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Old 02-23-2011, 10:24 PM
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bluebee bluebee is offline
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Location: San Jose, California
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Mein Auto: 02 BMW 525i M54 auto 130K
For the record, G. P. Burdell, over here, kindly provided a pointer to the following BMW alternator-belt tensioner retrofit service bulletin:

Originally Posted by G. P. Burdell View Post
There's a BMW service bulletin (SI B 11 04 03) that recommends replacement of noisy mechanical tensioners with hydraulic tensioners. The bulletin applies to most BMW models equipped with the M54 engine.
Thanks to Nando & Starless, attached below is a copy of that Technical Service Information Bulletin (I created the SIB JPEGs for ease of viewing).

Note the following BMW SI B 11 04 03 details:
  • It applies only to the upper tensioner on the M54 engine (alternator belt)
  • It applies only when a customer complains of noise
  • It requires a "kit" to allow switching from 2 bolts (mechanical) to 3 bolts (hydraulic)
    • Upper bolt: BMW PN 07 11 9 901 785
    • Lower bolt: BMW PN 07 11 9 912 652
    • Left side bolt: BMW PN 07 11 9 913 111

The question I would have is, since most cases of noise are in the bearings, not in the spring, what is in a so-called hydraulic tensioner that would cause it to be less noisy than a mechanical tensioner?

Note what cn90 said: Both are mechanical; one is a spring in oil, the other doesn't have oil ... but noise is usually from the bearings, which, presumably, both have.

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Attached Files
File Type: pdf BMW_July_2005_E39_SIB_110403_mechanical_to_hydraulic_tensioners.pdf (113.7 KB, 961 views)

Last edited by bluebee; 02-25-2011 at 06:11 PM.
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