This is rather peculiar. I would think that an alt bearing that was bad enough to seize would seem pretty screwed up when you spun it by hand. IIRC, the alt belt touches only the alt, the water pump pulley, and the crank pulley. Is that correct? Does the water pump spin freely by hand?



How the heck tight are you getting it? I think a finger pushing on the belt midway between the alt and the crank should be able to deflect the belt at least 1/2" without really trying. Tighter than that is probably too tight. Getting the belt tighter than necessary to keep it from slipping just puts additional stress on the alt and water pump bearings (and the belt itself).

 

The alternator belt runs on the water pump pulley and main engine pulley. If the water pump was your problem you would also be having a problem with the air pump belt as well since they both run on that pulley. The alternator is the only thing that makes any sense that could be cauing it. Alternator bearing is about 20.00 at rockauto.com and a new alternator is 122.00 with a 60.00 dollar core. try to tighten the belt with about 1 to 2 inches of deflection.

 

Thanks for all the advice people. I fitted a new one (a wee bit less tight) and drove 75 miles with no probs