# Rattling noise from front of engine



## Bing68 (Nov 4, 2019)

Hi all, have acquired a new noise of late, quite intermittent, never when cold, but not all times when hot. Thought it was a bad bearing in the alternator, pulled the belt off, noise went away. Replaced alternator, sounded good for a test drive. Next day, sound came back.....hoping someone's ear might recognize the sound. Any thoughts would be appreciated.
Steve


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## PontiacJim (Dec 29, 2012)

Sounds like a bearing to me as well. Looking at the alternator's fan behind the pulley, it does not seem to rotate smooth. I know you just installed another. Make sure it is not hitting one of the bracket bolts.

I would remove the belts again as you did. Pull the Alt belt and run. Then pull the water pump belt and run the engine. You can run it for a few minutes and it won't hurt anything. 

It could be a water pump bearing, but usually the water pump will begin to seep water out of the weep hole on the water pump shaft when it is going bad. Grab the pulley, engine not running, and see if it has wiggle/play.

I would also check the bolts that hold the pulleys to the harmonic balancer and that large bolt that holds the balancer MUST be torque to 160 ft lbs. If it loosens up, the balancer hub that fits over the crank snout can crack and even break off. So with belts off, I would give the balancer a check and grab it by hand and rock it back and forth feeling for any unusual play/movement.

Spin the fan by hand to make sure it is not hitting anything and you have sufficient clearance around the fan blades.

Make sure you do not over tighten the belts. You should be able to press down on them and they deflect about 1/8" or so. Too tight and you burn up the Alt & water pump bearing rather quickly.


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## Lemans guy (Oct 14, 2014)

Recheck the four bolts that secure the fan to the pump and make sure they are not loose


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## BLK69JUDGE (Jun 10, 2010)

and get the other upper alternator adjuster bracket


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## Bing68 (Nov 4, 2019)

Whatcha mean by other bracket?


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## O52 (Jan 27, 2019)

68 Power steering cars use two alternator brackets


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## Bing68 (Nov 4, 2019)

So I got another alternator to n a warranty exchange, same thing, after about 30 minutes of drive the clanking/rattling is back. 
Fan bolts are tight
Pulleys seem tight
Fan spins freely
Gonna pull the water pump belt tomorrow, problem is that the noise can disappear after 5 minutes of shut down. So firing it up after taking the belt off may not prove anything. 
I will trudge on...
Thx
Steve


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## the65gto (Oct 9, 2008)

Have you tried the screw driver in the ear trick. (handle in ear, blade on device) It amplifies the sound. Go from alternator to WP etc.


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## PontiacJim (Dec 29, 2012)

You can also buy a mechanic's stethoscope if you want to get fancy. Most auto stores sell these. If you have a Harbor Frieght, here is one cheap. Mechanic's Stethoscope


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## Lemans guy (Oct 14, 2014)

How is your hydraulic fan clutch? It operates on temperature or RPM.....two different types

on temp clutch it comes on when hot and locks in, slips when cold....so you are interpreting cold/hot change in sound.....is it operating correctly?

Or half engaging when hot,...? ......malfunctioning parts can make weird sounds...


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## Ralph D (Feb 13, 2020)

I bet the water pump bearing is bad


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## Jd70 (Jul 4, 2019)

1. Use a stick, dowel, a really long screwdriver, long extension, mechanic stethoscope, anything like that you can put to your ear And place against device. BE CAREFUL where you place it because you’ll be doing this while the engine is RUNNING. You are just trying to narrow down where the sound is coming from, place against a safe place on alternator, ps pump, etc.

2. Sounds like the power steering pump to me. Not a bearing noise.

3. Try new belts. There can be dirt embedded in the belt and it’ll make noise when it “hits” a pulley.

JD


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## Jd70 (Jul 4, 2019)

The first part of this video pertains to using a long screwdriver, but Ive used any solid long something wood whatevers handy, you’ll get the idea


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## Jd70 (Jul 4, 2019)

Sorry paste fail hers video link






JD


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## Bing68 (Nov 4, 2019)

