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Timing belt whine and hum...

2780 Views 8 Replies 5 Participants Last post by  Brit01
Does everyone get this on their 8V engines? I recently checked my timing belts and they seemed a little loose (worn themselves in since the rebuild) so I thought I would tension them up a bit. I tensioned them up to what the manual recommends and they made a heck of a racket, especially at about 1000rpm and a whine was detectable at speed once warm, which sounded cool :) but probably wasnt helping my belts (engine expanded = tightened belts = whine) so I loosened them off slightly and the noise has almost gone, still a slight hum at ~1000rpm. I figured if I loosen them off a little to what the manual says, as the engine gets hot (and expands) an acceptable tension should be reached.
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Did you check the bearings of your tensioners..?
i found you have to grease the back of the tensioner pulley bracket so when you release the nut the spring flicks it against the belt. otherwise the friction works against the spring and you have to keep guessing how much to load it up.
Tensioners were re-newed when I did the rebuild, and the grease behind the tensioner sounds like a good idea, but I still find the springs aren't quite enough, and need a tiny bit extra just as they are tightened.
I've known all 8V boxers to make some sort of a hum, probably just a natural resonance from the belt at certain revs:rolleyes:
Hi there.

I have also found my belts are a little loose. I can turn them more than 90 degrees. They were new about 15,000kms ago.

My tappets started making a noise recently and lost a bit of torque. Hoping it's not a tappet issue.
Heard it may be due to the loose belt (amongst other things).

Broke my cheapo wrench trying to undo the tensioner 17mm nut!!!

so I need to put a bit of grease behind. good trick.

Then undo the bolt and it should tighten them up a bit more if they are too loose no?

Shopping time for a decent wrench.
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This thread popped up towards the top of the list and I thought I might add another 2c worth...

Personally I think the whine and hum of the belts is a result of being too tight. The manual suggests to tighten the belts with its specified tension of I think 8mm up and down movement on the non-tensioner side of the belt. When starting a cold engine the belt hum is not noticable (cold engine) but as the engine warms up it starts due to expansion - how much the engine expands would be nice to know, but it must be a decent amount, enough to pull the belts really tight.

If you check the tension of the belts on a warm engine, they are really tight. My solution is to have a slightly more loose belt when cold (but not too loose) and when hot, is the correct tension resulting in no hum or whine. I cant help but think also that a slightly more slack belt at running temperature is less likely to suffer an unexpected immediate failure (read people with relatively young belts that snap after being set to 'right' tenion etc) I also check my belts on a regular basis to see how they are going.

Happy Easter all!
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Working by torchlight in the garage (it's a private rented one with 50 other cars!like a parking lot).

Lubricated the arm tensioners.
Removed all plugs.
Replaced the alternator belt.

Turned the crank using the alternator belt and hand on crankshaft pulley to tighten up the belt on the non tensioner side.
Pulled on the tensioner and locked in the nut!!

Same on both sides.

Checked timing. SPOT ON to the milimeter.

Replaced averything except the timing belt covers (painted them also).

Started her up and a sweet alfa came alive again. Couldn't get her out as I was in the middle of a storm!!
Anyway I idled her until she reached 85 degrees - revved her nicely and all sounded very smooooth.

Have to give it a test run tomorrow and make another video to see if you notice the difference.

As the alternator belt was off I felt the water pump pulley and it felt ok.
Was a fraction, just fraction of movement (milimeter range), but I think this may be normal.
Alternator bearing was also smooth.

Might just loosen the right blet tensioner a fraction - no whine or hum but it felt a tad tighter than the other side. As you said I don't want a snap when the engine gets really hot.
They expand quite a bit if you feel it when cold and hot.
I think when cold you shouldn't be able to turn it more than 90 degrees by hand without a lot of force.
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Make sure its not your alternator or water pump

Try it briefly with the A & WP belt off as they can feel fine but still be noisey. And it is easy to do
Wifey was driving the car tonight.

When she arrived back it was squealing. (she didn't even notice):eek::eek:

I smeared a little teflon grease on the inside of the new crankshaft pulley and squeak disappeared.

Had a custom made pulley lathed.

Seems to me it is rubbing slightly on the inside next to the timing belt when it gets really hot:(:(:(

So i'll have to remove this pulley, have a little lathed off from the inside I guess, new timing belts also to be on the safe side.

Is the inside of the cranshaft pulley supposed to be flat against the cranshaft? Or slightly curved outwards so as not to touch the edge of the outer cambelt?
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