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Q: My son bought an S10. It drove for a week. It was good until I changed oil and heard a knock!

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Truck ran fine for week.changed oil started knocking.i went to listen pulled plug wires one at time,no difference.still good oil psi. doesnt sound like anything(knock) ive heard son revs truck knock seems to come and go almost go away!i research 4.3 found several issues with balance shaft.found TSB gm repair bulletin tensioner kit to install on 96-03 4.3.i cross ref every gm pt number found aftermarket kit available.jump gun didnt further diagnose engine my bad as im fairly good wrench.tore front of engine down,t-chain very worn.could cause balance shaft noise/knock?pull engine up to get oil pan off btw the oil was black sludge(fresh oil only a day ran)and oil filter was seized?took 3 hours to get off.no rods loose on crank little side to side.i installed tensioner kit the chain was single roller per gm cross ref 12458911. but looked chincy. any ideas on the knock in case we start up and its still there?we put in hv oil pump in case guage was wrong and check rockers too. Checked flex plated and torqued conv bolts, h balancer everything external i could think of.pushed down on rocker for collapsed lifters,no bent p rods,took long pry bar couldn't find play in pistons.all be it they were hard to get to the engine was still in truck.

My car has 190000 miles.
My car has an automatic transmission.

Hi there. I hate to be the bearer of bad news, I but I think you will need to pull the engine out, disassemble it, and check clearances precisely to determine the source. Given your mileage, and the "sludge" condition you found, worn timing gear set, etc., there are multiple wear conditions that likely exist, and a rebuild or engine replacement is the solution. Most often, when an engine "knocks when you rev it" as you describe, the connecting rod bearings have excessive clearance between the crankshaft bearing journal and the connecting rod bearing (not side-to-side as you mention). If you would like to have a professional inspect the engine knock in person for a second opinion, a certified technician from YourMechanic can come to your location to do so.

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