Noisy pulley - chuga chuga chuga with video

[318touring]

Seems that one of my pulley is noisy. I have just changed the water pump-last week (hopefully NOT the new water pump making this noise), and belt was replaced 2000 miles ago. What do you think? Or maybe alternator bearing?

[Ahsai]

~12 times/second so close to crank speed at idle. Sounds like a very dull noise. Maybe it's just your hand shaking but the belt looks like it's wobbling slightly?

Have you tried removing the belt and hand spinning all the pulleys and accessories yet? You could even turn on the engine to check for noise w/o the belt for a minute or two should be fine.

[318touring]

LOL, youtube offered an enhanced version of the video where it wasn't shaking. It was my hand shaking not the belt :-)

I'm going to take the belt out on the weekend and move the pulley one by one. It's getting darker and colder earlier now since it's autumn at this part of the world.

[Ahsai]

Lol, I think you'd rather it be your hand. Btw, I counted wrong...should be about 3/ second so really slower than the crank pulley.

[perryinva]

If you look & listen carefully at the video the 'flump flump flump" matches exactly with the lettering of the timing belt in the video, so it is no pulley bearing at all, as they all rotate more than one revolution for each belt revolution. You may have gotten some grease or oil on a section of the belt, transfered by a pulley or something of that order. Remember both sides of the belt have contact with pulleys, so it could be on either side, though I'd bet on the smooth side myself. The belt path is torturous and there are 3 smooth back side idler pulleys. The new WP may not be exactly in line with where the old one was so the belt takes a tiny jog in or out to correct itself each revolution by sliding (flump), since it is for sure not in the same physical contact points that it was originally. If it bothers you that much, try a new belt and really clean the pulley surfaces. It will likely be gone, or changed.

Edited May 13, 2013 by perryinva

[Doohan]

It could be some air trapped in the new water pump....

[318touring]

Thanks guys.

I'm sending it back to the garage who did the WP change, the car needs its 6-monthly road-worthiness testing tomorrow anyway. I'll post here what they found out.

I ended up not taking the belt out due to the above.

[318touring]

Seems the tech is sure that 99% the top idler pulley is the cause.

However annoyingly the car fails its MOT due to torn top struts, http://www.design911.co.uk/fu/prod13732/Shock-Absorber-Top-Strut-Support-Porsche-996-C4---Turbo/

And there is excessive play on the lower arm ball joint, http://www.design911.co.uk/fu/prod126919/Control-Arm-with-Lower-Ball-Joint--Coffin-Arm--Porsche-986-Boxster-and-996---04_2/

I am looking at the right replacement parts, correct?

Edited May 15, 2013 by 318touring