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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Is this normal? Serpentine belt tensioner vibration/bounce



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      12-13-2014, 05:19 PM   #1
Opo
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Exclamation Is this normal? Serpentine belt tensioner vibration/bounce

Hey guys,

2007 335i (12/2006 build date)
JB4, DCI, DP's
Car is at 190k KMs, no idea the last time the belt was replaced

So my car was making the slightest belt squeaking noise @ idle, so I inspected the belt. Looks great, no little cracks in it, looks pretty new (I've owned the car for the last 40k KMs and haven't replaced it yet.. I have plans to do so in the spring..)

I then sprayed some belt protector on it and the squeak went away, great.

Went out for some shopping/errands and the squeak comes back with a vengeance and makes my car sound like a $500 winter beater lol at all ranges of the RPM gauge..

So I get home and I filmed the belt tensioner because I don't want the nightmare belt shredded, get eaten by the crank pulley and pulled thru the front crank seal bullshit to happen to my n54...

Is this vibration/bounce at idle normal?



Then I had my gf rev it to 3k while I filmed the tensioner... Everything look normal?

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      12-13-2014, 06:00 PM   #2
Miller335
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I've never looked at mine on my 335 but I know with my other vehicles they bounce a bit, that's kind of the nature of auto-belt tensioner.

I can't say if yours is excessive but with your mileage I would replace the tensioner and all idler pulleys.
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      12-14-2014, 04:03 PM   #3
DJtoad
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That's an excessive amount of movement and I wouldn't be surprised if your tensioner is bad. Also, you can't judge the condition of a serpentine belt by looking for small cracks like you could with the old v-belts. They don't typically show wear and often look nearly new even when they're in need of replacing. You have to use a groove gauge.
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      12-15-2014, 06:51 AM   #4
Opo
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Exclamation

So I did some deeper digging. Turns out my alternator pulley is seized inside of itself (the clutch function) and I am replacing it.

Belt, tensioner, and idler pullies - I'll replace in the spring

Anyone reading this though be careful if your belt starts making any noise make sure you inspect it thoroughly and find the cause - my friend neglected his 335i belt noise and it shredded the belt, got sucked thru the front crank seal and jammed up the timing chain and belt his valves. Turns out his alternator was also the cause of his belt shredding. Both of our power steering pullies were un-touched by the sub frame.

Some helpful alternator videos:




Last edited by Opo; 12-15-2014 at 07:58 AM.
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