[JUDGE3]

I know theres had to be plenty of others seen this condition. didn't know where else to post this.
My 69 gto has the factory v belt pulley(s) set up. once I put my new higher performance engine in the alternator pully squeels like no tommorow over 3,000 rpm. tried different belts, shims here and there to try an overcome what i'm guessing is "torquing" of the alternator itself under load. is there an alternator pully out there to cure this? or is the only cure the march serpentine belt set up? quick pic of my new motor

[BobDef1]

try march deep groove pulleys

[ta man]

Are your pulleys painted?

[Mike S]

I tried that big Moroso alt. pully. Save your money, it didn't charge till 3000rpm. I ended up with a deep groove pully a little larger than the factory one. I took the factory pully to a local drive and bearing shop and they hooked my up. It was made for a little wider belt but has the same taper. bad side is I have to get it to 2000rpm to start chargeing but once it starts chargeing it will charge at idle.

['ol Pinion head]

Chevy used a special deep groove alt pulley on their '837 37amp alt. (Z-28 & rect port Chevy alt...very expensive). Same pulley has been found on numerous industrial usage Delco alts.

This factory deep groove alt pulley is also reproduced. Might ck Rick's First Gen Camaro or eBay.

[mysticmissle]

Making sure everything is perfectly aligned, ie within a 1/16" or less, keep belt as short as possible with alt relocation if necessary, the moroso alt pulley solved my belt issue. I have used it w factory bottom pulley and aerospace mandrel. Are you driving water pump too? Extra length is ur enemy at high rpm
Just reread ur post. With factory drive set up nd no elec pump you propably will need march or ram air net deep pulleys at any sustained high rpm. How high do u spin it ?

[Half-Inch Stud]

I'm convinced that Vee-blet success starts with compatible Vee-Belt & Pulley V-sizes.

Pulleys do wear out, so be sure to inspect the belt is loading on the Pulley sidewall Vs, and not bottomed-out on the pulley floor.

[66bonne]

I agree with half-inch stud about belt size must be correct.
http://www.cvfracing.com/
I had a belt throwing problem on my 455 until I put the CVF racing pulleys on. No problems since.

Jim

[1978 T/A]

I have not thrown a pulley with the stock pulleys. But I have noticed a screech when I snap the throttle quickly at a low RPM. Don't notice any kind of noise about 3K though. Subscribed for a quick fix!

[Skip Fix]

RARE has some nice deep groove pulleys for crank,WP and alt. Have them on my pump gas and IA motor.

I had a screeching I couldn't get around on the 81 car until we swapped out the clutch fan, it was too locked up all the time.

[1qikta]

Originally Posted by Skip Fix

RARE has some nice deep groove pulleys for crank,WP and alt. Have them on my pump gas and IA motor.

I had a screeching I couldn't get around on the 81 car until we swapped out the clutch fan, it was too locked up all the time.

I went to the RARE deep alum pulleys after belts were rolling above 6000 rpms. No issues since...and they look stock. Just scuff and paint to match

[lust4speed]

Check the hole in the bracket that the bolt for the alternator goes through. If it doesn't fit the bolt tightly, the alternator will pitch in towards the crank pulley under load. I'd also remove all the paint on the belt contact surface of all the pulleys.

As far as checking belt alignment, we've tried straight edges, lasers, and other attempts at determining whether the pulleys were actually in line. Best tool we have found is a straight length of 3/8" tubing (gas line or whatever) about three feet long, because it self aligns in the pulley grooves. Basically push it into place on the crank pulley, and then simply move it down into position on the alternator pulley groove. If it hits one side of the groove or the other, you have found your alignment problem.

[60man]

Originally Posted by Half-Inch Stud

I'm convinced that Vee-blet success starts with compatible Vee-Belt & Pulley V-sizes.

Pulleys do wear out, so be sure to inspect the belt is loading on the Pulley sidewall Vs, and not bottomed-out on the pulley floor.

Agreed HIS....when I started spinning my motor over 6K I went with a larger alt. pulley...a ebay one for a tractor 3.5" deep grouve.. IIR.. Worked fine. When I went with vac pump I used stock crank pulley with Aero mandrel thinking aero pulley was too small..It started zinging belts..It was just a "tad" out of alignment..I had omitted rhe stock spacer behind the pulley....duh..I removed the stock crank pulley and went with Aero belt grouve WITH the stock spacer...presto no zinging belts..
Long story short...alignment is critical at speed...Pontiac used some factory spacers/shims behind crank pulley.it may have been used as a reinforcement for mounting bolts as well.....otherwise the belts try to "climb the wall" of pulley.
I'm finished ..

