Fan belt/alternator problem

[JanXe]

Hello guys - I'm new here and I have a problem that's really driving me mad. I'm probably not the smartest guy around when it comes to engines, but I've come to a point where I have a big disagreement with my local garage and I need som help to solve this (please also excuse my halting english):
I had to change the alternator some six months ago and my local garage replaced it with a new one, supposedly to fit my engine (1992 6.2 L Diesel). Mounting the alternator was no problem but I soon found that the fan belt went "slack" (as apposed to thight). I thightened the belt, it was ok for a few weeks, then needed to be thightened again. I complained to garage which measured the alternator output (at the battery end), replaced it and put in a new fan belt. Same story all over. What I now noticed is that the belt is unusually weard after a short while. The recomended fan belt has a flat bottom (a few mm wide) but the new belt is weard down to a V-shape after about 50 miles. There's got to be soemthing wrong here. My humble theory is that the replacement alternator drive wheel has the wrong inner width (profile). Where can I get the correct measures to prove this - or help to another possible solution. I had no proble before the replacement alternator came into the picture and I can live with a belt thats need changing/tightening every 2 - 3 weeks. Please HELP !

[More Power]

Use a straightedge to verify whether all of the pulleys line up correctly. A new alternator made for another application might not line up.

Next, have a look at the V-belt pulley mounted to the engine's crankshaft. GM used a rubber isolated crank pulley beginning in about 1985, which was designed to make life easier on the belt driven accessories. If the rubber elastomer in the crank pulley is cracked, missing pieces, too soft or otherwise not doing a good job, it'll be hard on belts and make it harder to keep them tight. Plus a damaged/defective crank pulley could cause harmonic induced crankshaft damage.

Jim

[Ratau]

I retrofitted a 120 amp Bosch alternator from a BMW onto my Blazer. It charge very good but eaten belts like crazy. Had to replace it every 1000 km. I found the 10 mm belt cant handle the torque so I changed the pulley on the alternator to a 12.7 mm. The 12.7 mm belt done 7000 km and no sign off wear yet.

[simon]

A new belt should be about flush with te top of the pulley groove and conform to the taper as well and have some clearance in the pulley bottom to fit properly. and all pulleys should line up with each other as was mentioned in other replys.
I thought that from 89 and up the flat serpentine belts where used. if that is the case count the grooves in the pulley on the alternator and see if the are the same as the crankpulley.

good luck

[Mr. Bone]

I've had this problem too. . . ulitmately what happened was the previous owner of my van used a different sized alternator( not the one made for the vehicle). Yeah, i supposed it worked in a pinch although over the long term it's a poor solution to getting the right alternator so the pulleys are properly lined up as mentioned in previous postings. So, you need to be sure this is the proper alt. I my case i went to an auto supply store and got the proper part to compare to the old one. all the best.

[FredM]

how do you determine the correct alternator casting? does it fit other GM models? because i have the same problem, the belt isn't lining up straight. i got an exchange from the rebuilders and had to drill out and file the lower mount to get it to go on.