[sparkymarky]

RE: aux drive belt and tensioner change and idler pulley change.

As i could not find any info for the M57 anywhere on the net, I thought that after to'ing and froing to halfords for tools, i'd save others the hassle and post some useful info.

1. The aux drive belt tensioner (which has the long belt going around the air con pulley, water pump, alternator, crankshaft) is a T60 Torx to unlock it. A 1/2 drive T60 on a breaker bar and extension fits in there nicely.

2. Once unlocked, you will need a T55 torx bit to undo its centre bolt - a 3/8 drive one on a 3/8 extension and ratchet will fit nicely.

3. The idler/deflection pulley. Actually, I didn't check what size its centre bolt was, suffice to say if you have a cheapo set of allen key drive bits or even regular allen keys/hex bitslike i did, its a small to medium size, about a 6/7 so not a specialist size.

4. Ps, IF you want to change the long aux belt, you will have to also remove the crankshaft to power steering belt (bottom left as you look at front of engine) as its in the way of taking the aux belt off. This is tricky as there is no tensioner for this belt. It's a stretch belt, so you will need a stretch belt tool to take off (or snip it off)/get the new one on (screwdriver an option i guess but you risk damaging the belt and/or pulley £££). Plenty of you tube guides on stretch belt tools (and to remove that belt you will likely need the radiator fan shroud and undertray removed for access, but thats simple just time consuming).

[Tim G]

Since I have the M57 engine and am still very new to it, i must ask the question, why did you change it?

[sparkymarky]

Because the aux belt was starting to hang off the tensioner pulley by about two/three mm and would eventually flip and get caught in the other belt, potentially causing a lot of damage as they have a propensity to wrap themselves around the crank pulley when this happens...turns out it was just a new belt i needed as when I removed it both tensioner and idler span freely when I turned them- but as i bought a tensionet and idler in advance i fitted them anyway.

[Tim G]

Originally Posted by sparkymarky

Because the aux belt was starting to hang off the tensioner pulley by about two/three mm and would eventually flip and get caught in the other belt, potentially causing a lot of damage as they have a propensity to wrap themselves around the crank pulley when this happens...turns out it was just a new belt i needed as when I removed it both tensioner and idler span freely when I turned them- but as i bought a tensionet and idler in advance i fitted them anyway.

Ah, ok. I see you have a 2006 model, how many miles has your car done for this to have occured?

[sparkymarky]

80k, which is about right to change an aux drive belt on any car as they stretch over time no matter what the car. I emphasis as i have already eluded to, the issue in the end was the belt wearing with time- the existing tensioner and idler were actually perfectly fine. No need to worry. Just normal car maintenance.

[Dan-danGT]

I have a similar issue on my 330d i looked last night the aux belt tensioner is out of line. I.e the belt on that pulley is at least 1 rib different to the rest.
I can see the Bmw costing my a fair amount these next few months. Front discs and pads, belt + tensioner!

[Aragorn30d]

I've had this before on another car, and changing just the belt didnt fix it.

The new belt only lasted a few weeks and it threw that off as well.

On that, the bearing/bushing inside the tensioner arm had worn, and had allowed the two halves of the tensioner to move slightly out of alignment. Everything looked fine, span freely, no noises etc, until you compared the good and bad tensioner and you could see the angle.

I'd definitely recommend changing both parts if your in there doing this job, you really dont want to have it all apart again a few weeks later to fix it a second time!