Bad idler pulley?

[BMWTurboDzl]

59k miles, BMW N55.

I occasionally hear pulley making noise. It's a faint flapping noise (think Wheel of Fortune, or any Wheel you'd find at a casino). The speed of the sound corresponds with the speed of the engine.

I've narrowed the sound down to the vicinity of the alternator and the idler pulley below it. I have an order ready to go on some torx bits and a torque wrench to replace the pulley, belt, and tensioner but I'm wondering if the sound could be something inside the alternator.

The belt and pulleys are over 6 yrs old so I guess replacing them is a no brained.

Any thoughts or suggestions?

 

[mk378]

Take the belt off and spin each part by hand.

 

[TCL]

Sounds like the belt separating. You'll find out when you take them off to check the different pulleys.
I had one that sounded like a bad tap in the motor and it was the belt.

 

[Supersonic]

Yes, could be something inside the alternator, get a stethoscope or screw driver and listen while touching on the alternator opposite end of the pulley where there's no chance of high danger, there's probably always a risk. This was how I diagnosed it on 2005 Camry, used OEM alternator off eBay was my solution, than old alternator gets bearings re-greased and gets put in trunk for spare in the hopes it would be good enough at minimum in a break down.

 

[drtyler]

The miles are about right for replacement. Is the belt riding in the center of the tensioner pulley?

Go ahead and replace the tensioner, idler pulley, and belt at the same time and you'll be covered for another 60k miles.

I don't have experience with the N55, but on multiple N52 cars this has been the case. Sometimes they make the clicking/tapping noise, a high pitched noise in tune with the revolutions, or I've seen others where the belt starts to ride off the tensioner pulley. I'm sure there are other modes of failure for these parts, but I've not experienced those yet!

 

[BMWTurboDzl]

The miles are about right for replacement. Is the belt riding in the center of the tensioner pulley?

Go ahead and replace the tensioner, idler pulley, and belt at the same time and you'll be covered for another 60k miles.

I don't have experience with the N55, but on multiple N52 cars this has been the case. Sometimes they make the clicking/tapping noise, a high pitched noise in tune with the revolutions, or I've seen others where the belt starts to ride off the tensioner pulley. I'm sure there are other modes of failure for these parts, but I've not experienced those yet!

The belt seems to be riding fine on the tensioner pulley and it's not bouncing excessively (they all have a little shake). I'm thinking it's the idler pully but of course I'll know more once I have the belt off. There are various signs of failures for this pulley and I think mine is one of the less common. It's not a squeaking, or a loud whine but a rattling.

The belt has a 6 yr service life so I'm there. In any case I ordered everything this morning. $180 for the tools (Tq wrench, Torx) and the necessary parts. Gonna save about $150 vs indy.

Hats off to FCP Euro and eTork.

 

[BMWTurboDzl]

Turns out the idler pulley was the culprit. The grease was almost gone as I could hear the bearings fall as I slowly spun the pulley itself.

Not a bad job on the BMW N55. I recommend removing the fan shroud as per BMW procedure because it gives you a lot more room and the ability to apply some leverage. Especially on the fastner holding on the idler pulley.

 

[zzyzzx]

Turns out the idler pulley was the culprit. The grease was almost gone as I could hear the bearings fall as I slowly spun the pulley itself.

Would it possible to hear or see anything if you posted a video if this? I'm also wondering if there is any play in the bearings.

 

[BMWTurboDzl]

Would it possible to hear or see anything if you posted a video if this? I'm also wondering if there is any play in the bearings.

Yes it would be.

For an idea of what I'm talking about search YT for BMW Idler Pully Noise - Before & After /// 330i (E46). My vehicle is obviously decades newer but the pulley itself hasn't changed. In that video you'll get an idea of what mine sounded like.

While running I had a rattling noise which I thought was coming from the alternator (Idler pulley sits right underneath it). I have a video of that but I'd have to create a link for it and I don't have the ability to do so now. Ultimately I'm guessing the issue was the idler pulley due to the lack of sound with the new components and the condition of the pulley itself.

 

[zzyzzx]

Yes it would be.

For an idea of what I'm talking about search YT for BMW Idler Pully Noise - Before & After /// 330i (E46). My vehicle is obviously decades newer but the pulley itself hasn't changed. In that video you'll get an idea of what mine sounded like.

I was hoping that they would check for play on the old one, but yes this is helpful.

 

[BMWTurboDzl]

I was hoping that they would check for play on the old one, but yes this is helpful.

In my case both the idler pully and pulley on the tensioner had very little play.

 

[Cherrybomb]

A great catch.Its always better than breaking down.Now analyze your tools,and update those that didn't perform