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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N55 Turbo Engine / Drivetrain / Exhaust Modifications > N55 Belt Tensioner Jiggle. *Solved* Should I be worried?
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      04-18-2018, 07:04 PM   #1
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N55 Belt Tensioner Jiggle. *Solved* Should I be worried?

I noticed today that my belt tensioner is jiggling. Its not super fast, but it definitely shakes a bit. I am curious if this is normal? If it is not, how quickly should i change it?

I have a track day in 3 days and probably should figure this out ASAP.
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      04-18-2018, 07:20 PM   #2
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Quote:
Originally Posted by Insane435 View Post
I noticed today that my belt tensioner is jiggling. Its not super fast, but it definitely shakes a bit. I am curious if this is normal? If it is not, how quickly should i change it?

I have a track day in 3 days and probably should figure this out ASAP.
If you can fix it in time, I would. Unfortunately, I'm not sure if the "jiggle" is normal. But you're risking the cost of the HPDE cost if you don't fix it... Do it once with genuine BMW parts and it'll probably be good for the rest of the life of the car.
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      04-18-2018, 07:47 PM   #3
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I can't confirm if this is an issue you should be concerned about or not, but I noticed the same after an N55 engine replacement and the dealer said that it was normal. 4000 miles later it still jiggles the same amount but otherwise no issues.
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      04-18-2018, 08:03 PM   #4
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I think I am going to replace it and the belt, just to be safe. My real concern is can i track the car with the way it is.
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      04-18-2018, 11:02 PM   #5
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Quote:
Originally Posted by Insane435 View Post
I think I am going to replace it and the belt, just to be safe. My real concern is can i track the car with the way it is.
A new belt and tensioner aren't that expensive.

Just replace and be done - if only for peace of mind.
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      04-18-2018, 11:21 PM   #6
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Quote:
Originally Posted by terryd5150 View Post
A new belt and tensioner aren't that expensive.

Just replace and be done - if only for peace of mind.
I know, but im wondering if i can track the car before doing so.
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      04-19-2018, 10:32 AM   #7
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Careful with the drive belt!

N5x motors eat drive belts via crank pulley hub, and the belt gets pushed into the oil seal, and into the oil pan, and pieces get sucked up into the oil pick up. This is a VERY common problem. Esp people with leaky OFHG causing belt/tensioner failures.

Just replace it ASAP. Then go to the track and have fun w/o worry.
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      04-19-2018, 02:58 PM   #8
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I was able to get ahold of the parts locally and will install them tomorrow before i track. Nothing like last minute. I will report back and let people know if the shake was normal. We'll see what the new parts do, but even if its normal, its good to know i replaced these parts considering theyre a common failure.
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      04-22-2018, 11:14 AM   #9
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I replaced the belt and tensioner and can confirm the jiggle was NOT normal. The new parts are rock solid.
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      04-22-2018, 05:27 PM   #10
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Quote:
Originally Posted by Insane435 View Post
I replaced the belt and tensioner and can confirm the jiggle was NOT normal. The new parts are rock solid.
Thanks for the follow-up post. Guess I need to take a closer look at mine now
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      04-22-2018, 06:41 PM   #11
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Thanks to the post, I noticed the same thing while my oil filter housing was leaking. Service scheduled!
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      04-22-2018, 07:27 PM   #12
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No problem! It's pretty crazy that this part decides to start failing so early, just like the E90. Its also a different part as well! I don't understand why it happens, but for $100 it's worth fixing around 50-60K and never having to worry about it again.

I guess it's time to start thinking about the front control arms, as I'm sure those need replacing soon as well.
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      04-23-2018, 11:59 AM   #13
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When you say "jiggle" do you mean lateral movement? Like side to side? Mine "jiggles" vertically but isn't that normal?
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      04-26-2018, 01:14 AM   #14
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Here's a video of my "jiggle", is this anything to be concerned about?



fast forward to 0:25
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      04-26-2018, 02:44 AM   #15
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My N55 x3 2011 developed a OFHG leak and soon after the belt tensioner and one of the idler pulleys started making noise at off load low revs around 1100rpm. It ended up getting worse pretty quickly.

