First I`ll say hello and thanks . I have a 90 Bronc 4+4 XLT . Its a 351W with a E4OD . Motor is close to 195,000 , trans was rebuilt July 2004 for $3200 .

I noticed a slight knocking sound 6 months or so ago . It was during warmup and went away at operating temp . I thought it sounded like a lifter bouncing on a cam lobe . Thats just to give a description of the sound and it was mild , more like a strong tick at that point . I did the usual , change oil , looked around for anything obvious .

Well as it would be , the sound became a constant ( at start and all temps ) and prominant to the point of concern . It is a strong mechanical , hard metal to hard metal ( not tinny or ringy ) . It has a tight snappy tone .

I used a stethescope and believe the sound comes from the bottom . It has the ability to sound top end also . I mean it is loud enough to resonate .

I have good oil pressure , no metal or shiny whatsoever in the oil pan . The motor runs fine with no hesitation or stalls , no indication of engine trouble . Compression checked out fine and the plugs only looked mildly rich . I did a power drop test and found no change at all . I looked for cracks in the exhaust manifold as best I could , nothing .

So now I think trans . I pull the thing out to look at the flywheel . I can`t see any cracks that are obvious . I`m out of ideas . The trans had a 1 year warranty that expired last July .

Anyhow , the noise is RPM paced and is there at idle and under load . Any help would be greatly appreciated .

 

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Okay, official business out of the way, let's get to the meat of the matter.
It doesn't sound like bearing noise to me, that usually changes under load and no-load conditions. It sounds more like an interference problem. Did you look carefully at the ring gear and starter teeth? The bolts that hold the tq. converter to the flexplate? (One might be loose and is rubbing against the block plate)

I am always concerened about the timing set in higher mileage engines, not that it would usually make a noise like you describe and still produce the engine performance you're experiencing, but that fiber cam gear is not known for longevity.
Just a thought...

 

I concur with TigerDan. Sounds like bearings to me also.

 

Hmm, I don't think you read my post too closely. I said it doesn't sound like bearings to me

But I'd be interested in knowing what the oil pressure actually reads, if your reading is coming from the stock gauge which is really just an idiot light with a needle which gives a normal reading at anything above about 7 psi, or a real mechanical gauge.

 

ooops. You are right. I didn't read it too closely. Still sounds like bearings with knocking coming from the engine though. They might be worn and checking with an oil pressure guage will help determine if they are. I could be wrong, but... with the engine at 195K I think it is a good chance that they are worn.

 

I get a tapping in the lifters on start but it goes away after oil starts flowing. Anyhow I notice a constant low knock that to me sounds like the bearings but I cant hear it when I rev because the exauhst is too loud so I dont think the motor was balanced properly on rebuild causing worn bearings and low oil pressure. So my point is that I would consider bearings seriously, other than that I noticed that stock manifolds on the passenger side like leak due to not being able to get in there and tighten the bolts very well, so it might be a manifold leak your hearing.

 

Well here`s an update . I could not see any flaws on the flywheel . Today I took the converter to the shop it came from and they will send it out to be evaluated on the manufacturers machine . There were no indications of bolts interfering with the engine plate , nor the bellhouse . Nothing has been obvious so far but I`ll keep at it .

 

I hear that the endplay of the crank could make the noise I have . Worn out thrust .

 

It's possible, but an automatic doesn't get near the wear on the thrusts that a stick does, since there's no pressure applied from using the clutch.

Easy enough to check crank endplay with the motor still in the car though...