Rod Knock 1996 Buick Park Ave. - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-17-2007, 01:31 PM   #1
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Default Rod Knock 1996 Buick Park Ave.

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'*. 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
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Old 10-17-2007, 02:49 PM   #2
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On this one you will be fighting fire with fire..

Mine was doing this... Ignore the intake... But listen close and you'll know what the sound is... And it was a tight start


The bearing had spun, ate up both the crank and the rod..



If your case is anything like this you will not be able to replace the bearings... They will fail in short order..

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Old 10-17-2007, 02:56 PM   #3
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Quote:
Originally Posted by jr's3800
On this one you will be fighting fire with fire..

Mine was doing this... Ignore the intake... But listen close and you'll know what the sound is... And it was a tight start


The bearing had spun, ate up both the crank and the rod..



If your case is anything like this you will not be able to replace the bearings... They will fail in short order..
So my next step is to look at the condition of the rod/crank?

My thinking is if either is damaged - time to look for a new/used car.


Mike
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Old 10-17-2007, 03:01 PM   #4
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Yes check the crank, see if it has spun a bearing.. If it has the rod could be a bit on the damaged side.. If thats the cars it will be cheaper to find another motor..

Or another car like you stated

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Old 10-18-2007, 12:07 AM   #5
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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
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Old 10-18-2007, 01:16 AM   #6
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Most likely, it was related to the UIM failure and collent getting in the oil. I've seen it before where usually 4-10 months after the UIM is changed, a bearing spins. Sometimes it'* cause it went too long before being diagnosed, or there was some residual coolent that didn't get changed out with the initial oil change.
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Old 10-18-2007, 11:24 AM   #7
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Quote:
Originally Posted by JimmyFloyd
Most likely, it was related to the UIM failure and collent getting in the oil. I've seen it before where usually 4-10 months after the UIM is changed, a bearing spins. Sometimes it'* cause it went too long before being diagnosed, or there was some residual coolent that didn't get changed out with the initial oil change.
I totally agree. Just for kicks I went to look on e-bay at engines.:

1) a guy was selling a new upper manifold air plenum that he didn't get to use since he developed a rod knock before he got it.

2) someone was selling an engine for parts - same story, he replaced the plenum and a couple months later got a rod knock.

I thought I caught my coolant leak early. No signs of coolant in the oil and I c/o the oil twice after the plenum replacement.

Mike
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