Resurrecting this discussion, car was in the shop for something else and my mechanic suggested that the noise was a result of the belts rotating at different speeds on a common pulley. Turns out, the outer groove on the pulleys for the power steering circuit is wider than the inner grooves for the alternator.
Not sure what the actual sizes are, but I have a roughly 3/8 wide belt (stock size) on the alternator, I bought a 1/2 inch utility belt and put it on the steering side. What a difference, not perfect but 90% better.
Basically, I was running 2 3/8 inch wide belts on a pulley that has a 3/8 groove and a 1/2 inch groove.
The 68 belts are both the narrow ones, so I looked at the back of the block by the distributor and discovered that I have a 71 block. So I ordered a P/S belt for a 71 GTO, same width as the 68.
Any idea where these pulleys came from with the 2 different widths? I just want to order a PS belt that fits this pulley.


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## Mine'sa66 (Oct 30, 2019)

Doesn't sound like a bearing noise to me either. Different width belts on the same pulley is done all the time. That doesn't change the speed at which they rotate the common pulley. Water pumps make a distinct noise. Doesn't sound like that to me. Perhaps the PS pump. It sounds like movement, WP pulley bolts as mentioned. Alternator cooling fan movement. Something's heating up, changing dimension, causing interference, or the internals of the PS pump.


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## Bing68 (Nov 4, 2019)

I agree that the different belt widths aren't a problem provided you have the proper belts for the pulleys. For the 68, they are both 0.44 inch wide belts, 
The pulley on my car is .44 for the alternator, but wider for the PS. If I run stock .44 belts, they are in fact rotating at different speeds. With the 1/2 inch utility belt on the PS side it is much better but not perfect, as you can see from the pic, it is ever so slightly too large.


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## Mine'sa66 (Oct 30, 2019)

Bing68 said:


> I agree that the different belt widths aren't a problem provided you have the proper belts for the pulleys. For the 68, they are both 0.44 inch wide belts,
> The pulley on my car is .44 for the alternator, but wider for the PS. If I run stock .44 belts, they are in fact rotating at different speeds. With the 1/2 inch utility belt on the PS side it is much better but not perfect, as you can see from the pic, it is ever so slightly too large.


Yes, they run at different speeds. Which has nothing to do with the common pulley. Remember, the alternator and PS pump are free to spin at any speed they want.


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## Lemans guy (Oct 14, 2014)

Still sounds like a loose fan, did you check tightness of the Four fan to clutch bolts?


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## Lemans guy (Oct 14, 2014)

Sorry Steve, I missed where you did check that.


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## gtojoe68 (Jan 4, 2019)

Don't forget to get the other alternator bracket. Really important. I can send pic from my 68 if need be. Let me know


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## Bing68 (Nov 4, 2019)

Yes, fan bolts are tight.
Maybe I just have a misunderstanding of how the different speed belts work. The crank pulley drives both belts. The crank pulley has an inside groove for a .44 inch wide belt. The outside groove is for a wider belt (as I said, I put a 1/2 inch utility belt on temporarily). With the stock .44 belts on, they are rotating at different speeds when they hit the fan pulley which also has the different width grooves. I understand that the alternator and ps pump are independent, but the crank and fan pulleys are not.


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## Mine'sa66 (Oct 30, 2019)

Bing68 said:


> Yes, fan bolts are tight.
> Maybe I just have a misunderstanding of how the different speed belts work. The crank pulley drives both belts. The crank pulley has an inside groove for a .44 inch wide belt. The outside groove is for a wider belt (as I said, I put a 1/2 inch utility belt on temporarily). With the stock .44 belts on, they are rotating at different speeds when they hit the fan pulley which also has the different width grooves. I understand that the alternator and ps pump are independent, but the crank and fan pulleys are not.


Both belts are spinning around the common pulley. If the thinner belt is taking a shorter path around the common pulley, it's just going to spin whichever accessory it's turning at a faster rate. If both of the belts went to the same load, and one was thinner, then yes, something would have to give.
Yes, the fan and crank are connected, but each of the belts that connect them have an independent pulley in their loop to make up the difference.
Have you eliminated 1 belt at a time to see how that effects your noise?


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## RMTZ67 (Mar 12, 2011)

Fan hitting the shroud at the bottom? I had that problem.


