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Connecting rod bearings, '02 3.8 w/95K miles


Reatta Man
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So, my '02 PA with a Series II 3.8 blew the harmonic balancer. Replaced it, and now have a knocking connecting rod bearing.

I already have the parts, and when the weather warms a little, will drop the pan and replace the connecting rod bearings. My question is, has any one else done this with good results?

I parked the car within 20-30 miles after hearing the harmonic balancer start to knock. I don't know if the oil pressure dropped; the sensor is bad and constantly reads something ridiculous, like 150 PSI, even if the engine isn't running.

I replaced a badly worn connecting rod bearing on an older Series I engine, with good results. But this is my first time to deal with a bad CR bearing in a Series II engine. A local mechanic told me that if the bearing is knocking, the crankshaft may be bent, or their could be an oil pump problem. I'm hoping the out-of-synch harmonic balancer caused a vibration and threw the crank out enough to wear out the bearing, but not do any other major damage.

I think the engine is pretty solid; I just drove it to Texas from Florida a few weeks ago, with no noises or problems.

Thoughts?

Joe

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From a chart on main bearing life I saw at the V-6 engine plant, on a tour of the facility in 1988, at the BCA National Meet . . . the balance shaft 3800 has main bearing life (in proving ground miles) of about 90K, compared to the earlier non-balance shaft motors 15K miles. Getting basic vibrations out of the motor certainly helped, it appears.

When I was selling the balancers to customers for the 3800 V-6, there were no later calls to inquire about bearings. This leads me to suspect that the bearing failure was probably not related to the balancer issue.

Unless you've measured the particular bearings, if you already have bearings, there's a good chance they'll not be the size you need. PLUS, the end of the connecting rod with the failed bearing might need to be replaced, TOO. Reconditioned rods should be available.

Considering the motor has that many miles on it, which really isn't that much (all things considered), you might be better off to get a "crank kit" (a crank turned to, usually, .010/.010, to true it up and also provide a fresh wear surface for new appropriately-size bearings) and be done with it. If one rod bearing was having an issue, others might be getting ready to do the same, so doing the crank kit deal might be the best in the long run . . . plus a recon conecting rod, too. Once a bearing has "spun" inside of the big end of the connecting rod, "the circle" and related "bearing crush when installed" have been compromised enough that using that existing connecting rod is a really BIG gamble. Considering how things are to work on on fwd cars, "gambles" are not needed.

Just some thoughts,

NTX5467

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Yeah, I am hoping to find standard-sized bearings, which will tell me they haven't been touched before. As for whether the crank is out of round, I'm hoping that good ol' forged steel crank will take a little excess beating and still be OK. Had the same thing happen to a V-6 Olds version of the Northstar and had to replace the motor. THAT motor was so bad, I almost thing GM intentionally designed problems into it!

The knock is a very light knock, so if the CR bearing only wore through a few thousands of an inch of metal, well, I am keeping my fingers crossed.....

I'll keep you posted.

Joe

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