Engine knock/rattle noise

[quicksilver]

This noise just developed not too long ago. I have been letting the car sit for winter, so it's been getting minimal driving miles, but I have been starting it up every other week to operating temp.

Back in December I changed the valve cover gaskets and the oil pan gasket since one, or all, of them were leaking, changed oil (obviously) and ran it for a bit, then parked it. While doing this, I meticulously cleaned the gasket mating surface on the heads for the valve covers, vacuumed as I was moving along and even blasted everything out with air after I was done. Then the oil pan was dropped and that whole area was cleaned. I'm 100% sure nothing foreign got down there that shouldn't have been there, I even blasted out the oil pickup screen (low pressure air) and dislodged some carbon build up from there.


Since its been so warm here lately in NY, I have been able to drive the car around, upon startup, I'd get some very light ticking that would go away after warming up for a short time. I wouldn't hear anything at all while driving at any engine rpm, but randomly while coasting from 40 to 25 mph (engine rpms hit 1,000), I would hear a rattle sound that would go away as soon as I tap the throttle. That went on for a week or exactly under those conditions.

Now once the car is fully warmed up, the sound will range in how loud it can be, and i hear it mainly when in park. Sometimes it can sound really loud to the point I can hear it inside my garage while the car is idling outside, all door closed on the garage. While driving, it does sound like it is prevalent from time to time yet not so loud at all, and it still comes and goes while coasting.

Sounds like it's coming from the trans bell housing, but I can't be too sure about that just yet, thought it does seem to orignate fRon the driver side. There are times while in park that I can't hear the noise while standing above the engine, then if kneel down by the driver side tire I can hear it.

Oil pressure appears to be fine according to the gauge in the car, holds a steady 45 psi at idle while cool and will drop to about 25 at operating temp. Once I Rev it, the pressure rises up to 45 psi again. It never fluctuates randomly.

I also have done a ton of searching into this, hoping that it's not rod knock bit maybe a stuck lifter, or potentially a busted HB? I've even seen a thread where the TC was suspect to be the cause. Pretty soon I'm going to pull it into the garage to dig further into, but if it seems to be rod knock, I see this car going bye bye pretty *dang* soon. Having too many issues with this car to make it worthwhile to even keep and drive.

If you fellas have any other advise to offer, or see that I'm overlooking something, please let me know, cause right about now I'd lIke nothing better than to set up 20lbs of tannerite inside the car and set it off (been dealing with a bunch of vehicle issues lately).

[quicksilver]

Another note, LIM gaskets were replaced before I purchased the car, which was roughly 20k miles ago. Never had any knocking of any kind until now.

[unclebubbaSE]

Just an idea....I had the same symptoms that you are describing, after the engine had warmed up, especially in park or neutral, there was an inconsistant clatter/knockng type noise that would dissapear when I blipped the throttle, or when accelerating, noise was never present when cold. My problem turned out to be caused by worn rod bearngs. After changing out the bearings and obviously adding fresh mobil 1, the noise is absolutley gone!. Depending on your mileage, I don't think it would hurt to drop the oil pan again and check the bearings and crankshaft for signs of wear.

Just a thought, good luck!.

[quicksilver]

Yea, it's definitely rod bearings, or something of that sort. Drained the oil and had a yellowish color come out right away, but only a tiny bit, but it ran like oil and not sludge-like when water gets in there. Ran oil down my finger, had purple rubber goes on, and I could see metal particulate in there.

I already put some Lucas in there with no change, so I just tried the easiest out and it still knocks.

Next I'll see if I can get a trade in on it. If that doesn't work, guess I'll pull an engine and go from there, maybe make a private sale and drive it until it's sold.

[irish91983]

I was a having slimier problem. Mine ended being my harmonic balancer. At start up would be fine but once it would come down in rpms it would start to make the noise. It was pretty loud. I would inspect it and see if any of the rubber is torn on the balancer.

[quicksilver]

Well, I went and checked that, rubber is not torn, but it seems likes it might be loose almost, ie I can turn the SC pulley a few degrees by hand, and want the crank pulley move as well, but not the solid piece behind the ribbing, that also turns while the engine is on....

[quicksilver]

Also, the engine vibrates ever so slightly, and the knocking sound is coming from the passenger side of the engine. Standing up top since the car is on the ground, I can put a long rod on the motor mount on the pass side and hear the knock/rattle the loudest. I've checked at multiple points along the block, even on the trans bell jousing, and I hear nothing else.

[quicksilver]

I PULLED the belts off the engine, ran it, the noise is still there. I also checked the harmonic balancer to see if I can move it at all with my hand. I was probably able to move it ~1/4" total, probably 1/8" either way from center. So what's normal for movement on one of these?

[quicksilver]

I PULLED the belts off the engine, ran it, the noise is still there. I also checked the harmonic balancer to see if I can move it at all with my hand. I was probably able to move it ~1/4" total, probably 1/8" either way from center. So what's normal for movement on one of these?

Anybody got any idea on this?

[MKMike]

Well, I went and checked that, rubber is not torn, but it seems likes it might be loose almost, ie I can turn the SC pulley a few degrees by hand, and want the crank pulley move as well, but not the solid piece behind the ribbing, that also turns while the engine is on....

No personal experience on this, so what follows is my opinion, FWIW.
Just from a logical standpoint, if different parts of the harmonic balancer remain stationary while other parts move, then it seems like the balancer is bad.
I know it was a common problem on previous generation Bonnevilles.
As this generation ages, maybe it will be common with these, too.