I can see how to replace the main outer drive belt for water pump, power steering pump and alternator - apply leverage via large torx key in belt tensioner and remove belt. Probably wise to make a diagramatic layout sketch before hand to assist on reassembly. I have done belt replacement on an E39 525i which is more difficult with fan removal etc.

But the inner air conditioning belt does not have a tensioner to relax. I don't imagine that the belt is simply cut off and a new one rolled on by attaching first one end to A/C pulley and rotating other end onto crank shaft pulley as this could damage the belt. Loosening the A/C compressor mounting might be the way - does anyone know the proper procedure?

 

There is not a tensioner for the a/c compressor. After you cut off the old belt, you start the new as you discribed and then you attach a special tool to the a/c compressor pulley and then rotate the crankshaft - presto, it slips right into place. I did this a couple of weeks ago and it works. I did not have the special tool required - I made one by modifying a small tube cutter.

 

I have managed to find information (basically as previous post - thanks) as per attached poor quality pdf. It makes me wonder that if you can pull the belt off as instructed, whether a replacement could be wound on pressing and keeping edge of belt on A/C pulley in place as the engine pulley is cranked round at central bolt.

Come to think of it, I have an old tube cutter for copper pipes with cutter and two rollers that can removed that might work if it doesn't get in the way of anything. Also some miniature 'G' clamps.

 

You don't need to cut any belts in order to remove them. I changed my alternator earlier today and replaced both the a/c belt and the alternator belt as well. It is exactly how you explained it with your e39. You will use a torx socket to relieve tension on the belt. One for each belt. You will not be able to see the torx bolt until you pop the caps off of the tensioners that cover the torx bolts.

 

I removed my fan when doing this because the alternator had to go. I'm not sure if you have to remove the fan or not to replace only the belts. If you didn't it would be a pretty tight fit atleast from what I remember with my M54 engine

 

bmdub, my E61 N62 V8 does not have an A/C belt tensioner nor a water pump driven viscous fan like your M54 (or my previous E39) may have. So there is a bit more room, in fact I believe there is enough room for a V10.

The tensioner on the N62 requires either a T60 or T70 Torx Star 1/2" drive bit (mine are by Draper). I haven't yet done this, but on my E39 M54 the tensioners were relaxed with a hex socket and a drill bit inserted through lined up holes to hold in place. This enabled two hands free to remove and reinstal belts. BMW suggest that the relaxed tensioner is secured with a special tool - a drill bit of the correct size might suffice.

 

Here are some pictures of the tool I made and how it works - hope this helps.

 

Excellent tool! In practice it has to be over the belt to force it on when you turn the crank pulley. I have managed to get better PDF of the official instructions.

 

awesome info ! i'm thinking of replacing my belt because it started squeaking after i applied some belt conditioner(prestone). i wanted to take care of the belt but ended up messing it up-sucks, reminds me of some veterans advice"if it's not broken, dont fix it".

 

Anyone know the size of the torx key needed for this?

Thanks,
John