my experience.  I know of an E30 version that was also trouble-free for close to 200k living mostly on Mobil 1 like mine.

I'm not in absolute love with the M42, but I can think of more than a handful of faults, external and internal, that strike the M5x engines more often.

[roundel318]

With only 110k on the clock, you wouldn't think his motor would be in such bad shape, at the same time, anything is possible with poor care.
How long have you owned this car?
Do you have any maint. records?

[BimwadM42]

I've owned it since new.  It was broken in on Castrol GTX, then run on Mobil 1 15W-50 at roughly 3-6k intervals, depending on whether there was track time involved.  For the last few years, it has been driven a lot less, so those mileage intervals took a lot longer to achieve.

It's due for another change imminently, so I'll at least be able to determine whether fresh oil has any effect.

I threw together a page with some videos on it.  It doesn't have any fancy formatting, but any reasonable browser should be able to view the videos.  They're from a still camera, so they're in motion JPEG format inside an AVI container, roughly 30 secs and 3MB.

The camera's mic didn't pick up the intensity of the buzz well, but it gives you an idea of what it sounds like and how it comes and goes with rev changes.

http://bimmerfix.googlepages.com/m42buzz

[roundel318]

I've owned it since new.  It was broken in on Castrol GTX, then run on Mobil 1 15W-50 at roughly 3-6k intervals, depending on whether there was track time involved.  For the last few years, it has been driven a lot less, so those mileage intervals took a lot longer to achieve.

It's due for another change imminently, so I'll at least be able to determine whether fresh oil has any effect.

I threw together a page with some videos on it.  It doesn't have any fancy formatting, but any reasonable browser should be able to view the videos.  They're from a still camera, so they're in motion JPEG format inside an AVI container, roughly 30 secs and 3MB.

The camera's mic didn't pick up the intensity of the buzz well, but it gives you an idea of what it sounds like and how it comes and goes with rev changes.

http://bimmerfix.googlepages.com/m42buzz

Fresh oil always makes my engine run just a bit smoother.
How many miles was your original profile gasket replaced at?

[peerless]

I just watched all your videos and heard the noise your talking about. That sounds like a piece of tin steel vibration.

Check the sheet metal heat shield for the spark plugs, when the engine is making that noise start pressing on things like the plastic cover for the plugs and the sheet metal shield for the plugs  until you can make it go away etc..

That doesn't sound internal at all. That motor sounds fine and typical of a M42.

I've owned it since new.  It was broken in on Castrol GTX, then run on Mobil 1 15W-50 at roughly 3-6k intervals, depending on whether there was track time involved.  For the last few years, it has been driven a lot less, so those mileage intervals took a lot longer to achieve.

It's due for another change imminently, so I'll at least be able to determine whether fresh oil has any effect.

I threw together a page with some videos on it.  It doesn't have any fancy formatting, but any reasonable browser should be able to view the videos.  They're from a still camera, so they're in motion JPEG format inside an AVI container, roughly 30 secs and 3MB.

The camera's mic didn't pick up the intensity of the buzz well, but it gives you an idea of what it sounds like and how it comes and goes with rev changes.

http://bimmerfix.googlepages.com/m42buzz

[B318M42W]

just wondering... does it always do that sound when you get to the "sweet spot" or is it just a "phase"