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Discussion Starter #1
I'm not sure if this was already mentioned here but I will share anyway.

Just after the purchase of my 840 I have changed all the service items including drive belts - all parts were picked from BMW garage and a local shop by reg plate number.

Since the service I could hear from time to time a squeak from one of the belts - now I know it was the longer one driving the power steering pump.

There was no further adjustment on the tensioner and the belt was still slack.

Now it appears that some of the shops (including shops online) offer belt 7K X 1605 (1605mm long) instead of 7K X 1580 (1580mm) which according to RealOEM is the correct one for Great Britain.

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RealOEM.com   BMW E31 840i Belt Drive Water Pump/Alternator
New - correct belt now fitted - right on time as I was just to buy new tensioner for £80 which will not sort the problem anyway.
 

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As far as I know 1605mm is the correct length for UK cars fitted with the M60 engine. It was only the Gulf version and Hot Climate versions that use the shorter belt. The reason for this is that those versions use a smaller water pump pulley to increase the speed of the water pump and viscous-coupled fan:

RealOEM.com   BMW E31 840i COOLING SYSTEM-FAN/FAN COUPLING
 

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Discussion Starter #3
Timm,

If you open link to RealOEM from my previous post and check the lowest line for the item no. 1 (belt) it says NATIONAL VERSION GREAT BRITAIN - 7K X 1580 which supports my theory. New belt (1580mm) fitted and all ok - its in mid range on adjustment screw
 

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Just for the record I had the same issue with a 1605 length belt - it fits but is a bit slack.
I had mine swapped for the 7k 1580 and it fits perfectly.

My alternator was new - its a Bosch 140a. The pulley on the alternator must be the right diameter as works with this belt.

Date - 17/10/2016
 
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