Knocking noise coming from 1987 350 engine.

[Chuck Step-a-side]

Worked all weekend replacing the engine wiring harness with decent older wiring and it went fairly well. I got everything hooked up and went for test drive for about 10 miles and then stopped for gas. After filling the tank and starting the truck, I heard loud knocking sound that sounded like a loud valve rocker hitting or an exhaust leak. On my return home the truck ran with no issues other than the knocking. I put it in park and let it idle for 10 more minutes while I try to located the knocking and then shut the truck off. I don’t see any oil leak or oil in the anti-freeze and don’t know what else to check. How do I find out if this is a broken valve, lifter, crank shaft or something else that’s gone bad? Thanks

1984 Chevy Stepside with 1987- 350, 4 bbl and 350 A/T, 2 wheel drive

[bd]

Did you check the oil level?  Did you notice any associated changes in oil pressure?  Pick up a 3' long, thick-wall rubber hose that has about 1-1/4" ID.  Use it like a stethoscope to help locate the origin of noises.  The rubber wall of the tube will dampen and reject ambient sounds coming in from the sides.  The method works better than most alternatives.

[Chuck Step-a-side]

Worked all weekend replacing the engine wiring harness with decent older wiring and it went fairly well. I got everything hooked up and went for test drive for about 10 miles and then stopped for gas. After filling the tank and starting the truck, I heard loud knocking sound that sounded like a loud valve rocker hitting or an exhaust leak. On my return home the truck ran with no issues other than the knocking. I put it in park and let it idle for 10 more minutes while I try to located the knocking and then shut the truck off. I don’t see any oil leak or oil in the anti-freeze and don’t know what else to check. How do I find out if this is a broken valve, lifter, crank shaft or something else that’s gone bad? Thanks

1984 Chevy Stepside with 1987- 350, 4 bbl and 350 A/T, 2 wheel drive

I found out the knocking was a very loose valve. Tighten that valve and no more knocking.