It seems a lot of people are having problems with generator pulleys exploding. In some cases, the cause of this is not having the correct number of shims. You must have a total of at least 8 shims. If you do not have the correct number of shims, the bell will not tighten on the outer half of the pulley, which will allow the pulley to stay loose. In other words, the inner diameter of the bell bottoms out on the shoulder of the rear half of the pulley. This leaves the two pulley halves loose. They will work against each other causing them to explode, not to mention, it ruins the key way slot on the generator/alternator shaft itself. Many people tell me “mine is fine and I only used 4 shims” Not true. The belt is holding the halves apart, giving the illusion that it’s tight. So make sure you use 8 shims. What you don’t use between the halves, use under the bell. If you’ve already thrown a pulley, putting 8 shims on after the fact may not cure your problem. In most cases you have wallowed out the key way slot on the generator/alternator shaft and/or ruined the spacer that’s on the shaft. The only fix is to replace the generator/alternator.
Ok you’ve done all the above and you’re still having problems with the pulleys. This is a common problem these days. I will explain what to look for, and then you can check yours. When buying a new one, check it before you hand down cash. Let’s look at the generator/alternator without the pulley. What you should see is a shaft that comes out for the pulley but more important is the spacer that the pulley sits against on that shaft. Take note; It’s flat or it was flat. The inner part of the pulley sits on that flat spacer. When the pulley is tight it is up against that spacer. We want the pulley to sit flat on that spacer, so we have full contact of the width of the spacer. Lost? It will make sense in a minute.
Grab your pulley. If it’s on the car it might be easier to take it off. Look at the area of the pulley that hits that spacer. Is it flat? Most of you are going to say no. Here in lies the problem. It should be flat or at the very least have an ever so slight bevel to help you get it started on the shaft. What I see with a lot of pulleys is a large counter sink. When I say large I mean it’s as large as the width of the spacer. Ok so what? Well now instead of having a contact area of .100 thousands (the width of the spacer) we might only have .005. Again so what? Well what happens is the pulley starts wearing out the spacer, and then the nut is loose. So you tighten the nut again and the spacer wears more. In between your tightening, the pulley is loose and is wearing on the keyway. Not to mention the whole time the pulley is getting closer and closer to the body of the generator/alternator. I have seen most generators/alternators have spacers that are no longer flat but beveled. You can’t just buy a new spacer. You get to buy a new generator/alternator. Have you ever seen a pulley hit the body of an alternator? My guess is yes. Well that is usually the reason. Wouldn’t it be nice if we could just start with a good pulley? Don’t think that if you just bought a new German one that it will be good. Take a look at the back side. If you see a large bevel it won’t last any longer than a cheap China pulley. I am finding now the pulley that is working best for me is a Billet pulley. It’s not cheap but it is hella cheaper than a new generator/alternator.
What about belts? Well I like the continental belts. Most times you would use a 9.5 by 905. That belt is narrower than your American belts. That means less shims between the halves. I have had the best luck with the continental belts.
How tight should the belt be? That’s a fine line. Too tight and you will wear out the bearings in the generator/alternator; Too loose and the belt will slip. A general rule I use is ½ deflection. In other words, if you put a straight edge on the belt from pulley to pulley you should be able to squeeze the belt in the middle and you should see approximately a ½inch gap between your straight edge and the belt. Again that is what works for me.
So what have we come away with from this? 1) You need to have 8 shims minimum. 2) Most of the new pulleys are not made right, even the German ones. 3) Are there any good pulleys out there? Yes, you just have to know what to look for.