Mystery squeal under power. Name that tune?

[DinoShepherd]

1990 m923a2. Ft. Lewis rebuild in 2012. Very nice shape. Slowly piecing together the little stuff uncle sugar missed.

When I got it, it had a chirp under the hood at idle. It would also squeal like a pig under power, uphill at over 1900rpm uphill only. Not through acceleration at that rpm, Only under heavy load. This may be a clue.

Water on the belt would make the chirp go away at idle. I changed the tensioner and belt. No more chirp at idle. Happiness.

The squeal that sounds like belt slipping is still there under heavy power, uphill is still there. But I am thinking it may not be related to the belt. It goes away when I back off on the gas a bit.

Is is it possible it has something to do with fueling or turbo? It really does not sound healthy and is quite loud.

Thanks in advance. BTW, I checked the TM and it said to ask you guys.

 

[Scar59]

Still sounds belt related, air compressor/belt may be the next area to look at. Some belts get smooth and never grip under power.

 

[Ford Mechanic]

Anyway to duplicate it at a standstill? Tried power breaking it to see if the noise happens? Could be a turbo bearing. .....

 

[Jericho]

air compressor , clean the pullies, change the belts, mine does the same sometimes, especially if I get it wet or if I havnt driven it in a while

 

[DinoShepherd]

OK, I will change the compressor belt.

Still new at this so bear with me please...

I thought the A2 had a gear driven compressor, but I will press on. I checked the PN cross reference for a number, but couldn't find one. Anybody?

Oh, no way to duplicate at idle or at standstill while power breaking.

Thanks again for all the thoughts.

 

[Suprman]

I have had alternators, belt tensioner pulleys and water pumps do that to me. You can rule out the tensioner by spraying a bit of wd40 on the shaft area.

 

[JohnnyBM931A2]

I have had alternators, belt tensioner pulleys and water pumps do that to me. You can rule out the tensioner by spraying a bit of wd40 on the shaft area.

He's already replaced the tensioner. However, it is entirely possible that it could have been bad right out of the box.

 

[Suprman]

Water pump maybe. If the alternator bearings are bad just a matter of time before it smokes up.

 

[Coffey1]

There is only 1 belt on the 8.3

 

[74M35A2]

Any chance you spun each belt driven accessory pulley while the belt was off to check for difficult resistance? Also, take the belt off and go for a spin around the block or down the street. The motor will not overheat without the water pump spinning for that short of a time. Alt and fan clutch will be fine also. This will eliminate all the belt driven accessories out of the equation so you can determine if your noise is sourced from them.

 

[DinoShepherd]

Any chance you spun each belt driven accessory pulley while the belt was off to check for difficult resistance? Also, take the belt off and go for a spin around the block or down the street. The motor will not overheat without the water pump spinning for that short of a time. Alt and fan clutch will be fine also. This will eliminate all the belt driven accessories out of the equation so you can determine if your noise is sourced from them.

thanks for the note. Late nite in MI?

Serpentine belt. So no joy on scientifically eliminating them. All or nothing.

I spun the alternator and water pump when I replaced the tensioner. Smooth with low effort in both.

The squeal is only, only uphill under heavy load at higher rpm. It's crazy.

 

[WillWagner]

If it squeals under a load only, either an exhaust leak before the turbo, like a manifold gasket or the turbo mount gasket, or a compressed air leak, not as in truck system, but compressed combustion air. Look at the clamps for the crossover pipe. Look at the aftercooler mount bolts and the area where the fuel line bundles are secured to the head, those are the same capscrews that mount the aftercooler. If one is missing, it will whistle or if one that is too long was jammed into a hole there is no clamping force on the gasket, so it whistles. BTW, the C is metric, so, if you see an SAE bolt in a hole, that could be your issue too.

 

[dilligaf13]

Baby powder on the belts also help quite them down. Mine started squealing at idle, a little baby powder and the squeal was gone. Don't try putting it on while the fans activated though....

 

[DinoShepherd]

If it squeals under a load only, either an exhaust leak before the turbo, like a manifold gasket or the turbo mount gasket, or a compressed air leak, not as in truck system, but compressed combustion air. Look at the clamps for the crossover pipe. Look at the aftercooler mount bolts and the area where the fuel line bundles are secured to the head, those are the same capscrews that mount the aftercooler. If one is missing, it will whistle or if one that is too long was jammed into a hole there is no clamping force on the gasket, so it whistles. BTW, the C is metric, so, if you see an SAE bolt in a hole, that could be your issue too.

Thanks. I was thinking the same thing. I think the other belt issue was a red herring. The only under load aspect led me to that. We will see how good our detective work is.

I was thinking bad turbo bearing, but air from between sealing surface post.turbo makes more sense.

I read ear that correctly, right? You are thinking some sealing surface post turbo?

if it's been blowing air through a gasket end surface, especially hot air, is the gasket likely blown too?

 

[Jericho]

Using a long screw driver with a wooden handle or a mechcanics stethoscope listen to the assemblies whether on mount brackets or on the block, each assembly turns at a different cyclic rate (CPS) so you can tell which assembly is making noise by approximating the CPS aurally. Place the screw driver on the anvil of your ear lobe, BE CAREFULL NOT TO GET IT CAUGHT IN ANY ROTATING ASSEMBLIES, INJURY WILL RESULT ! I prefer the wooden handled screw driver my self. Even a slipping belt is discernable, The individual roller bearings can be heard when listening carefully.

 

[Jericho]

turbo exaust gas leaks are usually easily detected, look for black diesel residue, clean up the flanges well and drive it then re-inspect Or use a lazer temp gage and look for leaks, you will see the leak in a small variation in the flange surface, pass the lazer dot slowly all around the flange area watching for a slight shift in temp, works for me and have used it on everything from a M-35a2 to an F-16 Viper Jet Engine.

 

[DinoShepherd]

Thank you all. I will report back.

Again kind of new at this, but let me give you all findings.

Four mounting bolts on each side of the turbo. 4 10mm bolts on the compressor side and 4 13mm bolts on the exhaust side. All tight.

Turbo to exhaust manifold. Tight.

Then we move to the flexible sections attached to the actual turbo. Hose clamp tight on both ends.

Then we have the two short (4" or so) sections of silicone hose that connect to the intake on top of the engine. All tight.

Now lets check the hose clamp to the actual manifold. Loose. Interesting.

I could see see pressurized air getting past and the hose acting like a reed making a squealing noise. The hose clamp is under the manifold and hard to get to. I could see it getting missed during an inspection.

Does that seem possible to you all?
Did I miss any bolts or fasteners along the way?

It's dark and I am done for the nite, but I will let you all know if I got it.

Thanks again for following along. Hopefully, this will help someone else in the future.

 

[Ford Mechanic]

Definitely possible, hope that fixed it!

 

[WillWagner]

You have most likely found it. And, an FYI for all that say a "turbo bearing" The bearing isn't a bearing. No moving parts. It is just a bronze bushing that floats and centers itself when the shaft spins there is a thrust on each side of the center housing. If the "bearing" fails, you will have oil out the exhaust and/or in the compressor housing of the turbo.

 

[Ford Mechanic]

You have most likely found it. And, an FYI for all that say a "turbo bearing" The bearing isn't a bearing. No moving parts. It is just a bronze bushing that floats and centers itself when the shaft spins there is a thrust on each side of the center housing. If the "bearing" fails, you will have oil out the exhaust and/or in the compressor housing of the turbo.

Yeah, good point. I had a lapse and thought it had ball bearings in there. And I should have known better.