'63 340 SHP alt./fan belt

[Jim C.]

At 5000 RPM my alternaton belt twists/flips over. Then it's trash. Any ideas why this happens? Belt tension seems adequate.

[Tom H.]

Re: '63 340 SHP alt./fan belt

I guess, first things first. Are your pulleys correct as far as you know ??

[Timothy B.]

Re: '63 340 SHP alt./fan belt

Jim,

If you have the deep groove pulleys, is it possible the belt is cut wrong and rolling on the pulleys, have you tried another belt?

Does your car have a idler installed?

[Jim C.]

Re: '63 340 SHP alt./fan belt

I guess, first things first. Are your pulleys correct as far as you know ??

As far as I know the pulleys are correct. It did top flight at the nationals a few years ago in Boston. I did have to add a lower pulley (making the total 3 pulleys ) when I decided to add power steering. (not an original option on a 63 SHP) . Pulleys seem visually to be in alignment , i.e. belts run vertically . The lower pulley closest to the block is vacant , the second is the alt. belt we're discussing and the outer is the power steering.( no problem with that one)

I do not know how to tell the difference between a "deep v pulley" and a non deep one. I have used a Quanta correct belt GM 3843162, 380x5500.
I have also tried a modern Gates which seemed a bit wide and rode in the top of the V. Hope this helps . I removed the idler pulley as that is where the PS pump is located.

[Domenic T.]

Re: '63 340 SHP alt./fan belt

I lost an engine that way and dove into the problem and found that the cooling fan blades were flexing at high RPM's and taking the belt off. They went back to their original shape att lower Rpm's. Back thene pulleys were a dime a dozen and I welded a thin strap to keep the blades from flexing out and that solved the problem.
The wrong sized pulley/fan was the problem.

DOM

[Domenic T.]

Re: '63 340 SHP alt./fan belt

I was trying to type and take a phone call at the same time and sent the post off with out finishing.
That was my problem as to why my belt was twisting and came off. I just had 1,000 miles on the engine and got it hot with new rings and that broke all the top rings. I put a new belt on and reved it up and it did the same thing. If it is the same situation I had the belt will have slices along the edge if the blades are hitting them.

DOM

[Jim C.]

Re: '63 340 SHP alt./fan belt

I was trying to type and take a phone call at the same time and sent the post off with out finishing.
That was my problem as to why my belt was twisting and came off. I just had 1,000 miles on the engine and got it hot with new rings and that broke all the top rings. I put a new belt on and reved it up and it did the same thing. If it is the same situation I had the belt will have slices along the edge if the blades are hitting them.

DOM

Thanks Dom, but the belt has no evidence of cuts or slices along it. I just drove over to Long Island Corvette and picked up a couple of new Quantas. Unless I get some other guidance I'll put some belt dressing on a new one and give it a try.
I was wondering if this was a common problem back in the day when these cars were new and possibly corrected in later years.

[Domenic T.]

Re: '63 340 SHP alt./fan belt

Jim,
For some one reading my posts, I was talking about the altinator cooling fan.
I can't really say it was a problem but I actually had blades fly off the generator cooling fan on my car while racing and dent the fender well and another time the hood.
I saw back plates behind the pulleys on some cars to prevent the altinator cooling fans from flexing back and hitting the belt. I also saw a fan/pulley combo at a swap meet that had something behind the pulley (back plate)that prevented fan flex, the guy said it was off a corvette but I didn't know what year he was talking about. I changed the pulley diameter on my vette back then to turn the altinator at a slower speed and was happy. I am doing a frame up now and am ordering the correct pulley from LIcorvette. I found the correct fan but my pulley is still wrong.

DOM

[Stuart F.]

Re: '63 340 SHP alt./fan belt

It is important to be using the correct pulley and fan on the alternator. It is bigger in diameter and is deep grooved for use on the SHP engines. I have had mine since new and never had a problem with it except for Chicago Corvette tried to steal it (whole nuther story). The basic arrangement on the 340 hp is a two groove crank pulley; one belt driving the alternator, water pump/fan, and the other belt also driving the water pump/fan and tensioned by the idler pulley. The obvious intent was to make certain the water pump and cooling fan were being driven even if the alternator belt flew off at high RPM's in order to save the engine.

GM learned their lesson specially from the early Pontiac HP engines with a single belt driving the pump and alternator. They used a reverse cooling system that depended greatly on the water pump working at all times as you did not have a natural water flow (heat rising, etc.), rather they pumped the coolant into the heads first forcing it down into the block later. If you lost your belt, as many a 59 389 ci did, you'd get instant overheat and great potential for engine damage. Many folks stuck in solid lifter cams that would allow the engine to rev way beyond the design of the alternator, pump and fan belt system. Heck, even the hydraulic lifter stock units would do that as many people found out. I beat a lot of those buggers because they lost their belts.

Stu Fox

[Stuart F.]

Re: '63 340 SHP alt./fan belt

The story I was eluding to about the attempted theft of my alternator pulley is just that. Anyone who sends their alternator into a vendor for rebuild better check which pulley they get back with it. The bad guys know the SHP pulley is worth money and hard to get, so they will attempt to pass off a standard pulley. This may or may not be your problem.

Stu Fox

[Duke W.]

Re: '63 340 SHP alt./fan belt

Pulley alignment is a common issue. The 340/360 HP coolant pumps had the pulley mounting flange at a different axial location on the shaft. A 250/300 HP pump will not have the flange at the right location, which will result in pulley misalignment.

Duke

[Jim C.]

Re: '63 340 SHP alt./fan belt

Pulley alignment is a common issue. The 340/360 HP coolant pumps had the pulley mounting flange at a different axial location on the shaft. A 250/300 HP pump will not have the flange at the right location, which will result in pulley misalignment.

Duke

If misaligned, would one notice the misalignment or would it be so minor as to not be perceptable?
In my case I am not able to detect misalignment visually. I did have to "stack 3 pulleys" which came with the P/S conversion kit. The P/S pump rides on the outer crank pulley and the alternator/water pump on the middle crank pulley. The inner crank pulley is now vacant. Any other location for these belts creates a very obvious misalignment.

Were 63 SHP engines prone to twisting fan belts at 6000 rpms?

PS I just bought a new Quanta belt , perhaps the the age of the previous belt was an issue as well. Maybe it's telling me runs to redline are not such a good idea? But it's soooooo much fun to hear that solid lifter engine.

[Clem Z.]

Re: '63 340 SHP alt./fan belt

At 5000 RPM my alternaton belt twists/flips over. Then it's trash. Any ideas why this happens? Belt tension seems adequate.

buy a wrapped belt not a cut belt. ag belts are the best you can buy. back in the day we used corvair belts because the were the cats nuts when it come to staying on the pulleys at speed. now if we wanted more HP like at the flying mile on daytona beach time trials we cut the belt part way thru so it would break and come off freeing up HP.

[Stuart F.]

Re: '63 340 SHP alt./fan belt

Clem;

Bet you didn't do that with a reverse cooling Pontiac, did you?

I still suspect the alternator pulley because many an SHP 63 had theirs stolen or misappropriated and replaced by a standard L-75 piece.

Stu Fox

[Clem Z.]

Re: '63 340 SHP alt./fan belt

a pulley alignment checking tool can be made from a piece of straight 1/4" diameter steel rod. get a piece about 18" long and bend a 90 degree bend in one end about 6" from the end. lay the 90 degree bend into the water pump pulley and face the other end towards the alt pulley and then the crank pulley. the rod should hit on the middle of the other pulleys if all is in line.