Knock up top?

[iamtherealJayy]

1997 GMC k2500 5.7L
Not my vehicle, just working on it.
After tracing wires and tinkering finally got the truck running but it had an atrocious knock/tick. Requested rockers be tightened, I did so, truck wouldn’t start? Loosened rockers(my choice) around 3/8 of a turn and truck fired right up but it’s knockin hard. Here’s a minute or so clip.

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The knock is very apparent up top, you could feel it in the alternator so I took the belt off, no change, I kept feeling around and you can feel it very well on the intake. Is this engine toast? I can’t tell whether it’s moving same speed as engine or half as fast, it gets worse under load when moving P-R or N-D at idle it’s not noticeable. Slight throttle and it sounds like you’re shaking a rock around in a bowl.
Edit: also fresh oil change with 5w-30 due to prior owner cranking with no spark oil was thin and smelled of fuel. Only 20lbs oil pressure? Could going to say Shell Rotella diesel oil cure some of the knocking? At idle 20, off idle 45-50 up to around 2500 then it stops increasing.

 

[PlayingWithTBI]

I kept feeling around and you can feel it very well on the intake. Is this engine toast? I can’t tell whether it’s moving same speed as engine or half as fast, it gets worse under load when moving P-R or N-D at idle it’s not noticeable. Slight throttle and it sounds like you’re shaking a rock around in a bowl.

Got a stethoscope? You should be able to hear where it's the loudest. Listen from top to bottom, side to side. It could even be the torque converter the way sounds resonate through the engine.

 

[Schurkey]

Broken flexplate (pull cover, look/listen)
Exhaust leak (chuffing sound--look for evidence of broken exhaust manifold or failed donut)
Rod knock (Ground the spark to each cylinder in turn--see if one of them radically changes the knock.)
Failed lifter (pull valve covers, look for lazy or non-moving rocker arm)

Different oil isn't going to fix that.

 

[iamtherealJayy]

I considered the torque converter/ flex plate since it’s sorta delayed? after blipping throttle. The truck does have an exhaust leak at the joint under passenger door. Work on getting that fixed and see if I can narrow down the noises. By grounding the spark? what do you mean how do I go about testing that. I thought about adjusting the valves on the engine running since they’re less noisy now than prior, but didn’t want to risk losing some oil. Owner is being cheap with this truck and I don’t quite blame him it’s got 318k on the dash lol. Plus- it’s got a jasper trans in it atleast.

 

[Rocket Surgeon]

I don't think I am hearing bottom end noise.

my take... bad lifter(s) that can't bleed down are holding intake valves open.

The ones I dealt with were is a 4.3 v6 that had years of neglect. ie., no oil changes. The failure followed reassembly with a new intake gasket. All lifter were coked solid. The lifters always made crap noise prior and quieted when you poured transmission fluid into the oil.

I stuck in a used set from my junkpile (from a 3800, same cross ref part for 4.3) and the truck went another 8 years. Currently to be scrapped by owner because it needs brake pads. Still runs.

If these are roller lifters, you can easily grab and swap in a used set as I had to.


You might even find dumping 1/2 quart in trans fluid in will soften sludged up lifters. if the knock decreases, you lifters are binding on internal sludge.

I think your oil pressure is ok. If in doubt use 10w40 next time.

 

[L31MaxExpress]

I am hearing a spun rod bearing. Cylinder 1 connecting rod perhaps knocking on the soon to be new exit door.

 

[L31MaxExpress]

My suggestion, stop running it now and the block might be salvaged for a rebuild. Pull the oil pan and check all the connecting rods for play.

 

[Hipster]

What I'm hearing sounds like a rod bearing. Pretty far gone at that.

 

[Erik the Awful]

That sounds like rod knock. Pull the inspection cover off the transmission bellhousing and check the flexplate. If it's not broken, pull the motor.

Edit: I just read your other post, and the knock comes and goes with rocker arm adjustment? It might be a lifter, but that's awfully loud.

 

[iamtherealJayy]

I personally don’t think it’s bottom end, it doesn’t increase and decrease with engine rpms correctly enough to correlate bottom end with me. I’ve already sold the owner a 350 vortec block for $100 so all else he’s got a block ready for cleaning and heads up. Owner thinks it’s a bent pushrod and already ordered new ones. The truck only runs when being worked on I’ll take valve covers back off on the next warmer day( high of <40° F next few days) I’m more on the line of a stick lifter. When I originally tightened the rockers it sounded better so I went through and checked them and tightened accordingly(which was clearly too much as I loosened them all 3/8 of a turn) and the knocks back. When the knock came back I mentioned getting some Lucas or some similar additive to see if it’s a worn part or similar issue. The oil pressure isn’t super concerning as my daily driver 1978 k10 gets around 25 psi once warm and I run shell rotella t4 diesel oil in that 350 lol.