Car Problem - Rod Knock on '96 Buick

[MBG]

My daughter has a '96 Buick Park Ave. - 3.8L. We bought it 2-3 years ago. It had 100,000 miles when we got it and currently has about 140,000. Only problem we have previously had is about 6-months ago I had to replace the upper-plastic intake manifold due to a water leak.

Per my daughter, at idle it started to have an intermittent oil pressure light come on. I told her to pull over immediately and I met her to look at the car. I first checked the oil (I just changed it a couple of months ago) and the level was fine. When I started it up I could hear a knock in the engine. Sounds louder from underneath the car especially at increased rpm's. I also verified that the oil pressure was low with the dash mounted gauge.

I changed the oil and removed/disassembled the oil filter. This is the first time I took apart a filter. It had black grit, some small shinny non-magnetic specs, an a couple of metal slivers (maybe 1/32" wide x 1/16"-1/8" long). I wasn't able to heat the car up totally but the oil pressure was around 20-30psi.

Tonight I thought to remove the injector wires one at a time to see which cylinder might be the culprit. The result was unexpected. When I removed one of the wires - the cylinder at the firewall closest to the accessories the noise increased by tenfold (maybe a little exagerrating).

Is this just a rod bearing? Can I get by with just changing the rod bearings? Looks like on this big Buick I can drop the pan and get at the bottom end w/o removing the engine. Due to age/miles don't want to put too many dollars into it.

Thanks,

Mike

[Russianwolf]

Not knowing if that will fix it or not, have you looked into a replacement engine? the 3.8 was a rather popular engine from what I recall, so I'll bet the salvage yards have some realatively low mile replacements for decent prices. If you can get one , the swaps aren't too bad (timewise if you do it ourself, or money wise to hove a shop do it). I bet you could get out with less than a grand and have a 60k mile engine.

the metal slivers are what scares me. likely the ring in one cylinder has a piece of debris and is literally chewing up the wall. If that's the case, you will eventually loose the cylinder and without tearing the whole thing down, you can't fix it.

[MBG]

Not knowing if that will fix it or not, have you looked into a replacement engine? the 3.8 was a rather popular engine from what I recall, so I'll bet the salvage yards have some realatively low mile replacements for decent prices. If you can get one , the swaps aren't too bad (timewise if you do it ourself, or money wise to hove a shop do it). I bet you could get out with less than a grand and have a 60k mile engine.

the metal slivers are what scares me. likely the ring in one cylinder has a piece of debris and is literally chewing up the wall. If that's the case, you will eventually loose the cylinder and without tearing the whole thing down, you can't fix it.

Piecing things together maybe it is a cylinder problem. I did have coolant in the cylinders before I c/o the upper manifold (GM designed the egr tube through the plastic upper manifold housing - heat/time did it in). And she has had problems, at times, starting the engine even though the battery is almost new. Also, when I went to look at the car she couldn't start it. When I got there an hour later it started right up.

[jseklund]

MBG-
I would check out www.bonnevilleclub.com. I personally drive a bonneville with the 3800, but it's a 2003. I have found great info and knowledgeable people on that site for my car. They have a section for "Other 3800 powered cars", and there is a thread by a relatively new member (maybe you?) who has a similar problem:

http://www.bonnevilleclub.com/forum/...ic.php?t=87434

Some of the details are different, and you give some more insite here (ironically) than the person in this thread did on the bonneville site. (Preface- I have a 2003, so my knowledge may be slightly 'off' from your exact model engine)

First- the upper intake manifolds are notorious in our cars. The "lifetime coolant" and plastic intake manifold gasket are a recipe for disaster. It's a ticking time bomb and a good thing that you changed it out. However, if you got a good amount of anti-freeze in your engine, it could have done A LOT of damage. I would imagine that you would have noticed this damage right away though, for the most part.

Second- The oil pressure sender in these cars (at least 2000+) is also a common problem area. You may have a bad pressure sender, and it was going flunky on you. You may want to check the actual pressure with an oil pressure guage and see if they match. If they don't, I would replace the sender.

