What is this part, and why does it rattle

[10then34]

Car sounds like it is shaking apart. Looked under the hood and the noise seems to come from the part labeled in red below. It shimmys back and forth against the engine block with the engine at idle.

What is it ?
Why is rattling ?
What does it take to fix it ?


Please tell me that it just holds on the dilithium crystals in place and that tightening the gulbinator garglesprings will instantly get rid of the noise. Oh, and tell me that it is a cheap fix.

 

[20IndigoBlue02]

part of the tensioner assembly for the accessory belt

 

[Seatman]

Alternator pulley is most likely seized and that is the tensioner probably bouncing like crazy at idle?

The pulley on the alt should clutched so it free wheels in one direction but not the other, when they go bad they lock up and are no longer clutched and that causes the tensioner to go nuts.

Check it out on youtube to see what I mean.

 

[10then34]

Ha! Explains the shiny belt.

Thanks for giving me something to work with. Sounds doable. 190k miles, I guess at some point a idler is going to wear out.

My Bentley manual doesn't address the tensioner replacement. I assume the idler/tensioner comes as a combined assembly.

 

[MyAvocation]

Correct. Get a new alt pulley and the special R&R tool.

 

[10then34]

Correct. Get a new alt pulley and the special R&R tool.

Now you have me curious. What is the 'special R&R tool' ? The pin described in the manual to lock the tensioner in the slack position ?

 

[Vince Waldon]

It's your alternator pulley that is probably locked and causing the problem, not the idler pulley.

And, removing and replacing the alternator pulley requires a splined driver.

Alternator pulley is most likely seized and that is the tensioner probably bouncing like crazy at idle

Get a new alt pulley

The easiest way to test the alternator pulley is to:

- unhook the serp belt from the alternator pulley
- lock the alternator fan in place with a screwdriver or other pointy thingie inserted thru the alternator body housing
- grab the alternator pulley by hand and twist it in both directions... it should spin freely in one direction and lock in the other

For more info you could search on "alternator pulley"... common problem, lots of threads and discussion.

 

[10then34]

Is the pulley bolt T50 or M10 triple squared ?

Why does it need that ratchet pulley in the first place ?

 

[Vince Waldon]

Is the pulley bolt T50 or M10 triple squared ?

Could be either, AFAIK, which is why the tool comes with both. Part MN3400, half-way down the page:

http://www.metalnerd.com/cat05.htm

Why does it need that ratchet pulley in the first place ?

https://youtu.be/rXehCcNzq_A , among others.

 

[10then34]

It's your alternator pulley that is probably locked and causing the problem, not the idler pulley.

Turns out both were trashed. The alternator pulley was locked and the alternator front bearing was noisy and had excessive play. The idler arm had lots of side-side play and poor tension. A box of parts and some time under the hood and I am back in business.