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Discussion Starter #1
just got my car so I'm dealing with someone elses handiwork. When I rev the engine up it throws the belt that runs the alternator and water pump. The pulleys for the crank, water pump and power steering all seem to line up fine. The alternator seems to be a little off though. It has all OEM pulleys and brackets. Except the alternator has been changed to a polished aftermarket unit. It has the correct BB alternator brackets and spacer on it. Is there specific alternators just for big block cars? At this point I just don't feel safe driving the car until I can keep it from throwing the belt.
 

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I'm sure that someone with real knowledge will answer but I believe that the big block cars came with deep grove pulleys to prevent this problem. Perhaps you simply need a new pulley for your alternator.
 

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I used the same alternator that was on my small block on my big block, so I would say the alternators are universal. I ordered big block brackets which are not the same part as small block. It’s the brackets that are different.I’ve got a shelf full of original pulleys. Replaced with deep groove aluminium pulleys. It’s probably more luck than anything else that they have always lined up perfectly (with a little manicure to make the mounting holes slotted for fit on my 454).

The slightest misalignment, even with deep groove pulleys, will toss a belt at higher rpm.
 

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Aftermarket heads???

On this small block Nova and my last one with AFR heads I had to take about an 1/8" maybe a little less off of my alternator aftermarket spacer. Two different brands of alternator brackets/spacers and both on different sets of heads. Anyways ran last car to 7000 rpms and this one 7000+ and belt always stays on.

Line up a straight edge, string or laser with top of inside grooves and see what's going on.
 

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Line up a straight edge, string or laser with top of inside grooves and see what's going on.
That ^^^

Alternator alignment issues are usually much easier to correct. I've been there myself. But...

I fought the power steering pump causing belt issues on my small block for many months (over a year, actually).
I went through every bracket and spacer I could get my hands on. Some were clearly misaligning things. Others looked like they were correct. Shims, washers, and mixing-and-matching got me nowhere.

I even tried a new pump and half a dozen different pulleys on the pump. It never worked.
I drove the car for about 9 months with the power steering belt removed. Life was better fighting a power steering box without hydraulic pressure, than fighting the belt.

I was so frustrated that I actually bought a complete manual steering setup out of a parts car from another member here (from the rag joint to the tie rod ends).

Just before I was set to install the manual steering box, I gave it one more chance. I pulled the fan, shroud, and upper radiator hose, so there was nothing in my way, and put a 24" straight edge on all of the pulleys.

I discovered that eyeballing the pulleys did have them quite close, but the power steering pump was still at an angle.
The bigger discovery, however, was that my crank pulley was bent - in two different ways. It was off-axis, and also had a bent lip. Every time I had eyeballed the alignment, I was working with a crank pulley that was sitting at a different angle, even though it looked okay. (Never saw it with the engine running, either.)

Careful use of a jack and blocks, as well as a slight adjuster massaged the crank pulley back into position. (This pulley is a V-groove / multi-groove 'hybrid' and I couldn't find a replacement. Otherwise, I would have just replaced it. A member did donate another similar crank pulley to me, but the spacing was incorrect.)

One of the aftermarket bracket sets that I had first bought during that ordeal required just one additional washer on each bolt for perfect alignment. Some thread locker on the bolts locked it down after a few months of use showed that it was finally good to go.

That was two, maybe two and a half years ago. All I've had to do since then was adjust the belt ... because it finally got enough use to stretch.
 

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I had this exact issue with my small block a while back. Every time the car spun over 4,000RPM, it would fling the belt. Turns out I had the wrong alternator bracket, with poor spacing, and a lower bracket was bent- it was about 1/4" off.

I used a 90* straight edge and a laser level to get it dialed back in, and after that, no more flung belts.

 

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All the alternators are the same.

Get a pen style laser pointer which you can lay in the groove for the pulley, to check alignment. The laser should be in the center of the groove for whichever pulley you are checking alignment on. Make sure the crank pulley has no spacers behind it. Check it's groove alignment compared to the alternator pulley groove. Then compare it to the water pump pulley groove.

If needed, you can buy proper spacers for behind the water pump pulley, and to shim the alternator pulley, can buy machine shims in different thicknesses.

Be sure the brackets for the alternator are not bent.

Using the proper belt is also important, the top of the belt should sit flush with the top of the pulley. I have fund NAPA Premium XL belts are the best. 15/32" wide.

For example I use a 25-7570 on my BBC with short waterpump and the march pulleys/brackets. The alternator is outboard on the drivers side. I have seen over 6500 rpm many times and never thrown a belt.
 

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Discussion Starter #8
Well, tried a few different things, never could figure out exactly what the root cause was. So....I ordered a set of new pulley's from march, and a new alternator. Why stop there I thought:D, I ordered the correct BB radiator and shroud, mechanical fan, and Hi Volume aluminum water pump (Radiator is from Cold Case, shroud is OEM, Fan is a 18" flex 7 blade)Also got correct hoses and Misc. Also found a few wiring gremlins:devil: as I was removing stuff, going to address that too.
 

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I used the March 2 groove pulley set on my race car for many years with an Edelbrock victor aluminum pump. I put the one belt around the crank, pump and alternator and a single belt from crank to water pump. Never lost a belt ever on that car. Shifted at 7500 and crossed at 7600. Went 9.30's at 141 with it. Only swapped to an electric so I could cool the car between rounds better.
 
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