Alternator belt squeal

[scottishpedro]

Hi all

I have a slight alternator belt problem.  The belt was squealing very occasionally in August when I was downshifting (change in torque or something?), so I took it to a garage near work to be tightened.  It duly flew off 2 days later (I think they loosened it!) so I got a new belt an learnt how to fi it myself.  I tightened it and it has been fine until a week or 2 ago.  It started squealing on downshifts, only for about 2 seconds at a time, and today it was a bit worse (it was a bit colder going home from work tonight).  Tonight I removed the belt; it looks a bit shiny neither side and the pulleys area bit smooth.  I tried tightening the bel a bit, and it's a bit better.  Interestingly it only squeals on downshifts with the heater fan on (and obviously lights).  Is it simply a case of the belt slipping?  Is it worth trying to roughen the sides of the pulleys slightly?  Is it possible the intermittent slipping has knackered the belt (smooth sides) and I should get another belt?

Thanks in advance

Pedro

[clipperjay]

Try torquing up some of the old bolts(alternator bracket) with added torque from the engine and sudden high revs it can cause the block to move abit if the belt looks past it, then change it. An old trick was to spray hair spray on the belt so there was a bit more friction to the belt to pulley I've never used it, but heard it works? 

[Seanl]

I'd check over all the pulleys first. Your mentioning alternator, but check the others too. By the sounds of it, one is worn, and stripping belts pretty quickly.

[scottishpedro]

Just had another look and it appears one side of the V shape on the belt is smooth and worn slightly out of shape, the other looks fine.  I would guess this points towards one of the 3 pulleys being out of shape. Looking at the alternator pulley, there is some rust and it's a bit narrow in one section. Would it be worth trying to sand/grind this back into shape then replace the belt?  If not can the pulley alone be replaced?

Out of interest, what causes the squeal/belt to slip.  I understand that the alternator demands more when more electrical items are in use (I turned on lights, heater, rear defroster and radio and the belt squeals when the engine is reved), but what actually makes the belt slip? Does the alternator pulley require more force or something under heavy load?

Thanks

Pedro