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Discussion Starter #1
I am throwing alternator belts at RPMs above 5K. it is much worse in first gear than in higher gears. If I take it easy the belt will invert instead of come off. I have a 406 small block in a 79 Z28 at about 500 HP. I have replaced the crank pulley, alternator and all three of it's brackets. It is head mounted. Pulley alignment looks fair, not perfect. The alternator looks like it is a bit forward from the water pump pulley. I have tried all combinations of washers behind the alternator adjusting bolt. The straighter I get it the worse it throws belts. I put a spacer behind the water pump pulley, which made both the alternator and power steering look perfect and started throwing the power steering belt as well, so I took it out. It appears that some misalignment is required for the power steering belt to stay on. I really do not want to go out and buy a serpentine arrangement. Has anyone got any ideas?
 

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Chris,

I'm just going to throw this out there, but make sure you have matching crank and water pump pulleys. i.e. later model SBC have a crank pulley with one large OD groove and two smaller OD grooves. The water pump pulley must have one large and one small OD grooves. Check this to make sure. I've seen people throw belts from putting a water pump pulley with both grooves the same OD on a crank pulley with different OD grooves. Just something to check. Take care.

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69 SSRS Frame-off Resto
81 Z-28 377ci Drag Car
 

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I had this problem a few years ago and switched to a different brand of belt. I cannot run the NAPA belts. They come off after a few miles. I can , however, run a Goodyear or Mercruiser (gates?) belt without a problem.

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Mark
1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
 

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Discussion Starter #4
I should have mentioned that the pulleys are correct. The crank pulley is a three groove, 7.75". The smaller groove is for power steering. The water pump is a two groove. The smaller groove is also for power steering. The air conditioning and air pump are gone. A goodyear belt does stay on a little better, but one pass in first gear will throw it too. I have also tried a deep groove pulley on the alternator with no success. I am about to try a 5" alternator pulley with a 17/32" belt, when it comes in. Up till now I have been using the 15/32" factory size belt. I am still a bit perplexed as to why the power steering has to be slightly OUT of alignment (As it came from the factory) to stay on.
 

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Discussion Starter #6
The alternator is mounted to the head on the passenger's side in the factory location with one long 9/16" bolt. I have changed out the upper bracket to a single point mount BP bracket screwed to the water pump. This was my first shot in the dark. I have also changed the heads to Dart's, but had the belt problem before with the stock 400 heads. With a 44.5" factory size belt, I do have to run a washer between the top bracket and the alternator or when I tighten the top bolt it pulls the alternator too far forward. I have also noticed that as the alternator swings through it's adjustment range that the distance from the top bolt hole to the top bracket gets wider at the inward end and does not actually contact the bracket until it is about 75% of the way toward it's outer most position. Is there more than one long water pump? This is about the only thing I have not changed out.
 

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Go with a serpentine setup and cure all your headaches.
 

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put a set of underdrive pulley's on it they won't affect the amp's or steering that much. and if you slow down your water flow it will cool better.
 

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If it were me, I would not start buying expensive parts which may not be necessary until the problem is fully understood. While a serpentine belt system IS a slick way to go, normally a bone stock alternator belt should not slip off (assuming it is the correct belt) no matter which brand it is.

Years ago I had heard somewhere that belts are thrown more often if the alternator is on the driver's side of the engine. While I do not fully understand why this is, or if it is even true, I just had to ask.

You say that the belt throws most often when you're in first gear. Obviously, your engine can rev much faster in first. Before the belt is thrown, can you hear the belt slipping at all? Have you had someone watch the belt if you (briefly, in neutral!) rap the throttle? Could you have an excessive load on the alternator which may cause it to be driven less easily? You may want to try removing all electrical connections to the alternator and see how that impacts the problem.

It sounds like you have taken the time, and some money, to make sure you have the correct components. (FYI, the OD of my alternator pulley is 2 7/8", the belt is 3/8", and the distance from the alternator axis to the water pump axis is 8 1/8".) Try disconnecting the electrical connections first, and if that doesn't help we'll think of some other experiments to try.



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http://www.geocities.com/dmdirks/Automotive.html
 

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go to a junk yard, get a serpentine pulley set up off of a 85-86 chevy truck. it has a serpentine drive for the alternator and v-belt drive for the ps pump. i used this with a march performance alternator bracket and it worked perfectly. i paid $25.00 for the pulleys. no more thrown belts here. the pullys have a narrow serpentine with double v-belt for power steering.

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67 RS
355, SUPER T10 4 SPD
9" FORD
 

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From my personal experence... I put a gator back on my power steering and had it twist (turn inside out) after some high revs. Then it came off every time I straightened it out and put it back on! After the 3rd time without getting out of the garage I took a good look at it. It was real distorted almost square on one side like this -> \_| instead of the way it should be -> \_/

I put a gates belt on and the problem went away. The thing I noticed about the 2 different belts was the way the belts were ribbed. The gates belt is straight -> | || || | and the gator back are at an angle -> //////

I think the angle cut caused the belt to roll because the pullies are just the slightest bit out of alignment. The straight cut seem to tolerate this and don't twist or throw.

