Help diagnose a squeal in my engine?

#1

I need to diagnose a squeal coming from the engine of my '88 325is, and am interested in hearing your thoughts. I posted a 1 minute video exhibiting the problem.

Video Link: http://www.youtube.com/watch?v=XodmMXbSiwE

[ul]
Info:

  • it only happens when engine is cold.
  • it’s independent of the water pump, alternator, and pwr steering pump (which was removed)/ I removed the v-belt and the squeal remains.
  • a slow cyclical noise, appearing at a slower pace than the cam rotation / I watched cam rotation through the oil filler cap while listening to sound.
  • unknown history of timing belt replacement.
  • I put a stethoscope on and couldn’t locate the noise when poking around.
  • I did notice that my water pump pulley has a small bend in it, but it’s not making contact with the crank pulley or anything else that I can see, and as I mentioned, the sound occurs when the v-belt is off.
  • it seems to be getting worse.[/ul]

I’m guessing it has something to do with the timing belt or timing belt tensioner, but haven’t opened up an M20 engine before, so I’m looking for any thoughts from people who’ve been there.

Thanks in advance!

Bryan

#2

You’ve done everything I would do to diagnose it. I’d have to guess belt tensioner at this point.

#3

That by itself would be enough to make me replace the timing belt and tensioner, whether it is the cause of the noise or not.

#4

you’re absolutely right. The whole timing belt, tensioner and water pump enchilada sounds like the ticket. There looks to be plenty of info online about getting the job done.

thanks for the input.

Bryan

#5

As mentioned, most definitely water pump or tensioner. I had the exact same noise last fall. One new water pump, timing belt, and tensioner later all is quiet again. On my car I suspect the water pump was the culprit. The shaft was wobbly. Usually not a good thing. :lol:

#6

I am doing the job right now and just decided to quit for the night. The last time I did a timing belt and tentioner was on my 88ix. I swear I did not ever have to remove the crank pulley and dampener but it looks like I do. This is probably the 4th time i’ve done the job on the e30. My dad just brought up my bentley manual and was helping me with the job. He was reading it and it says I need to remove it. Anyway I quit with the lower bolt in the lower timing belt cover still in. There’s no way I can get a socket on it without pulling the dampener.

#7

If I remember correctly, You don’t have to remove the dampener, just the pulley. the pulley is bolted to the dampener with 4~6 8~10mm bolts. You have to work on feel, you can’t see them.

It is has been a year since I have done this and this is all from memory so probably not 100% accurate.

#8

You have to remove the harmonic balancer/pulley to change the timing belt. It is held on with six bolts.

#9

ah, I almost forgot to post my results…

Turned out to be the tensioner pulley. After getting the pulley out I gave it a good spin and could hear a faint oscillating squeal. At slow speeds it sounded like the bearings were made with gravel. All the other parts looked fine.

With the help of a nice write up from e30world.com (link) I was able to do the standard front end maintenance with no problems: timing belt, belt tensioner (with new spring and pin), water pump, thermostat and hoses. This stuff wasn’t on my list originally but it definitely should have been, so I figure it’s kind of a good thing it was squealing for my attention.

Thanks for the bits of advice,

Bryan