Weird hollow sound from front bank 308

Boy that could be anything, do you have a stethoscope? or a long screwdriver to use as a makeshift one? source the noise a bit better and see what is sounds like without the body harmonics.

could be a loose cover, bad bearing or ??? hard to say.

 

Well, common sense would seem to suggest that if the noise wasn't there before you did something (timing belts, etc.), and then is there immediately after you did something --- there is a relation --- no matter how unlikely it may seem...

 

I do not know the answer to your question but I I did work with high speed manufacturing equipment so I have a thought or two.

Generally if the noise was not there and then you did something and it is now there, 99% of the time what you just did caused it. I know that sounds silly but I have chased my tail for weeks on something i thought could not be related, but in the end that is what caused it.

Also locating a sound is difficult. These noises bounce around and can fool even the most skillful ear.

A wining sound is a belt sound if i picture in my mind what you are saying. Typicaly it is poor tracking of the belt. Look at the belt area and see if you have belt dust. if you do that is your answer.

If not it can be belt tension. I suspect they have a specification for belt tension. I would have to see the belt pully layout to make a resonable quess. Without that it is only a quess say 1/2 inch deflection assuming it is a serpentine belt routing. Best course of action is not to guess, get the spec buy the tool at autozone and do it by the numbers. It is called a deflection meter. it should be cheap.

As a reference, loose belts at high speed tend to have a wobblling sound. Engineers call it "Chordal action". Tight belts have a high pictched wine.

I assume you put in the correct bearings. as an example you did not replace high speed needle bearing with unground comercial bearing without seals etc. The wrong bearing at high speed can cause a hollow sound. Typicaly because the bearing is not the correct unit and can not take the load or it is loose by design and well it wobbles. i assume you bought the proper bearing or cross refrenced th Italian make with a suitable alternative. There are dozens of bearing design categories maybe more. if we get a poster at this forum who works for a bearing company he will say thousands, point is there is a bunch and it matters.

I wish I could help more.

Good luck to you.

Lee

 

I had a similar sound when I replaced my belts. Turned out to be the rear bank timing belt metal cover was vibrating enough to make a tone. It was a result of the timing belt slipping off a cog. The engine also idled poorly and was louder in general.

 

I won't speculate on what you are hearing (you've had a few guesses already), but a good alternative to a stethescope is a lenght of garden hose (or heater hose, fuel hose, etc. about the diameter of a garden hose). Hold one end to your ear and use the other to poke around in the engine bay. It will focus what you are hearing and can help you pinpoint where the sound is coming from. If it is something loose, like a shield, if you press the hose against it, the noise will go away or change.

 

'hollow' generally implies something's resonating, echoing, or both. Altho, have heard a sound that might be described that way when the edge of a belt was rubbing against something that would vibrate. Kind of a violin string effect.

Unlikely to be a bearing, they 'moan', or 'whine', & eventually rattle.

 

This gentleman has a thought that sounds like a possibility.

It seems like you did the right thing on bearings and such.

Belts if aligned improperly can dust in a hour or so of operation. This of course depends on the base material.

I will be curious on what you find.

Good luck.

Lee

 

Just a few more ideas-

To try and answer your question on belt tension: How did you set the tension for the timing belts? The spring in the bearing mount needs to be functioning correctly during install to get correct tension. With the bearing unlocked (not tightened down), it will move in and out as the engine is turned by hand. You want to lock them down when the spring is applying the maximum tension. If you applied any pressure to the loose bearing during install that was beyond the spring applied tension (which you never want to do), than the belt could be too tight.

I think your idea of taking components out of the mix (alternator, wp, AC) one at a time and running the car for a VERY short while could be helpful.
I would do this first, before looking into the timing belts/tensioners. Maybe it's just a tight or loose water pump belt?

Also- it's normal for the new belt to leave some black markings on the new tensioner bearing. See the attached of a timing belt run for maybe 20 miles, and even then there were black marks on the tensioner bearing pulley. You can also see how we used a large socket and washer to clamp down the black fiberglass dust cover so we could run (but not drive!!) the car with the front cover removed.

good luck- jwise
Image Unavailable, Please Login

 

My apologies for being so vague. The rear exhaust cam skipped one tooth off somehow. I took the belt off, replaced it with a new belt, and timed the cams back to correct spec.

 

Recheck your timing marks. If one cam is a tooth off it will run but will sound "off".