I just picked up an '02 Lq4 motor last night in the blistering cold (yes it' was -1 degree out) and the guy who sold it to me said they took it out of the truck because it had what sounded like a main bearing knock. The engine has 225k on it and they were driving it around with the knock for awhile before putting in a replacement motor. The engine had 40psi of oil pressure at hot idle and the guy said it definatly WAS NOT a rod knock but sounded like a main bearing. I never heard the motor run myself but my question to you guys is how the hell could this thing have a main bearing knock, have good oil pressure and survived being driven around for a week before swapping the motor out? At any rate, I'll tear it down this spring when it gets into the 40's but can anyone tell me what else would cause a "main bearing knock" sound in one of these things? Oil pump? maybe a collapsed lifter? Something tells me the rotating assembly is fine on this thing and these guys took this motor out for no good reason. Anyways, the oil is even clean, I just can't believe this has a spun bearing in it. For what it's worth this motor came out of an 02 3/4T HD truck with a 4l80. They gave me the engine with the flexplate and spacer still attached to the crank. What's the likelyhood that the flexplate is cracked on it? It was dark and cold out when I picked it up so I didn't get a chance to check to see if it was cracked. Just baffled that's all. Ideas?

 

cut the oil filter open to check for jewelry.

 

Just for some thought, I think my old 4.8 spun a ROD bearing. And i put like 5K miles on that thing, still boosted at 9 lbs afterwards. I havent torn it down yet, and the assumption of the problem was made by a few different people.. Bronze or copper whatever it is, was in the oil filter.

 

copper color would definitely be a bearing of some sort I would assume. That would be the place to start. I would think you've been around these motors long enough, OP, to make an educated guess based on little things like that.

 

Noo, there's no metal in the oil! That's what I'm saying. What I'm asking is do the oil pumps ever make a "knocking" noise like a bad main bearing or do the roller lifters ever make a knocking noise when they go bad? The sound definatly sounds deep but there's nothing to warrant me thinking it's a bad bearing.

 

When I drained my oil there was only a little metal in it and on the magnet, it wasn't until I cut the filter open that I found bearing material.
https://www.performancetrucks.net/fo...d.php?t=453578

 

Did you have excellent oil pressure as well?

 

Lifter will make a knocking sound if it bleeds down. I wouldn't be surprised if that's what was making the noise, if there's no bearing material in the pan or filter. My 5.3 with 118k on it used to do it every once in awhile. Would start knocking randomly, do it for 30 seconds or a minute, then go away. Freaked me out the first time it happened.

 

Bad main's squeal, rods knock, oil pumps grind/rattle, lifers tick/grind/slap, pistons slap, wrist pins knock... ohh and bad valves ummm tick.

I just tore down a motor the ticked when pulled, it turned out to be two bent valves. Those in turn took out two lifters, thus the tick. So you cant take someones word for it or speculate the cause.

 

Cut open the filter Joe, see what you find. If it looks clean, I'll bet that it's just a bad lifter...it's tough to diag without hearing the noise...what one guy calls a "knock" might just be a loud "tick". With 225k I'd still tear it down anyway (as you said you're going to do in the spring)...wish you had a warm place to work so you can tear it down sooner, I'm curious to know what's causing the noise