Third- The rods, from what I've read, work for about 10 seconds when replaced in such instances. Here is a link to someone with a similar problem that may help:

http://www.bonnevilleclub.com/forum/...ight=rod+knock

Let me know how it works out. I hope this helps and that it's not a rod!

[guycox]

Not knowing if that will fix it or not, have you looked into a replacement engine? the 3.8 was a rather popular engine from what I recall, so I'll bet the salvage yards have some realatively low mile replacements for decent prices. If you can get one , the swaps aren't too bad (timewise if you do it ourself, or money wise to hove a shop do it). I bet you could get out with less than a grand and have a 60k mile engine.

the metal slivers are what scares me. likely the ring in one cylinder has a piece of debris and is literally chewing up the wall. If that's the case, you will eventually loose the cylinder and without tearing the whole thing down, you can't fix it.

The silver bits are non-magnetic so it's likely the bearing rather than the ring or a chuks of cylinder.

Unless you have the history on the car. You might try pulling the cap off one of the big ends that' s not knocking and putting some plastigauge on it just on the off chance the crank has been turned ( does any one still do that?)... You'll have to buy a full set of bearings anyway (at least I did the last time I did an overhaul on my 100-6 Healey).

It's a shame that auto manufactuers don't publish the alloy makeup of all their pieces parts like the jet engine folks do - then you could have just run the oil through your local neighborhood spectrum analyzer to see what parts were failing....

[Russianwolf]

The silver bits are non-magnetic so it's likely the bearing rather than the ring or a chuks of cylinder.
...

I think the block on the 3.8 is Alum. if so, it could be any of the above.

This is why I drive a 40 year old truck with a cast iron block.

[Daryl]

My personal experience is that you will be lucky if it is just the bearing. Most likely the bearing has spun and damaged the rod and the crank shaft. Go ahead and drop the pan and take a look. You will need a mic to measure the crank and an inside mic to measure the rod. I bet the journal on the crank is oval now. And it is possible the piston has been cracked too.

[gwyneth]

Don't forget it's always worth checking whether there was a recall, no matter how old the vehicle or how many previous owners. Sometimes we get lucky.

http://www-odi.nhtsa.dot.gov/cars/pr...callsearch.cfm
ODI - Office of Defects Investigation

[guycox]

I think the block on the 3.8 is Alum. if so, it could be any of the above.

This is why I drive a 40 year old truck with a cast iron block.

Good point. But isn't there a cast iron sleeve even with cast iron block?

[MBG]

Good news is it was easy to remove the oil pan and rod caps from below the engine.....as you probably guessed bad news is the rod bearing spun and wore the crankpin down approximately 0.060". I did remove the adjacent rod cap and the crankpin looked great. The bearing showed some wear but nothing I'd call excessive. Although this is the first time I examined bearings this small - at work I have designed the bottom ends of a few locomotive diesels one having an 8" crankpin.

Just wondering w/o signs of damage to the adjacent cylinder what caused this one to fail???

Thanks for the help,

Mike

[Daryl]

Good news is it was easy to remove the oil pan and rod caps from below the engine.....as you probably guessed bad news is the rod bearing spun and wore the crankpin down approximately 0.060". I did remove the adjacent rod cap and the crankpin looked great. The bearing showed some wear but nothing I'd call excessive. Although this is the first time I examined bearings this small - at work I have designed the bottom ends of a few locomotive diesels one having an 8" crankpin.

Just wondering w/o signs of damage to the adjacent cylinder what caused this one to fail???

Thanks for the help,

Mike

Like you say, it had a hunderd thousand on it when you bought it and you probably don't know how it was treated. Lack of oil or contaminated oil would be my guess. Once the bearings wear there is less oil pressure to keep them lubricated. Also if it had an ignition problem with that one cylinder it would probably help to acellerate wear on the bearings.