M635 Air Con Compressor Belt Swap

[Boggie]

Hi All,

I am replacing all the belts on the car with new BMW items. The tensioners are a great design, with sawtooth track above the slot and a toothed 19mm 'nut' that walks along the track until the belt is tensioned and then locked off with the 13mm on the other end of the coach bolt that goes through it. All three of my tensioners (alternator, power steering and compressor) had worn sawtooth brackets and damaged toothed nuts so I have been replacing the lot with new BMW items.

Both the reconditioned alternator and steering pump now have all new brackets, fixings and belts but I am struggling with the compressor. Firstly the bracket is no longer available but I got around this by cutting out the damaged sawtooth, carefully cutting out the good section of sawtooth from the old steering belt tensioning bracket and welding it into the compressor bracket. Took all evening but it worked out well and have to say it looks great with a coat of zinc paint.

However, my smug mode did not last long as even with the compressor moving freely AND the adjuster bracket not fitted yet, the belt was a bugger to remove. I had to gently lever it off using a screwdriver! I suspected the belt must not be the right size so opened the packet containing the new BMW belt and found that my old one was the same part but the new one is slightly smaller, due to being new. There is no way I can get this belt on!

As I see it right now, I reckon I have two options:

• Remove the compressor top bolts or the whole bracket so I can tip the compressor to fit the belt (a challenging job with the car on jack/stands and no access to the RHS of the engine bay as it is against the wall).
• Find a slightly larger belt (but this might effect my ability to tension the belt as there was not much left on the rather short adjuster to allow for this.

Am I missing something? Is there a trick to it?
Thanks,
Ian

[ron]

I had the same problem Ian. With a bit of juggling I fitted the belt to the compressor before bolting it to the engine.

I think it took 3 hands!

[Boggie]

Thanks Ron,

How do you access the top mount bolts please? Can I do this from the underside of the car?

Ian

[ron]

I think I did mine with the radiator removed which made it a lot easier.

[Boggie]

Thanks Ron,
I have a lovely new Rad, which thankfully is still in its box. :)
However the aircon rad is still in place and I have no access to the RHS of the engine bay without moving the car. Is it possible to remove the compressor top mount from the underside or do I need to remove the bonnet?
Cheers,
Ian

[ron]

Probably easier to remove the bonnet. May well help at a later date for access.

[Brucey]

IIRC the compressor can be removed from below. Not easy whichever way you do it....

BTW V-belts are sold by length in motor factors. It may be possible to buy one that is a few mm longer; I have often found that the OEM belts on various cars are not a sensible length for easy fitting in situ, and a slightly longer one often works better.

BTW if you bought a new top bracket for the alternator you may have missed the opportunity to upgrade to a double-sided top bracket, as fitted to later M30 engines. A double-sided bracket is much better because it means there is less bending load on the (not very good) alternator mounting bushings.

cheers

[Boggie]

Thanks Brucey,

The problem is that the compressor does not have a lot of room to move so fitting a larger belt might mean that it cannot be tensioned properly so giving belt squeal when hitting the AC button. I managed by brute force to get the belt on using a stubby flat blade as a wedge and turning the crank pulley with a socket wrench. I also found being abusive and threatening helped...

Cheers,
Ian