I am using March Power and Amp crank and alt pulleys and I got the recommended size serp belt, which does fit. The tensioner looks like this:

.....|
\ |..........| | | /


The single | in the first line is where the indicator mark is. I had to use dots, as spaces didn't show up except on the write & edit post screen. Anyway, the belt tries to come off of the water pump pulley, the A/C pulley, and the pulley underneath it. The crank, alt, and power steering pulleys hold the belt just fine. (I don't think that will matter once one of the other pulleys throws the belt, lol.)

Within 5 minutes of starting the engine, the belt if halfway off of the water pump pulley (it comes off rearward, towards the engine).

Why is this happening and how do I keep the belt on the pulleys.

Thanks, and maybe it will be today that I finally drive the car!

 

Well, I started the car again and the belt was half way off the waterpump pulley within a minute. Also, the rearmost rib on the belt (the rib nearest the motor) separated from the belt. I'll go get another belt.

 

Sounds like either the crank or alternator pulley is misaligned... do you have a long straight-edge that you could check alignment against the other pullies with?

 

My 95 Chev truck did that. Found belt tensioner was worn out, and it's pulley was not aligned with the rest of the pulleys anymore. Had to be standing at just the right angle to see it.
Replaced tensioner assy, and all was aligned again.
Give the tensioner pulley a good tug and see if it will move towards radiator.

 

I checked the pully alignment and found that the alternator is pretty good, the water pump and tensioner pulley are right on, the tensioner pulley and the A/C may be right on or they may be off a little bit (that one was hard to determine, but I can't remeber why), and the A/C was good with whatever pulley is directly below it.

The crank pulley sticks out about 3/8" not enough. This would explain why the belt kept coming off the back of the pulleys.

I called March and talked to their tech guy, Randy. After listening to my description of the situation, he told me that it sounds like they sent me a truck pulley, which would be 3/8" less wide (from mounting surface to front edge of pulley where the ribs are). They are sending me the correct pulley with mailing labels to return the incorrect one.

Their customer service is really good, but I'm still mad because it's another two or three days that I have to wait to drive my car. (I don't have any air tools, so it's kind of a pain to have to drive somewhere to get the stock alt pulley put back on, run the car for two days and then go get the alt pulley switched back.)

I'll also check the tensioner to make sure it's not wobbling.

 

The alt pulley won't work with the normal crank pulley?

 

Nope. Sounds like the Power & Amp set that turns the alternator pulley faster to make up for the rest of the accessories turning slower so you don't have too low a voltage.

I wonder what would happen if you did leave it on and wound the engine up to 5000? (rubs chin)

 

I was going to ask about that (i.e. would speeding up the alternator with stock crank pulley and underdriven alt pulley mess up the alternator?), but then I realized that I didn't have the right length serpentine belt to try that setup anyway. I don't want to spend another $40 for a serp belt I'll use for two days.