Anyone replacing the tensioner I'd advise to replace the idler pulley as well. The old idler pulley basically had 0 bearings left.
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      04-26-2018, 06:36 AM   #16
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Quote:
Originally Posted by badbread View Post
Here's a video of my "jiggle", is this anything to be concerned about?



fast forward to 0:25
Doesn't look right to me, I think bearings may be dragging and pulling on tensioner spring. Best way to tell is swing tensioner clockwise and pull belt off pulley. With no load on it grab pulley and check for play in the bearings, if there's any movement at all it's shot. Might as well check idler pulley too while belt is loose.
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      04-26-2018, 10:53 AM   #17
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Quote:
Originally Posted by Insane435 View Post
I replaced the belt and tensioner and can confirm the jiggle was NOT normal. The new parts are rock solid.
glad to see you got it replaced.
you have any diy for replacing it or is it fairly easy to do so?
Thanks
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      04-26-2018, 11:12 AM   #18
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Insane435 can you confirm after replacing it, it doesn't jiggle like in my video above?

Thanks!

**Edit

Would this be covered by the CPO warranty?
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      04-26-2018, 11:17 AM   #19
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Quote:
Originally Posted by VT-man View Post
glad to see you got it replaced.
you have any diy for replacing it or is it fairly easy to do so?
Thanks
It's super easy. 30 mins-60 mins

1) Make sure the car is cool.
2) Grab a T50 and torque wrench, turn tensioner CLOCKWISE to release tension.
3) Walk the belt off the pulley near the tensioner or alternator, whatever is easiest.
4) Unbolt tensioner with an E-torx (its like an E10 or E12). You can also use an equivalent size MM socket. Just find one that fits snug.
5) Reinstall new tensioner. You CAN reuse the same bolt. It is NOT a one time bolt like on the E90. I confirmed this beforehand and can say that its NOT an aluminum bolt when i did the install.
6) line up the new belt. I found that you need to get it around the big pulley on bottom left first. The last part I wrapped it around was the alternator.
7) Grab the T50 and torque wrench and turn tensioner CLOCKWISE and pull the pin out of the new tensioner with channel locks. I did this step by myself, very easy. The tensioner is now loaded and you're done.

NOTES:
I did not remove the fan shroud. This would give you more room, but is not required.
I loosened the oil feed line 10MM bolt to be able to move them a bit if needed.
***When you reinstall new tensioner, its sits very different. The pulley is off to the left. This is normal. Once you remove the pin in step 7, it will sit up and down like normal.
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Last edited by Insane435; 04-26-2018 at 11:20 PM.
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      04-26-2018, 11:29 AM   #20
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Quote:
Originally Posted by badbread View Post
Insane435 can you confirm after replacing it, it doesn't jiggle like in my video above?

Thanks!

**Edit

Would this be covered by the CPO warranty?



He confirmed no jiggle after replacement on post #9 but I too would like to know if covered under warranty. I actually just had my belt replaced under warranty as it was fraying, I'll try to see if they'll replace the tensioner.
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      04-26-2018, 12:18 PM   #21
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FWIW, just called the dealership, their warranty administrator claims she's 95% sure it would be covered by CPO.
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      04-26-2018, 01:07 PM   #22
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Quote:
Originally Posted by Insane435 View Post
It's super easy. 30 mins-60 mins

1) Make sure the car is cool.
2) Grab a T50 and torque wrench, turn tensioner CLOCKWISE to release tension.
3) Walk the belt off the pulley near the tensioner or alternator, whatever is easiest.
4) Unbolt tensioner with an E-torx (its like an E10 or E12). You can also use an equivalent size MM socket. Just find one that fits snug.
5) Reinstall new tensioner. You CAN reuse the same bolt. It is NOT a one time bolt like on the E90. I confirmed this before hand and can say that its NOT an aluminum bolt when i did the install.
6) line up the new belt. I found that you need to get it around the big pulley on bottom left first. The last part I wrapped it around was the alternator.
7) Grab the T50 and torque wrench and turn tensioner CLOCKWISE and pull the pin out of the new tensioner with channel locks. I did this step by myself, very easy. The tensioner is now loaded and you're done.

NOTES:
I did not remove the fan shroud. This would give you more room, but is not required.
I loosened the oil feed line 10MM bolt to be able to move them a bit if needed.
***When you reinstall new tensioner, its sits very different. The pulley is off to the left. This is normal. Once you remove the pin in step 7, it will sit up and down like normal.

You are the man!
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