Recomendation: If a belt twists (turns inside out) it's shot and should be replaced. Like mine your pullies might be just a little mis-aligned. Try a gates belt or any other with the straight ribs. If it still throws it Look for a mis-alignment or a bent pully...

For the record I pulled the belt to look for wear after a few weeks. Nothing abnormal, the mis-alignment is ever so slight it only effected the gator back.

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...Dennis
Topless'69
Camaros Limited Nor-Cal
[email protected]
 

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You have to have all pullies lined up perfectly with each other in order to keep your belts on. It seems to me from reading your post that you have a probelem with your alternater placement. Don't change the water pump pully placement, change the altenater placement. I dosen't mater if you run a V-Belt of serpentine setup, pullies have to be perfectly in line.
 

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I had the same problem on a 77 Camaro I owned years ago. The car had 4.10 gears and a healthy solid cam that would rev to 7000 rpm very quickly. It turned out that the cooling blades on the cheapo rebuilt alternator that I had on the car were so thin that they flexed far enough at high rpm to touch the belt. I put the big Moroso alt pulley that covered the fins and the problem went away. I figured it out by watching the alt as a friend revved the engine as RacerX suggested.
Stephen

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67 RS/SS 350 700R4
69 SS clone unfinished
72 454 Weekend Racer
 

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Discussion Starter #15
Thanks for all the suggestions. This was exactly what I was looking for when I decided to post here. Lets see if I can address all these items. The serpentine idea from the junk yard is a good one. If all else fails I will try this, however the first junk yard I called will not sell the pulleys off of any of their engines, they want to keep them complete. I have already tried watching the belt while revving in neutral and all looks great. It has to be under floor board operating conditions for the belt to go. I do know that after a belt rolls over it is junk as one side is stretched more than the other. No I do not ever hear belt slippage squeal and I keep it pretty tight. DjD, I am curious, what is a gator back belt. Is this a type of belt? So far I have been using Kelly Springfield and Goodyear. Using a straight edge and a 5" alternator pulley, I have discovered some minor misalignment. The alternator is tilted in farther on the side toward the water pump. There appears to be two reasons. First is the obvious, belt tension pulling it that way. Second is the amount of slop between the bottom alternator bracket and the 9/16" bolt that goes through it and into the head. Tomorrow I will try sleeving this bracket's hole to take up the slop and will also put washers between the bottom face plate bracket and the water pump.
 

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Chris - gater back is a goodyear belt. Around here it's what your handed when you ask for a belt at most parts stores. I had to go to a corvette speciality shop to get a gates belt. The guy behind the counter said he wouldn't carry anything but gates... By the way my alt belt is a goodyear and hasn't given me any problems yet. I have a spare gates in the trunk just in case...

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...Dennis
Topless'69
Camaros Limited Nor-Cal
[email protected]
 

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If you decide to go serpintine, give Trans Am Creations a call. They sell a complete (used) system. They work great. They basically give you the front of the motor, including the w/p, p/s and a/c compressor. Their number is 305-769-0985. They also have a ton of 3rd and 4th gen parts. Great place to deal with, and NO, I don't work there.


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Mark
1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
 

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Gates belts are tops - have used them for years on every motor you can imagine, never had any kind of problem with them. Pulleys do have to be reasonably well aligned - work on your alternator mounting, not crank or water pump.

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JohnZ
'69 Z28 Fathom Green
 

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Discussion Starter #19
I thought I had things lined up pretty good, put on a 5" alternator pulley and new belts. By third gear both belts came off. I tore the whole thing down and using a steel square noticed that the water pump pulley and crank pulley grove centers did not line up. I had to put 1/8" behind the water pump pulley to get them to line up. I have replaced both of these pulleys with other stock ones and compared to see if there was any differences from old to new and there was not.

Someone mentioned crank shaft end play. How would I tell if I had a problem here? I pulled on the crank pulley and could not move anything. I tried prying behind the balancer, and also could not move anything, but my leverage was poor. I scribed a line on the balancer so I could watch for changes in position relative to the timing plate and can not see any when revving. This weekend I will have a friend brake torque and look for movement again.

Why would a stock crank, balancer, water pump and pulleys not line right up when bolted on? It seems odd that any spacing behind the water pump pulley should be necessary at all with stock components. Is there any error that could have been made when the bottom end of the motor was assembled? I will now have to reposition the alternator and power steering pump before I can retest.
 

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Chris, just a thought, does your car have a fan clutch or special fan? I threw the belts on one of my cars last year and it turns out that the bearings or whatever in the water pump where the fan attaches, had worn out due to an out of balance fan/fan clutch. There was enough wobble in the water pump itself to allow the belts to jump off the pulley mounted to the water pump. Like your situation, this only happened when I was really getting after it and rpms were north or 4,000 or so.

[This message has been edited by denverRS/SS (edited 09-29-2000).]
 
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