BMW Idler Pulley

[ryankokesh]

So yesterday I noticed a new sound coming from the engine. I'm by no means an expert, but I'm fairly certain it's the idler pulley. Even if it's not, I'm pushing 115k and I don't have a record of this ever being done. So I think it's probably time either way...

Anyway... my question is actually about the A/C pulley. Should I go ahead and swap out this pulley and belt too while that pita fan is out?

thanks,
ryan

**Also**
Would I be able to easily tell if I had the hydraulic tensioner? Like I'd be able to see that hydraulic tube by the alternator, right?

[danewilson77]

I recommend you do:

1. Idler
2. Hydraulic tensioner
3. Serpentine belt.
4. Mech AC tensioner
5. AC belt.

Bout $100.00................

GLWM

[ryankokesh]

Is it worth it to convert it to hydraulic? Or should I stick with the mechanical tensioner?

[danewilson77]

I think its worth it. I did this on the 325I ZSP.

Some info in the DIY section here.....

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[ryankokesh]

Thanks, Dane!

....you're always costin me money...lol

[danewilson77]

Sorry...all the parts should be $100?

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[ryankokesh]

Haha, no worries. The conversion kit is like an extra hundred, but I'd rather do it the right way the first time than go back and do it again! Thanks!

[aurelius]

Let's wake this up for the uninitiated...

To those of you still in the 55-65k mileage range: replace your idler and tensioner pulleys. HERE'S WHY you want to do this. <<--His idler pulley failure was the earliest I've heard of (57k mis) but I have a family member whose same pulley seized at 67k. I replaced mine on a preventive basis at 63k and it was extremely worn. At which time you may as well also replace the serpentine belt since it will be removed. All of which can be done for about $60 in parts. Price dependent, as always, upon where you buy the parts.

Note 1: the DIY linked in the above paragraph involves a 2001 330i with a mechanical tensioner pulley. As such, the guy chose to replace the whole tensioner & pulley unit. Later E46 models (and seemingly all ZHP models?) appear to have the hydraulic version, on which the pulley wheel itself can be removed and replaced.

Little known fact but the same is true of the pulley wheel on the mechanical tensioner. That is, it can be replaced without replacing the whole unit but it is not the same pulley as goes on the hydraulic tensioner. But as noted earlier in this topic, the better option is to replace the whole mechanical unit with the hydraulic.

[Dave1027]

How about removing the tensioner, clean out bearing with PB blaster and air compressor, then repack with bearing grease? I did that on a Honda once. Solved the squeaking noise and work fine till I sold the vehicle some 5 years later.

[aurelius]

I imagine that would work just fine but the 2 pulleys in question are relatively cheap @ about $45 for the pair (OEM brand: INA @ Pelican Parts). About half that for their cheaper option. Much more for the BMW-branded pulleys, the vendor of which is reported to be INA.

For reference:

Idler pulley (all E46): 11-28-7-841-228
** some non-E46 models with M54 motor do not have an idler pulley. For example, the Z4.

Tensioner/Adjusting pulley: 11-28-1-748-131 (for hydraulic-style tensioner only) There is no known pattern as to which M54's were fitted with which of the 2 tensioner units. To ID which you have, search around or see photo below.

I shot WD40 into my idler when I knew it was due for replacement and did not yet have a new one on hand. Note to those who would do the same: I would not do this and assume you're ok for another 50k but do take the dust cap off if you do so and replace it afterward. If your pulley dust caps are missing, they can be purchased separately and do not automatically come with new pulleys. So don't toss your old caps when replacing the pulleys.

The metal cylinder with black plastic dust cap in the middle of the photo indicates hydraulic tensioner. It is below the thermostat housing, which is the overexposed piece at the top of the image. These parts are harder to see if you have a mechanical engine fan, which you do if you have an automatic transmission.