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Thread: Mechanical tensioner with idler pulley confusion

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    Mechanical tensioner with idler pulley confusion

    So my 1999 e39 528i wagon had a hydraulic pulley and when it started to make noise i bought a new one not realizing that i had bought the mechanical one. Thankfully it fits fine on the car but I heard somewhere that cars that came with a mechanical tensioner didn't have idler pulleys. Any of you guys know if i should keep the idler pulley on?

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    Where did you hear that? How else can you keep the belts tight?


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    Who needs the belt

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    So your replacement is just fixed-tension and doesn't have the spring shock? As long as it all fits, it should be OK but the other one is far more desirable for 2 reasons - you get 'perfect' tension (no need to worry about too tight / too loose) and it 'self adjusts' vs. a fixed tensioner. If you bought your tensioner from FCPEuro you could just send it back and get the right one, even if it was used! #yetanotherFCPplug
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    Quote Originally Posted by geargrinder View Post
    So your replacement is just fixed-tension and doesn't have the spring shock? As long as it all fits, it should be OK but the other one is far more desirable for 2 reasons - you get 'perfect' tension (no need to worry about too tight / too loose) and it 'self adjusts' vs. a fixed tensioner. If you bought your tensioner from FCPEuro you could just send it back and get the right one, even if it was used! #yetanotherFCPplug
    They both exert tension. One exerts it via a spring, the other via a hydraulic cylinder. Bmw used both on I6s. Pattern seems to be automatics got the spring from the factory while manuals got the hydraulic one, but there are exceptions to both.

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    geargrinder is offline Having No Trouble Here BMW CCA Member
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    Quote Originally Posted by TerraPhantm View Post
    They both exert tension. One exerts it via a spring, the other via a hydraulic cylinder. Bmw used both on I6s. Pattern seems to be automatics got the spring from the factory while manuals got the hydraulic one, but there are exceptions to both.
    Ahhh I thought he meant he got some kind of fixed-tensioner. Nevermind. Don't change it, should be fine.
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    The "hydraulic" tensioner is a regular coil spring in an oil-filled chamber, with a rubber cap. The roller assembly pivots on a pair of grease lubricated needle bearings. At this age, the factory assembly probably has a split rubber cap and gummy or dried-out grease.

    The "mechanical" tensioner is a large torsion spring. The spring is operated dry, with the two half-cylinder castings contacting each other. This sometimes results in an annoying squeaking. The spring is also vulnerable to rusting, especially if you don't have the under-engine "splash cover" installed.
    Last edited by djb2; 09-23-2018 at 11:10 AM.

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