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Discussion Starter · #1 ·
69 Chevy C10 big block
Belt squeals at start and high rpm. PS pump was misaligned so I replaced the pump and brackets only to discover it's actually the fan/alternator belt that's squealing. Oh well, now I have a new PS pump.
The belt is new. It was rubbing on the lower alternator bolt so I fixed that problem. Alternator is aligned, tension is good. Tried belt dressing, no help. So my question is about that alternator pulley. The belt fits but sits deep. Could that somehow be causing my problem? I'm running out of things to try.
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Wrong belt, it sits too deep in the pulley. You need to measure the width at the top of the pulley do that on all of them thst the belt in question loops to be sure the pulleys don't have miss-matched widths and depths. Basically, the pictured belt isn’t big enough for the loads put on it. By bigness I mean the side surface area of the belt in contact with the inside angled surface of the pulley. The belt should not make contact with the bottom of the V groove, close but not touching. It’s the sides of the V belt that does the work so you don’t want it running bottom of belt to bottom of groove. “Groove” brings back pleasant memories of living in Pacific Beach, Calif. going to the movies with a wild red head named Jackie to see Groove Tube, Barberella and Rocky Horror Picture Show in an all night extravaganza. That was a long time ago.

Get some measurements as in groove width and depth and needed length over the driving snd driven pulleys the belt needs to encompass so we can go to the catalogs to see what’s needed. This may be an ordeal at the parts store as modern references are often wrong and the Gen-Z’ers behind the counter have no personal data base outside their computer link that often has faulty info.

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Discussion Starter · #4 ·
Well this is funny. I found a brand new belt under the seat that I bought in 2015. It is wider and fits better. But it still squeals, quite loud.
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It still looks too deep in the pulley. Additionally the pulley grooves probably need to be cleaned and roughed up a little to give the belt some bite.

I‘d also check to see if there is something at the end of its adjustment such that you’re not getting enough tension on the belt and check for free rotation of the devices the belt is turning to be sure there isn’t a failing bearing on something. Obviously a squeeling belt is indicating something isn’t right in how deep or wide it is compared to the pulley grooves, insufficient tension, rubber and debris burnt into the pulleys, glazed belts, or excessive turning resistance by an accessory which could be a miss alignment to the belt or a bearing failing. Possibly a loose or failing mounting bracket, boss or fastener.

Possibly moisture or temperature changes affecting grip or tension. I get a little of this on frankenmouse some mornings in the winter till the engine gets warmed up when it’s been wet and cold overnight. So the belt and pulleys are probably damp the engine and accessories are cold shrunk lowering belt tension and I’m pulling a lot of power off the alternator to run all the lighting, heater at max speed, wipers running, and to restore cranking power to the battery so the morning winter electrical load where I live is pretty high. No stereo any more after the 3rd or 4th time it was broken into to steal the stereo equipment and fighting with the damn insurance company so I just took it all out.

Then the theft ring got caught, it was a huge organization working all of Puget Sound, stealing cars to construction equipment, car stereos, tools, computers, cell phones, etc that are left in vehicles. They had several all metal buildings including one where a group of them lived where they stored these stolen vehicles and stuff. Turned out one night one of the girl friends was sent out to the storage building to retrieve some beer from the ‘fridge in there and she forgot to close the door when she went back to the party. Inside was a stolen new Caddy that was transmitting its location to On-Star. Since to door was left open the RF got out, since the car was on the cops stolen vehicle list and they monitor On-Star all of a sudden this stolen VIN number shows up with coordinates as to where it is. The sent a cop to investigate when he got there he radioed for a warrant and lots of backup. This took a big bite out of vehicle and machinery thefts for a long time in this area.

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Discussion Starter · #6 ·
Appreciate your diligence and thoroughness. Of the things you mention I think the pulley size and surface is most applicable, the others don't apply in this case. Are you still in Puget Sound? I am as well, so yes I understand cold and humidity, but this is a year-round problem.

If the belt is too deep I would need to get a narrower pulley. A wider belt would be too wide for the crank and fan pulleys. Shopping online at Summit, they don't even list groove width so there must be a standard width.

What about a 2-groove pulley? Would that fix it? I have room for it.
 

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For the right combination of belt and pulley the outside of the belt should be flush with the outside of the pulley. It appears you need a different alternator pulley.
 

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I have a collection of alternatiors just for this situation. You never know when your going to need a pulley or to swap out a alternatior on a Sunday night.


Use your crank as a refrence as far as belt angles go. Once you know the belt angle you can easily order a belt. Looking at that tensioner it looks like you can loose a inch or two in belt length. If that is what I think it is the further to the drivers side the more the bracket/alternatior case can twist as the belt pulls on it. So using a smaller belt will help.
 

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Let's take a step back here and get some background information...

