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Old 01-21-2013, 08:49 PM
Supercourse Supercourse is offline
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Location: British Columbia, Canada
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Mein Auto: 2004 X3 2.5i
Originally Posted by awdrev View Post
Question regarding belt tensioners:

For anyone who has done either a full cooling system overhaul or the OFHG job, how do the belt tensioners work? Specifically, I know they have a little cap and that they are a TORX bit set, but I am wondering how much to tighten them when the job is done?
Be prepared for a few possibilities on how you release pulley tension and how the tensioners are bolted to the block.

With my 2.5 M54 the main accessory tensioner is mechanical, with a 16mm. hex head bolt release, and attached to the block by two 13mm. hex head bolts.
(The pulley itself is bolted to the tensioner with a torx bolt - T45 I think.
BMW don't consider this pulley to be replaceable, but it can be done with a Dayco 89133 pulley - less than $20 from rockauto.)

You may have the later hydraulic tensioner if a previous owner got it replaced, which will have torx bolts I believe.
And the pulleys for those are readily replaceable.
I think those were the torque values you referenced.
I would imagine about the same torque if you were replacing a pulley on a mechanical tensioner.

Even among the mechanical tensioners there may be differences in cover caps and how the tension is released depending on who the supplier was - INA, Febi/Bilstein, etc.

As a general rule, if the tension doesn't release easily with a c/w turn then you are in the wrong place.

The AC tensioner on an M54 is more likely to be a hydraulic type I believe. Not sure though.

(The N52 engine went to a single accessory belt, maybe because having an electric water pump made that feasible.)

There are also differences in how the air duct over the radiator is attached depending on engine type and/or model year.
Maybe even differences between the 2.5 and 3.0 - mine uses about 8 torx screws while others use plastic pins I think.
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