Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hi, I am Mike, welcome. I'm reviewing your question.
A tap is usually excess lash in the valve train and a lifter tapping because of the extra space. What happened could have been either a collapsed lifter or a bent push rod.
What I would do is before adding some STP or straight 50 weight motor oil to see if it quiets down meaning it is mechanical try to determine which cylinder it is on first by canceling out each cylinder one at a time listening if killing any cylinder causes the noise to change, then remove that valve cover and watch as the engine idles if either of the 2 push rods on that cylinder wobble when they spin. Also you can take a piece of wood 2x4 and press on the side of the rocker while the engine is idling and if the noise changes that lifter is probably collapsed.
No, it is serious cause if the noise begins to get worse something could go really wrong depending on what it is, but like you said connecting rods usually knock when they go bad, I doubt if it's a bent valve cause if it were it would not seat and that would cause a misfire and I don't think piston would make that noise, only maybe a slap.
Other than like I said, I the push rod wobbles, remove it and roll it on a flat surface to double check if it's bent. Pushing on the side of the rocker may check if a collapsed lifter. I would kill the cylinders first to determine which one it is. If you have a scan tool, that might have a option in it for that, if not, there are several ways to do so, one being unhooked each fuel injector wiring is this has an injector on each cylinder. Another which I don't like to do is disconnect each coil on plug primary wires if it's COP.
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