Originally Posted by
rodekyll
I mean that the pulley halves (shivs) are not spinning on the same center and in the same plane as the alternator shaft. The most common reason is that the two shivs (pulley halves) are misaligned -- either the big tab/little tab in the wrong holes, a shim slipped keeping the shivs from mating, one shive is warped, the alternator shaft is bent, or that 'bell' washer that goes directly behind the pulley nut slipped. Any of the above will result in the belt running deeper (looser) at one point of rotation and higher (tighter) at some other point. Of course that's going to ruin the rotational balance and cause a harmonic vibration. It can also get the fan thrashing and scraping on the edges of doghouse stuff.
This can happen with the alternator otherwise feeling 'normal' when the belt is removed, since it's the relationship of the belt to the pulleys that's the problem in my WAG scenario. The trick is to watch the pulleys go 'round at low (starter) speeds (belt installed) to see if you can eyeball the wobble. Once you can see it you can kill it.
Yes, you can get you hand in the big doghouse hole if you get the alternator and flange out. Depending on what-all you've got going on back there equipment-wise that could be much easier said than done. The doghouse might need to be unbolted and lifted to clear the alternator pedestal. If you have the heat flaps installed you have to pull the thermostats bellows and linkage to lift the shroud. The throttle cable can get bound and kinked whenever you tinker with the shroud. So be careful with it! Different carb/injection setups can make removing the intake and other things necessary, too. So I wouldn't pull the alternator until I was convinced that I had to. Checking the pulley stuff has a high enough percentage that I'd try that first.
Another way to check for loose baffles is to tap the doghouse here and there and listen for the loose panel to reveal itself. Quite often you can hear or feel the troublemaker flap as you tap.
That's all I've got right now. I'm working on a superbeetle right now. Engine is out and (oem) fan shroud is removed. If you need me to look at anything in the unseeable behinds of the engine, let me know. It goes back together thurs/fri.