[Pontirag]

check corvette vendors. price is relative. If you only pay once and it works. its important to have all the factory brackets. Lots of times I see alternators missing the rear bracket. Engineers thought it was important.

[BruceWilkie]

Originally Posted by Pontirag

check corvette vendors. price is relative. If you only pay once and it works. its important to have all the factory brackets. Lots of times I see alternators missing the rear bracket. Engineers thought it was important.

Yep! You ever see how elaborate the accessory bracketry was on the Buick V6's?

Even when things are very well aligned the belt itself has a tendency to show a harmonic to it as rpm increases. Pulley balance, water pump/accessory balance and the belt balance itself, can and usually are less than perfect plus as you mentioned bracket deflection. (BTW you may or may not be able to hear any belt squeal but you can almost always see belt flex, espeacially on long spans as rpm increases.)

A solution to belt tossing that has worked quite well for me..........
I have made belt "retainers" that basically were an oilite bushing on an axle(bolt) just about touching the belt, mounted just before the pulley entrance.(closer to pulley entrance the better)You may need to make a braket to mount this. Quite effective as you could see a shine on the bushing after a pass but never lost a belt after this mod. Definately stopped the belt from being able to climb out.(and no new pulleys were needed) It doesnt fix the true cause but it does stop the belt toss very well.

If your belt only squeals when you rev fast in neutral but never in normal use or rapid accell/decell in gear, DONT tighten the belt more. You'll put excess load on crank and accessory bearings. Chances are this type squeal is from insufficient belt traction due to either a substitute component or not enough belt "wrap" on a pulley due to component placement or wrong belt length. Too long or too short can affect how much pulley the belt actually contacts.



fwiw... I figured out my belt retention mod way back in the early 70's when I had my Corvair Spyder. Corvairs were notorious for belt retention problems due to the "vacuum cleaner" style belt routing arrangement they used.

[Tom Vaught]

Originally Posted by BruceWilkie

A solution to belt tossing that has worked quite well for me..........
I have made belt "retainers" that basically were an oilite bushing on an axle(bolt) just about touching the belt, mounted just before the pulley entrance.(closer to pulley entrance the better)You may need to make a braket to mount this. Quite effective as you could see a shine on the bushing after a pass but never lost a belt after this mod. Definately stopped the belt from being able to climb out.(and no new pulleys were needed) It doesnt fix the true cause but it does stop the belt toss very well.

fwiw... I figured out my belt retention mod way back in the early 70's when I had my Corvair Spyder. Corvairs were notorious for belt retention problems due to the "vacuum cleaner" style belt routing arrangement they used.

Very common to have a 'idler' before the entrance on a supercharger pulley.
Does a couple of things: Allows more belt wrap which improves "clamp" on the pulley and it keep air from getting under the belt before it gets to the pulley eliminating a lot of the "slip potential".

Agree Bruce, it works very well without having to reef on the alternator to get a super tight belt wrap and possibly kill the alternator bearing.

Tom Vaught

[Gach]

Here's what worked for me, I used a 1970 GTO alternator bracket, got rid of the Moroso 5 inch diameter, deep grove pully and put a 3 inch diameter Deep grove Pulley on the alternator, which allows it to charge a 1500 RPMs. The 70 alternator bracket allows for real short alternator belt, which is one of the biggest problems with throwing belts. The crank pulley I use a big block Chevy deep grove aluminum pully about 6 inches in diameter. From the summit. For the alternator I had someone make me up a 3" diameter aluminum deep groove pully to match the big block Chevy pully. It's a high HP high torque motor that gets buzz to 72 to 7500 RPM and have never lost or had a squealing belt since. I have no problem keeping a battery charged either.

[Half-Inch Stud]

...I haven't used the rear Alternator Bracket in 28 years. They sell real good.

Reason: I don't like the opportunity of the Water Pump Neck gasket getting scrubbed silly by Alternator vibrations.

[Pontirag]

I'm betting the engineers thought about that.

while the alternator will inevitably vibrate. if you install the rear bracket it wont move anywhere near enough to cause harm to a housing gasket. at least not in the million plus cars they made with it. Like I pointed out in other threads, I have seen a 75 Grande Ville lifted completly off the ground by the alternator brackets. so they are pretty strong.

[rkm1003]

I went to the RARE deep alum pulleys after belts were rolling above 6000 rpms. No issues since...and they look stock. Just scuff and paint to match

X2.........was slingin belts every pass at 5000, RARE pulleys on, not one belt lost since at 6000+.