Rod Bearing vs Main Bearing
 

Hello folks. New to the forum and not terribly familiar with the Chevy 4.3L as I've only owned pre-85 Dodge trucks all my driving days. Anyhow, my uncle has a 96 Blazer with the 4.3TBI (185,000 mi.) that developed a bad knock the other day while I was out with him. We had 30 miles of limping it home to cover but it did make it. Oil pressure was staying down to maybe 10 psi at idle but didn't bottom out all the way. Holds normal 40 psi on steady acceleration. No apparent misfiring or lack of power. Knock is almost certainly coming from the crankcase. I tried pulling plugs one at a time and starting the motor expecting to find that one would quiet the knock somewhat but instead all were consitent sounding except #4 which actually seemed to intensify the knock.
My question then I suppose is - would this likely point to a main bearing failure as opposed to a rod bearing? And also would it be worth trying to drop the pan & cross member to get at the bearings without pulling the engine?
I know it's likely to come to an engine swap with the mileage and all, but I have never had to do much interior engine work and wanted to learn and at least find and verify the failure.
Any help and/or criticism is appreciated...lol

My best advice is pull the motor.....with that kind of mileage u are gonna want to replace the crank with the bearings anyhow, and hell that's a lot of work.....esp. If it's a 4x4 cause of the front diff. I'd say pull it and rebuild or find a good low mileage donor....:icon_mrgreen: this way if u swap the motor out then u can tinker with the old one......

Yep...in the process of pulling it now. Realized oil pan wasn't coming off anyway w/o pulling the motor. Thanks..and will come back with anymore ?'s along the way.

willing to bet its a rod knock. we shall see.

Got her all done. Found a used one w/ 90,000 compete from a wrecked S-10 for $250. She runs great so far and have a bin full of good spare parts. Alot of fun pulling with the limited space and all the gadgets and gizmos.. but not too bad. I'd like to thank the forum in whole for some useful tips I found browsing such as lowering the tranny to get at that those top bell housing bolts with a 3' extension and swivel socket...worked like a charm. I have yet to dig into the old motor..kind of exhausted..lol Will do so soon and let ya know.

you can either lower the tranny or put a hole through he fire wall, others while you have your old motor out do it up so you have a good spare, strip it down and do a bit here and a bit there but do it properly you will learn a lot, and end up with a good motor

I made my engine rod knock. I ended up getting a new engine.

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