After I installed my A/C, my alternator belt melted. Same with a second belt. Pulley on the alternator is moving freely. Alternator appears to be charging fine. Any idea?
Belt melting
- Thread starter skywalker
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Definitely on the right pulley - really hard to mess that up on this one. Definitely not misaligned - if the alignment is off at all it's to slight to tell with the eye which wouldn't cause this much friction.
It's a v-belt pulley system so the only thing that could go opposite is the water pump. The only difference from before is that the crank shaft now has three grooves, the outer groove has a belt for the compressor - crank -> tensioner -> compressor. But only the alternator belt is a problem - it's crank -> alternator -> water pump. the middle belt is crank -> water pump -> PS pump. But those are routed exactly as before. There's really no way to mis-route the belts.
horseballz
10 Year Member
Alternator & power steering belt need to be EXACTLY the same width, otherwise one is trying to move at a different speed than the other. I suggest both of these belts be purchased at the same time in the same brand and , obviously, the same series, IE: 14xxx, 15xxx or 17xxx. For example, even though your local Auto Zone might be able to cross your Dayco, Goodyear or Gates belt to one of their "Duralast" belts, it will likely not be the same width, taper or compound of rubber. Let us know how it works out.
HTH,
Gene
HTH,
Gene
That makes zero sense to me:
The speed at which a belt travels is not related to the width, it's related to the length. Let's say belt A is 1 foot long and belt B is 2 feet long. If they have the same RPM (which in this case, they do since the crank is providing the rotational force) then belt B will have to move twice as fast. In this case, the alternator belt is shorter, (I measured, it's about 5 inches shorter.) So the alternator belt is moving slower. Same concept on a helicopter - a blade spins the same RPM at the shaft and the tip, but the tip is moving faster because it has more ground to cover per revolution.
Either way, doesn't matter, the first belt that melted came from NAPA as did the other two belts. Also, the stock belt for the A/C is in pulley that is thicker and has a stoker thicker belt. Doesn't affect the speed. Also doesn't say why the change came after I installed A/C - same belts as before and yet suddenly the belt burns up?
Hack
15 Year Member
No I think what was posted before makes perfect sense. The pulley has a v shape, as does the belt. If the belt is wider it has to ride farther out on the pulley. For every time the pulley rotates, the belt moves a distance equal to the circumference of the crankshaft pulley (at the location where the belt rides on the crank pulley).
SO - if you have a narrow belt it will ride deeper in the pulley and it won't move as far. A wider belt will be closer to the outer edge of the pulley and will move farther for each engine revolution.
The same holds true if both belts are the same width but the tension is very unequal between the belts. Higher tension will suck a V-belt deeper into the pulley groove, and it won't move as far for each engine revolution.
Bottom line IMO is V-belts suck compared to a modern serpentine belt. If you follow the previous poster's advice and are careful with the belt tension you should be ok, though. My first thought is that it might be more caused by a significant difference in belt tension or the belts just being too tight rather than belt width, but I would still replace all the belts at once with the same brand as advised above. Also, make sure you don't over-tighten the new belts.
There won't be any difference in speed due to the belt riding deeper in the groove - the a 21 inch long belt rotating at 1000rpm is traveling at 21000 inches per minute (roughly 20mph.) That doesn't change if it's barely in the groove (thicker belt) or all the way in the groove (thinner belt.) One revolution of the belt is still the same 21 inches. The idea that you need the same brand, rubber compound and such is ridiculous and snake oil - also impossible given that the third belt HAS to be thicker - the groove for the A/C belt is roughly 50% thicker. If I put a belt that thick on the other grooves they'd not fit! And as I said, when he first belt melted they were all from NAPA. The belts are in different grooves - that they all move at different speeds is a given.
A thinner belt just means that component's tension puller (in this case the alternator itself) has to be pulled tighter to get the tension that will allow rotation.
Again - the speed of the belt is the length times the number of revolutions per minute. so 10 inch belt at 1000rpm is 10000 inches/minute. If the belt isn't going that fast then there is too little tension and the belt is slipping - and I'd hear that.
The tension thing is something to try though. I'm just not seeing how I could have that too tight. There's no squeal so I'm not thinking it's too loose. I've only got two hands and there isn't a good way to pry it, so getting it super tight is nigh to impossible. but I'll loosen it and give it a shot. I think I said it was a 2G but that's a typo. It's a 3G. Can anyone imagine the alternator itself overheating?
If your alt is bad, under a heavy load your alt will try to run backwards, IE if your drawing more from the system then the alt can produce. What happens is the diode in the alt prevents battery power from trying to spin the alt like a electric motor, hence the reverse rotation and possible belt melting? It's a theory.
It's a 150A alternator so I'm def not over-drawing (no radio, had the problem with no lights had the A/C off), but a bad alternator isn't out of the question. I'll crank it again in the morning and see if I burn the belt up. I adjust the tension a little a few minutes ago and did a quick crank. I loosened it first - had some squealing and a little bit o' vapor from it. quickly turned it off. Tightened it and no visible fumes and less heat. I think I had enough tension not to squeal but enough to slip a little under the load. We'll see in the morning. All the heat is definitely on the alternator pulley though.
