406oc.co.uk

One for our resident mechanics I think

If something (let's say the alternator, although it could be anything) is seized, how long would you expect a belt to last?

As you may have guessed, something on my bimmer was making a right noise changing pitch with revs when I drove it home the other day, but I couldn't tell what. Today I fire up the engine to see what it is and the noise is now (literally) deafeningly loud. My guess is something's seized. I really don't want to stick my head down there, or even leave it running long enough to do so, so I dunno exactly which expensive bit it is. Can't see how I can get tools on the tensioner either without removing the fan, and with the 406 occupying the garage I can't do any work lasting more than a few minutes before the sunlight goes.

So should I chance driving it for 10 mins to a garage, or should I cut the belt (hoping it's the alternator/pas belt, not the AC belt making the noise) and hope the battery gets me to the garage if I stay under 1000rpm?

If you had a seized alternator the battery light would be on as you will have zero charge.

The tensioner could have seized, but it's all guesswork unless you can look at the belt to see what pulleys are turning.

mjb wrote:I really don't want to stick my head down there

Use a short piece of tube such as the cardboard tube out of a roll of clingfilm/foil like a stethoscope to direct what you're listening to?

jasper5 wrote:If you had a seized alternator the battery light would be on as you will have zero charge.

I'm pretty sure it seized after it cooled following the noisy drive home. I didn't let the engine run long enough today to tell if the light's on. Won't be able to do that now until tomorrow evening - it's too loud to try it now or in the morning

The tensioner could have seized, but it's all guesswork unless you can look at the belt to see what pulleys are turning.

I wanted to get to the tensioner so I could slacken the belt and turn stuff by hand.

Really, I'm hoping it's the PAS pump, which (according to the Wheeler Dealers M5 episode) might be accessible from underneath without dismantling the cooling system, unlike the WATER COOLED alternator which from a quick look might even need the AC disconnecting from the condenser. Water cooled alternator! WTF? Really? Bastards! But yeah, I think the PAS pump's damaged anyhow given the steering gets bloody heavy when the fluid's allowed to get hot (urban driving in summer afternoons, or half hour with the engine off following a long drive) so I hope given it's the lowest pulley, it's that which is knackered following the drive through flood water the other weekend letting water get into its bearing

Could well be the bearing that got the flood water in it.

I'm not familiar with the tensioner on those, so not sure how to access it.

You should be able to get it to the garage with a fully charged battery, I got a van from Manchester to near my house (30miles) with a dud alternator.

jasper5 wrote:Could well be the bearing that got the flood water in it.

that's my thinking...

I'm not familiar with the tensioner on those, so not sure how to access it.

it's like the 406 v6 - pivot on the engine, attached to the pulley by a big spring. Actually 2 pulleys, but I can't see it making a difference. The pain is the screws are quite recessed and access is restricted by the top rad hose, some other hoses and of course that damn fan.

Hope the weather gives me a chance to have a go at it over the weekend, but it's not looking good

jasper5 wrote:You should be able to get it to the garage with a fully charged battery, I got a van from Manchester to near my house (30miles) with a dud alternator.

With 8 spark plugs to power I'd expect somewhat less than that, but I can't think it'd be too much worse, although I suspect one of my suspension bags has a leak so the air pump might fire itself up. We'll see... I might just be able to juggle things around and get it into my garage in which case I'll be fine provided I don't have a belt snap in my face

I don't think I'd drive it squealing like a Pig, although some would I guess, what about soaking things with WD40? that might buy you a few miles, or breakdown* and get it towed?

I wonder if you can turn the engine by hand (whip* the plugs out?) and try to see if anything won't rotate with the rest of the stuff?

What sort of noise is it?

This is what my car sounded like when the bearing went on the tensioner.

the sound's either a loud buzzing, or an aerosol fog horn (yes, THAT loud!)

just managed to get a look before it started pissing down, and everything appears to be spinning tried spraying wd40b in the direction of the alternator and pas pump (contaminated the belt in the process - grr) but it made no difference. It could be an idler, or maybe the fan coupling (the fan being big and light enough to cause such a loud noise) but until I can get the belt off, there's no way of knowing.

I think I'm going to have to cut the belt to diagnose it because access to the tensioner and the weather are against me here. will it take my hand off if i cut it with a stanley knife?

One thing you could try is to pull back the tensioner before you decide to cut it.....use a hacksaw blade if you decide that...if the belt has a long section try pulling the belt to push the tensioner back and jam it with something, enough to allow removal off any pulley even by levering.

Woo! Got the car into the garage, bought a 32mm spanner and 4lb hammer and got the fan off. Not too hard with the right tools

That gave me clearance to get to the tensioner (thank god I have a set of deep sockets - my extensions are too long) which let me take the belt off. God knows how I'm going to get that monster belt back on but hey.

In a nutshell, the tensioner pulleys have a little play in them and one spins freely but sounds a little rattley. The PAS pump has a strange clicking feel to it (possibly the broken plastic impeller I suspect it has). But the alternator... is tight, grindy and makes a noise/feeling which makes me think it's the rear bearing that's shot. So I think I've found my immediate problem!

Just got to figure out how to drain the coolant (f**king WATER COOLED ALTERNATOR?!?! WTF?!?) and get the bugger out. Thankfully I have an alternative to the HBoL - two 2-inch thick volumes of the Bentley manual. Damn it's good

Sadly, the best I can find is will set me back about £450 for a recon unit

Sounds like it's just a bearing that's failed. In which case why don't ou take it to an alternator specialist and she if they can repair it?

I have a mate who is an alternator and starter motor recon specialist, If you don't get the bearing replaced let me have the reg number and I'll price up the job for you.

Bailes1992 wrote:Sounds like it's just a bearing that's failed. In which case why don't ou take it to an alternator specialist and she if they can repair it?

Thought about investing in a puller and seeing if i can acquire replacement bearings (BMW discontinued them), but I'm under tight money and crucially time constraints. I'll still be having a look at the thing at some point in the future though, see if I can recon and make some cash back

Alternator bearings are usually a standard bearing available at normal bearing suppliers for about £3 each.