Alternator/water pump belt keep burning off

[DMCMW Dave]

I had a similar issue many years ago. The water pump pulley is the press on type and had started to back off the shaft. The shaft has an internal thread, i used a long socket and a bolt to press it back on, then had a spacer machined up to keep on there permanently to keep it from backing off again.

This can happen if the pulley is re-used more than once. Eventually it's too loose on the pump shaft and will walk off.

[mr_maxime]

Dave, what is the proper spacer for the DMCH alternator. PO owner used a nut but when I grabbed some calipers, I had 0.42" of space and the washer was slighter thicker. I grabbed a 10mm nylon spacer (. 42" is slightly larger) from ace to replace it temporarily.

I also had lots of broken belts and I think that oversized spacer had something to do with it.

[DMCMW Dave]

Dave, what is the proper spacer for the DMCH alternator. PO owner used a nut but when I grabbed some calipers, I had 0.42" of space and the washer was slighter thicker. I grabbed a 10mm nylon spacer (. 42" is slightly larger) from ace to replace it temporarily.
.

Normally there isn't one, there is a sliding bushing on the alternator. the fan-end bracket on the alternator should be right up against the cast bracket. BUT if someone has modified the bracket to make some other unit fit, all bets are off!

[David T]

The bracket holding the alternator also can be adjusted fore-and-aft. If you have changed the alternator it could have the wrong pulley for the belt. Or you could be using the wrong size belt. If you over-tighten the belt you can break the cords inside the belt and then it rolls over or flies off. First step is to make sure all of the pulleys are in the same plane. Next would be to make sure you have the correct belt and each pulley is correct for the belt. You also must check that all of the bearings are OK. If the bearings in the water pump or alternator are going bad it can cause the belt to come off. If you have spacers on the alternator, the better, cleaner way to do it is to reposition the pulley on the alternator so you don't need to adjust the alternator. The crankshaft pulley sets the plane, the water pump pulley must be aligned with the crank pulley and then the alternator pulley must align with the crank and water pump. Use a laser or a string to check the pulleys. A Vee belt must NEVER ride on the bottom of the vee, it must contact each pulley ONLY by it's sides. If the bottom of the belt touches the bottom of the pulley's vee you either have the wrong belt or the wrong pulley. If the belt is shiny on it's sides, it is slipping, that means it is too loose, a bearing is bad or it is riding on it's bottom. If a pulley is rusty or bent it can throw belts so carefully check each pulley.