Hack
15 Year Member
The speed of the belt has nothing to do with the length of the belt. The belt doesn't rotate at engine rpm. It rotates at a speed defined by the diameter of the crank pulley. I think it should be elementary, but maybe you sincerely don't understand. I'll try to explain.
Let me step you through this - tell me where you disagree.
1. The belt is driven by the crankshaft pulley.
2. All other pulleys are along for the ride. In other words, their rotation is driven by the belt.
2. The belt does not slip on the crankshaft pulley.
3. The crankshaft pulley rotates at the engine speed due to being connected to the crank.
4. When the crankshaft pulley rotates 1 time, the distance a point on the perimeter of the pulley moves is equal to the circumference of the pulley (the circumference is 2 x pi x radius). Remember the belt doesn't slip on the pulley. If you took a piece of string and cut it so it would fit exactly one time around the pulley, the length of the string would equal the circumference of the pulley.
5. If the crank pulley were smaller, the circumference of the pulley would be smaller (remember circumference is the length of a string that fits exactly one time around the outside of the pulley - smaller pulley = shorter string). The number of revolutions per minute of the crank pulley is still the same as the engine, but now the speed of the belt is reduced.
Think about how under-drive pulleys work. They save horsepower by changing pulley sizes (hence slowing down the belt and reducing the rotation speed of the accessories). That's why people who use under-drive pulleys have problems like overheating or alternators that don't charge well at idle. Under drive pulleys don't appreciably change belt length. Either the crank pulley gets smaller or the driven pulleys get larger, or both. That slows the belt down.
Here's another way to think about it. The belt is like the chain on a bike. The chain is linked to the pedals. If you shift to the big sprocket in front and keep pedalling just as fast, the bike goes faster. That's the same as a belt on a car accessory drive. If the V-belt is wider, it rides farther out on the pulley - like shifting the chain to the larger sprocket attached to the pedals.
I hope this is helpful. I'm sure you'll get it if you think about it for a second.
Hack
15 Year Member
Easy enough to take the alternator and get it tested. I hope you find the problem.
The speed of the belt has nothing to do with the length of the belt. The belt doesn't rotate at engine rpm. It rotates at a speed defined by the diameter of the crank pulley. I think it should be elementary, but maybe you sincerely don't understand. I'll try to explain.
Let me step you through this - tell me where you disagree.
1. The belt is driven by the crankshaft pulley.
2. All other pulleys are along for the ride. In other words, their rotation is driven by the belt.
2. The belt does not slip on the crankshaft pulley.
3. The crankshaft pulley rotates at the engine speed due to being connected to the crank.
4. When the crankshaft pulley rotates 1 time, the distance a point on the perimeter of the pulley moves is equal to the circumference of the pulley (the circumference is 2 x pi x radius). Remember the belt doesn't slip on the pulley. If you took a piece of string and cut it so it would fit exactly one time around the pulley, the length of the string would equal the circumference of the pulley.
5. If the crank pulley were smaller, the circumference of the pulley would be smaller (remember circumference is the length of a string that fits exactly one time around the outside of the pulley - smaller pulley = shorter string). The number of revolutions per minute of the crank pulley is still the same as the engine, but now the speed of the belt is reduced.
Think about how under-drive pulleys work. They save horsepower by changing pulley sizes (hence slowing down the belt and reducing the rotation speed of the accessories). That's why people who use under-drive pulleys have problems like overheating or alternators that don't charge well at idle. Under drive pulleys don't appreciably change belt length. Either the crank pulley gets smaller or the driven pulleys get larger, or both. That slows the belt down.
Here's another way to think about it. The belt is like the chain on a bike. The chain is linked to the pedals. If you shift to the big sprocket in front and keep pedalling just as fast, the bike goes faster. That's the same as a belt on a car accessory drive. If the V-belt is wider, it rides farther out on the pulley - like shifting the chain to the larger sprocket attached to the pedals.
I hope this is helpful. I'm sure you'll get it if you think about it for a second.
That's not what was said earlier though - and an under drive pulley means the ACCESSORY is moving slower or faster- not the belt.
Either way - it's a bad alternator
I stopped last night before going to see a movie, picked on up, had them swap the pulley and I put it on when I got home. Took it out this morning - car ran better a lot better, can actually touch the alternator (that's how I figured out what it was - alternator would burn my hand if I touched it, much less the pulley) so all is well in mudville - and my Yellow Jackets put up 66 points and 768 yards so it's a good day!
Hack
15 Year Member
That's not what was said earlier though - and an under drive pulley means the ACCESSORY is moving slower or faster- not the belt.
Either way - it's a bad alternator
I'm glad you solved the problem. I will stop trying to help you understand how belts and pulleys work.
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