Disconcerting engine noises

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UsAndThem

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Hi,

I'm new to bmw’s and the m30 so I was hoping that you all might be able to help me identify the source(s) of some bad engine sounds my Bavaria is making. I apologize ahead that it's not a coupe but I figured that you guys would have some expertise since they share similar engines. The brief video below captures the sounds fairly well.

http://www.youtube.com/watch?v=Ka-gEhOqYNs

There are two distinct sounds (other than typical engine noise) present. The first, and my main concern, is best described as a vibrating/grinding sound. Initially, I checked everything for vibration and/or interference. The sound seems to be originating near the water pump so I went ahead and replaced it but the sound remains the same. The car was purchased two months ago and I have been performing standard tune-up items like spark plugs, oil change (20w50), points, cap and rotor. The dwell is right at 35.5 degrees and the timing is set at 1700 rpm per manual specification.


The second sound is an intermittent squealing/ screeching that I am confident is the alternator because I can hear it when I rotate the alternator by hand.

Any thoughts or comments would be greatly appreciated.

Brian
 
One noise I hear that sounds familiar, I believe is the alt pulley/blades rubbing against its body...you seem to have isolated it by hand. I had one that made this noise just by manually turning the belt. By hand and vice grips I reorientated the blades of the pulley/fan and no more noise. I had probably bent it when swapping one or isolating/locking the fan belt??

The other noise may be a loose timing chain tensioner or chain?? It does not sound like it comes from the core (low end/block). It does seem to come from the upper front of the engine...well from my seat while watching a video...

Good luck,
Jon
 
Uniform rattle or clatter could be valve train (worn rocker bushes, improperly adjusted valves, loose oil sprayer bar?), or as Mr. Shark suggests, the timing chain (and guides and tensioner). The sound/s could just as easily be caused by something loose, worn or broken that is external to the engine. Annoying sound can be a result as a symphony of many loose or worn parts. I wouldn't overlook the seemingly remote possibility that you have one or two exhaust leaks. These can mimic a metallic rattle too.

Do you still have an air conditioner compressor? Alternator, Steering pump and air cond. compressor typically have rubber bushings that can wear or become loose. You mention the alternator as being suspect. All of the rotating accessories have bearings that can dry out or wear. A dry bearing on any of these rotating units can make a horrendous noise. Remove belt tension, inspect and spin is one way to diagnose.

You may have already tried this. If you haven't done so, consider using a length of garden hose or similar. Put it to your ear with the engine running and try to isolate the general source of the noise. For all you know, the noise could be the result of a loose metal exhaust shield or a carb filter adapter plate or even a fuel line hose clamp striking another metal part.

hth
 
You may want to check the fan clutch for play. Also, when I first bought my Bavaria it had a intermitant loud clunking that as it turns out was caused by worn rubber bushings in the alternator mount, causing it to wobble slightly but make alot of noise.
 
Thanks for all the suggestions. I made a poor man's mechanic stethoscope this afternoon and did some listening to different locations. It seems that the alternator is probably the culprit for both noises. I listened to different parts of the valve cover and heard some slight ticking noises but nothing that would be causing the more significant noises. I also listened to the chain tensioner and what I heard sounded like it was running smoothly. The A/C compressor, belt and bracket have all be removed for the time being so they obviously weren't the source. I am going to check the fan clutch and do some more listening. I will report back on the alternator when I get it out and take a look at it. Thanks again for the quick responses and good suggestions.

Brian
 
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