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## PontiacJim (Dec 29, 2012)

As I see it, the width of the belt could play a role as to how it seats down in the pulley. It would be how deep into the pulley groove that could cause an issue as often times the store bought belts are essentially metric and are thinner and do not have the correct "V" pitch of 36 degrees on the belt that matches the original - they can seat too deep and slip or ride on the inner portion of the pulley and not grip the sides of the pulley grooves. The height of the belt, from the bottom of "V" to the top of the belt needs to be the same - factory belt measures 5/16" thick from top to bottom.

From the factory Service Manual for 1968. Water Pump & Generator Belt - 3/8" wide. Power Steering Pump Belt - 15/32" wide. No length seems to be given.

The Pontiac Chassis Part Manual, Group 1.000, shows this for the belts.

Alt. Belt, 1968-69 w/o 62 Amp Alt. - Part No. 9433753: 50 1/2" long, 7/16" wide, 36 degree pitch, 5/16" thick (top to bottom)
PS Belt, 1967-70 - Part No. 9433755: 51 1/2" long, ? wide, 36 degree pitch, 5/16" thick.

The Restoration Guide shows for 1968 & 1969, Alt & PS as:
Alt Belt - 3/8" wide x 50" long.
PS Belt - 1/2" wide x 52" long.

Note - The PS steering belt 9433755 was not listed in the Pontiac Part Manual, it was skipped. "3754" showed 51" long, "3756" showed 52" long, so it would make sense that "3755" was 51 1/2" long. The width is unknown, but if you have the wider pulley, my guess is it is the 1/2 wide?

So as you can see, a varied number of widths and lengths for the Alt/PS belts. These belts are also without the 62 Amp Alt. which I believe uses a different pulley size? The Alt & PS are adjustable so the range of lengths can really vary a little. The important thing is the V-belt pitch of 36 degrees that matches your pulley grooves and they need to be the same thickness of 5/16" as measured from the top of the belt to the bottom of the V. This ensures the belts ride at the correct depth within the pulley grooves.

Just for fun, I would also check the torque on the balancer bolt. It has to be torqued to 160 ft lbs which is quite a bit, and if someone did not have a torque wrench to correctly torque it down, ie engine rebuild or timing chain replacement, it can back out and become loose and even crack on the crank snout and do damage. I would not rule this out as you look for the noise.


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## David Shuff (Mar 31, 2018)

It gets down to the pitch diameters of the crank and water pump pulleys. This requires the correct v belts to achieve harmony. Mines’sa66 assessment is incorrect. The reaction of the alternator and PS pulleys has no bearing on this situation. Why Pontiac went with this design is about as crazy as using a ¼” bolt to secure the water pump to the intake.


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## Mine'sa66 (Oct 30, 2019)

I've said my piece. If everybody thinks a 1/16" diameter difference is making that noise, then you have your solution. There's (was) about a zillion Mopar slant 6's out there with twin belts to the alternator. Rarely were those belts identical. They didn't make noise. Jim has given a large list of belts with minor differences. With all those possibilities, manufacturers and wear states, you'd think with so many Pontiacs on the road, there would be all sorts of belt noise issues, but there aren't.
I own one of these. The 2 belts on mine are certainly not a perfect match. Same diameter, one rides high, one rides low. No noise.
Is there some sort of harmony issue between WP and balancer pulley? I'm sure there is, I learn something new everyday. We'll see if that's his issue.
Good luck to the OP. I hope he sorts it out cheap and easy.
Take care,


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## Bing68 (Nov 4, 2019)

Thank you Pontiac Jim, that is what I was missing, the local parts monger has supplied me with two 3/8 wide belts, so I assumed I had some strange pulleys on my engine.
With the Specs and part numbers you have provided, I will now procure the proper belts. 
Thanks all for your patience 
Steve


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## PontiacJim (Dec 29, 2012)

Mine'sa66 said:


> I've said my piece. If everybody thinks a 1/16" diameter difference is making that noise, then you have your solution. There's (was) about a zillion Mopar slant 6's out there with twin belts to the alternator. Rarely were those belts identical. They didn't make noise. Jim has given a large list of belts with minor differences. With all those possibilities, manufacturers and wear states, you'd think with so many Pontiacs on the road, there would be all sorts of belt noise issues, but there aren't.
> I own one of these. The 2 belts on mine are certainly not a perfect match. Same diameter, one rides high, one rides low. No noise.
> Is there some sort of harmony issue between WP and balancer pulley? I'm sure there is, I learn something new everyday. We'll see if that's his issue.
> Good luck to the OP. I hope he sorts it out cheap and easy.
> Take care,


I do have to agree that I don't think it is a belt issue. But, I wanted to provide the belt specs so matching belt pitch angles and belt thickness could be matched to eliminate another cause of the noise.

