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.
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
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.
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.