Author Topic: Worn belt pulleys? (Read 2753 times)

gravyface · « **on:** November 22, 2011, 06:44:35 AM »

So I got lazy and had a shop a few units down from my office replace my belts last July (power steering and alternator belt; AC was "new").

Fixed the squeal, idle smoothed out (not entirely, but was better).

Squeals back, bring it back, guy says he'll adjust them as he thinks they're too loose; I pushed down on them fairly hard and would barely budge an inch.

So he tightens them (I mean the rack tensioner is at the very last tooth) and the squeal is gone, but the alternator belt looks glazed and seems to be sitting pretty deep into the groove. He suggests that the pulleys are likely worn and should be replaced.

Searching around, I don't see any instances where people have replaced their pulleys; I have high mileage (640k KMs), but just doesn't seem like a wear item to me.

Also, how tight should these belts be? Can't find a good rule of thumb or a method to test the tightness anywhere.

Seeing that tightening up almost new belts (probably put 1000 KM on it since July) leads me to believe that perhaps they're the wrong belts? Or maybe it really is the pulley?

I'm going to do it myself this weekend and replace all 3 belts again, but I'd like to take my time and inspect the pulleys (I guess make sure they still have a "V" shape and are not rounded/dished?) and get the belt tension perfect.

vpilarry · « **Reply #1 on:** November 22, 2011, 07:24:46 PM »

Its highly doubtful that a rubber belt would wear a metal pulley. I found that 1 size shorter (1/2" shorter IIRC, 40.0" instead of 40.5" or 1015mm instead of 1025mm) alternator belt than that listed in catalogs fits the best.

Best way I found to check tension is to twist the belt with your bare fingers - you should only be able to twist it 1/4 turn (90�) without straining hard. If it twists more = too loose, twists less = too tight.

DesktopDave · « **Reply #2 on:** November 22, 2011, 07:53:30 PM »

IMHO your belts are too tight. I usually just press the belt in on the longest span. If it deflects about 3cm (1inch) it's usually OK. New belts are always overtightened, as they tend to stretch.

Is the belt visibly bulging? The belt's outer surface should be flat, not sinking into the v-groove and wearing along the outside surfaces.

Could very well be a bent mount. My P/S pump was definitely twisted when I removed it. A few degrees of mis-alignment will cause squealing no matter how tight the belt is. Also could be the pivot bushings, especially on the alternator mount. They're not too expensive. My alternator belt is also slightly long, I've never bothered to fix it as it makes no noise.

I tried out the Dayco ribbed belts this time, they've been working very well. My pulleys are glazed but the belts ride in them correctly. On other cars I've used "belt dressing" as a quick & cheap fix.

gravyface · « **Reply #3 on:** November 22, 2011, 09:10:29 PM »

Quote from: DesktopDave;108261

IMHO your belts are too tight. I usually just press the belt in on the longest span. If it deflects about 3cm (1inch) it's usually OK. New belts are always overtightened, as they tend to stretch.

Is the belt visibly bulging? The belt's outer surface should be flat, not sinking into the v-groove and wearing along the outside surfaces.

Could very well be a bent mount. My P/S pump was definitely twisted when I removed it. A few degrees of mis-alignment will cause squealing no matter how tight the belt is. Also could be the pivot bushings, especially on the alternator mount. They're not too expensive. My alternator belt is also slightly long, I've never bothered to fix it as it makes no noise.

I tried out the Dayco ribbed belts this time, they've been working very well. My pulleys are glazed but the belts ride in them correctly. On other cars I've used "belt dressing" as a quick & cheap fix.

There's Daycos on there now. He did say that he thinks that the pulleys are misaligned. I have noticed that, when it's not squealing, the idle seems to improve: car never stalls, but when the clutch is disengaged at a stop sign or whatever, it tends to bog a bit as it drops below 800 rpm and climbs back up again. Not sure if that's something else (vacuum leak, etc.), but I could swear that the idle improves when the belts are a bit happier.

DanOKC · « **Reply #4 on:** November 24, 2011, 06:53:25 PM »

Make sure the belts are same width, a skinnier belt will ride lower in the pulley. I replaced my AC belt & was in a hurry, didn't order online from usual sources. I had to make 3 trips to
O reillys before I got the right size. I was buying Gates, their best brand, but they cross the size & come up with a belt that is 9.5mm wide or some such nonsense. On real OEM, all the belt sizes are speced as 10mm for M42.

I also had a good BMW parts place in CA once tell me they sell a wider belt for E28's when I bought belts for that car one time. They said BMW spec is X but we use this next size wider, they last longer.