I could be wrong, but that looks like the factory Hi-Perf alternator pulley, used on all Solid Lifter cam/high performance original applications like 327"/350-365 hp, 350"/350-370 hp, 396"/ 375 hp and 427"-454"/425+HP applications......And is supposed to be deep groove for belt retention at high rpm..

It is still sold by resto parts companies.
it is different diameter and different construction that the standard low perf alternator pulley. Hi perf is a machined piece from solid bar stock, the low perf is two stamped halves welded together.
Here's an example:
1964-1977 Chevelle Deep Groove Alternator Pulley (ss396.com)

Stock pulley is different:
1964-1977 Chevelle Alternator Pulley Correct (ss396.com)

As long as the bottom of the belt isn't riding on the very bottom of the V- groove I would be looking elsewhere for the squeal.

Hard to tell from the picture....but is the alternator belt being driven by the water pump pulley only??
It isn't also going around the crank pulley??
Because it should be......driving off just the water pump pulley means the crank to waterpump belt is carrying a double load and is likely the one squealing.....and not the actual alternator belt.

Factory belt routing would have been crank, water pump, alternator on one belt, crank to power steering pulley on a separate single belt.

Post up some more pictures from a little further away, and different angles so we can see the whole front of the engine and belt drives.
 

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Hope GM didn't do the ridiculous compound drive scheme like on BB Vettes. Yep that looks like the factory large dia. machined deep groove pulley, I have one on my El Camino which I transferred from alternator to alternator over the years.

Find out exactly where the squeal is coming from by spraying Windex onto individual pulleys and listening for the difference.
 

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Meaning, spray Windex while the motor is running, from a safe distance, with a nozzle set on stream.
 

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Discussion Starter · #12 ·
I could be wrong, but that looks like the factory Hi-Perf alternator pulley, used on all Solid Lifter cam/high performance original applications like 327"/350-365 hp, 350"/350-370 hp, 396"/ 375 hp and 427"-454"/425+HP applications......And is supposed to be deep groove for belt retention at high rpm..
Yes, from your links I would say it is the deep groove, 3-1/8" dia.
As long as the bottom of the belt isn't riding on the very bottom of the V- groove I would be looking elsewhere for the squeal.
Belt is Napa 257570, .41" or 13/32". Wider than the belt in my original post so I'm quite certain it's not bottoming out.
Factory belt routing would have been crank, water pump, alternator on one belt, crank to power steering pulley on a separate single belt.
Exactly right. And just to confirm, I have run both belts separately and the PS pump belt is silent. If I can find some Windex I will try the squirt test. Thanks for all the suggestions.
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You have one belt turning the mechanical fan. I'd be looking real hard at the belt routing you have going on there as the contact area of the fan is pretty short for the load it's under.
 

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Discussion Starter · #14 ·
You have one belt turning the mechanical fan. I'd be looking real hard at the belt routing you have going on there as the contact area of the fan is pretty short for the load it's under.
I don't understand. Is there a better way to route the belts?
 

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Eric gotcha up there somewhere.
Belt goes around the crank water pump, alternator.
First pic tells you everything you need to know
 

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Maybe it is the camera angle. But both those belts look to be on there crooked. This can cause slipping or walking up a pulley.

If you measure off the block by the crank pulley then as far as you can up the belt to the block/head the measurements should be the same.

Your crank and waterpump pulley are not a match. You should be able to run 2 belts on the waterpump.
 

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Discussion Starter · #17 ·
Maybe my photos are misleading. The belt does go around crank, waterpump, alt. I don't see any other way to route it.
I could not isolate with windex. At 3000 rpm it just sprays everywhere. But it may well be the waterpump pulley, the noise seems to be more central.
The crank and waterpump pulley do match. I can add another belt if I get a 2-groove alt pulley. Will that solve the problem by doubling surface contact on the waterpump pulley?
 

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SLM has this just started? Had you installed something new to the truck electrical system.

How old is the battery?

As many have said, pulley alignment, pulley groves need to be the same and proper belt width are all important.

Another thing that could be problem, is that for some reason the alternator is being triggered into full load at start and idle. Which a single V belt will not handle at idle.
 

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You have one belt turning the mechanical fan. I'd be looking real hard at the belt routing you have going on there as the contact area of the fan is pretty short for the load it's under.
I agree, squeal is likely coming from the small amount of contact the belt has with the water pump pulley, less than 1/4 of the diameter.
The rigid fan will make this more noticeable too, compared to a clutch fan. The direct drive fan takes more HP to drive than the actual water pump does.
You could test it without the fan, just to see if the added load of the rigid fan at the waterpump pulley is a big part of the problem.

Dual belts can be a fix since you have an unused groove, either a duplicate of the current route and a dual groove pulley on the Alternator, .....or just add a short single belt around just the crank and water pump as a main drive to the pump and fan (PITA to get put on there though).

Check 95 Trucks suggestion of full charging load at idle also being a factor.
 
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