Idler pulley squealing... again!

[bison]

Hi -

A couple of months ago I replaced all the idler pulley and both tensioners (as well as water pump, t-stat, and belts) on my 2000 E39 with M52 engine. In the last week or so I've noticed that the squealing is back and I think it's from the top idler pulley (the one that just deflects the main belt downward). Ugh. A couple of questions about this:

1) I released the tension and slipped the belt off the alternator, then checked the pulley. It turned OK without any grating, could it still be making noise?

2) Is it possible to briefly run the engine after releasing the tension to verify that it's one of the pulleys? It doesn't look like the belt could get caught on anything, but I certainly don't want to do something dumb.

3) Can I replace the deflector pulley without removing anything else? It looks like I can.

4) Is there supposed to be a dust cover on this pulley? There isn't now, so I can see the head of the bolt that holds it in place. I don't recall if the prior pulley had a dust cover, if so I tossed it. Could a missing dust cap make it fail in four months of easy driving?

5) Why on earth could this have failed so quickly? I got all parts thru Bavarian Autosport.

Thanks!

[ahlem]

Maybe ask Otto, the technical line at Bavauto.
I think the number is 1800-535-2002

[Tiger]

Squealing is usually the belt noise... maybe some coolant or oil contaminated the belt. Wash that belt with dishwashing detergent and see if the noise go away.

Sometime the aftermarket tensioner really suck in quality... I bought a cheap one and you usually just have to tension it all the way and it will auto tension the whole thing... but this one doesn't and causes binding that my alternator squeals immediately... my alternator bearings are iffy to begin with... original.

You can tell if the pulley bearing is shot... spin it... if you can feel slightly rattling feeling... it is bad... no doubt. New pulley are harder to spin and smooth... no bumpity bumpity feeling or vibration.

[genphreak]

Beware also, there are two ways to thread the serpentine belt. If you use a shorter one (as the PO had managed to install a 1500mm one on my car) it will thread incorrectly and squeal and cause problems for LAD and steering assistance under load. Make sure yours is the proper length belt (1570?) and if the squealing is not caused by belt wear/contamination, inspect the idler pulleys and the tensioner and its pulley; I've seen intermittent noise caused by the bearing in the tensioner pulley on a non-LAD equipped M50B25 before.

[Rick L]

As Tiger mentioned... Most likely it is the belt. Belt squeal and pulley rattle when bad. Dust cap will prolong the life of the pulley by keeping the dust/dirt out.

[bison]

Fixed it - the idler pulley was indeed bad despite being replaced recently. Partially my bad for having bought the $20 JL aftermarket one rather than the $50 OEM part, but still annoying. Bavauto is going to refund the cost of the bad part. It is possible to replace the pulley without removing the fan, I just removed the air intake box to give me more access.

[Rick L]

INA is OE manufacture of BMW pulleys and cost 1/2 the price of BMW branded INA pulleys. You should be able to change the pulley without taking the fan out.

[632 Regal]

Beware also, there are two ways to thread the serpentine belt. If you use a shorter one (as the PO had managed to install a 1500mm one on my car) it will thread incorrectly and squeal and cause problems for LAD and steering assistance under load. Make sure yours is the proper length belt (1570?) and if the squealing is not caused by belt Now this is interesting. I lose my power steering on corners ever since I replaced the belt many years/miles ago. Must get a belt routing diagram and check it.