I have had the experience of using the aftermarket belts that were narrower then stock, but was listed for the car. They went too deep in the pulley groove and rode on the inner hub not getting any traction. But, you know the sound of a slipping belt, I just could not figure out the issue as the belts were tight and from just looking, saw no issues. Finally figured that one out and went with the Dayco belts with the top cogs and the belts fit correctly and the flipping of the belts at high RPM's also went away - but that problem was really due to just a slight misalignment of the mis-matched pulleys I had. The Dayco belts just worked better even with the slight alignment issue and I never had another problem. Our cars aren't Ferrari's and those of that era had a lot of leeway with regards to tolerances - unlike today's engines.

Listening again to the video, it still sounds like a bearing, something hitting, or something loose. If the exhaust manifolds are still original, could be the butterfly valve found in there used to get the intake manifold heated up faster during cold starts. The bi-metal spring could be fluttering, the valve fluttering, or even a leak. This is why the mechanic's stethoscope comes in handy to at least isolate the area the noise is coming from as sound in an engine can travel.

May even be the PCV valve rattling, who knows. Many things it could be. So getting the matched belts just eliminates one more thing and will cure the issue or not.


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## PontiacJim (Dec 29, 2012)

Bing68 said:


> Thank you Pontiac Jim, that is what I was missing, the local parts monger has supplied me with two 3/8 wide belts, so I assumed I had some strange pulleys on my engine.
> With the Specs and part numbers you have provided, I will now procure the proper belts.
> Thanks all for your patience
> Steve


FYI, the part numbers are Pontiac, so it may not be of help. What you want to look at is the size, width, and pitch. As mentioned in the previous post, I used the Dayco brand belts having the top cog surface which worked good for me and I will use them again on my 455 build.

But the specs and lengths should help. However, as old as these cars are, there are no absolutes as parts get replaced and sometimes the same item is not used, but a substitute that works takes its place - that's old cars for you. So belt length can vary, but the key is to have a belt length that will allow you to tighten the belt. I have used various sizes, longer/smaller when the "correct" belt length was not available. Not really an issue as long as it can be tightened and does not run into/interfere with any part of the engine.

Do not over tighten the belts either. They do not get cinched down so tight you can stand on them and they don't flex. This is a guarantee in burning up the bearings in the Alt & water pump. The PS can take a little more as if it is too loose, it'll slip. You kinda learn as you go on this one.

The belts should be tight enough that you can push it in about 1/4" or so anywhere in the middle between 2 pulleys. My '73 Fury has double belts on the Alt, AC, water pump and on for the PS. I can watch the double belts flex in and out while the engine is running. Yep, they are a little loose and I do get belt squeal when I first fire it up, but once warm, that goes away. I will eventually tighten them up as it is a pain with Mopars, but for now, I don't drive it enough to really worry about it - it still is charging and water temps are good so it is not excessive, just loose.


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## 71 Lemans Sport (12 mo ago)

@PontiacJim hey just wanted to reach out and say thank you for your suggestions I see across this forum and this issue thread helped me. I usually just cruise in my 71 lemans sport 350 but about two weekends ago I was running late for a weekend shift I picked up and while on the freeway decided to take the spider webs out the mufflers and opened her up to about 90-100 for a short period of time. All was fine until after my shift when it was time to go home I turned the car on and heard what sounded like two marbles against metal coming from the front of the engine. I drove the car home and started to do some research and came across this forum. I removed the belts and boom the ticking noise went away. I cleaned the belts with some degreaser and installed the belts back on and nomore noise. I seriously thought the knock was an engine issue and was already regretting opening her up as I did lol. Thanks Jim and please share your Venmo if you have one so I can buy you a 12 pack.


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