Ok, I'll be right up front here and admit that this question is to help me finish the rebuild on my daughters Blazer but you guys are the greatest when it comes to helping people (and I could just as easily be putting this motor in my GT (*S*).

The problem is that the serp belt keeps working off the back of the crank pulley as soon as the motor is started. It hops the ridge and tears up. The motor is an 95 4.3 vortec with air.

Anyone have a fix?

Thanks

Make sure You have the right belt, also a worn belt tensioner or locked pulley can break the belt or cause the belt to jump off. BOL

Jim

When the belt is off do all of the pulleys turn easily -except the crank of course. After the belt is on, if you look strait down the belt, do all of the pulleys line up - none stick out or look crooked?

quote Originally posted by Ken_86gt: ...do all of the pulleys line up - none stick out or look crooked?

This was my thought, too.
Harmonic balancers sometimes can be a real bear to get "seated" properly.
If it wasn't pulled down all the way, it would leave the pulley sticking out towards the front. The natural inclination would be for the belt to "walk off" the back.

quote Originally posted by Ken_86gt: When the belt is off do all of the pulleys turn easily -except the crank of course. After the belt is on, if you look strait down the belt, do all of the pulleys line up - none stick out or look crooked?

Yes, a good straight edge is the way to go here. Rotate the pulleys to make sure that they spin true and double check them against the other pulleys with the straight edge. Belts that jump a notch or two usually means that something is mis-aligned or the grooves of the pulleys have a build up of gunk which would require a good cleaning. Purple Power and a nylon scrub brush followed by a rinse of brake cleaner will do the trick. Belts that have jumped a notch or two may be prone to doing that again, sometimes it's wear or a manufacturing defect, try a different belt.

Your symptoms are classic for a belt which does not have the same number of ribs as one of the pulleys on which it rides. Check all pulleys to make sure their grooves match the belt. Otherwise, check for an out-of-plane pulley as previously mentioned.

Paul McKibben
Norcross, GA