Q: 2001 Pontiac grand Prix 3.1l engine tapping

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2001 Pontiac grand Prix engine starting tapping. About a month later I noticed coolant disappearing. A couple of weeks later I found coolant in the oil. Pulled the engine and tore it apart and found the intake manifold gasket failed on 4 ports. All the hydraulic lifters had collapsed, the crank and camshaft had damage (grooving) due to the leak. Completely pulled everything apart, had the block vatted and new camshaft bearings installed at NAPA. Rebuilt the engine replacing everything except the pistons, connecting rods, valves (did replace seals), valve springs and fuel injectors. Also replaced temp sensor, crankshaft position sensors, fuel pressure regulator, vacuum lines, coolant hoses, spark plugs and wires. Put everything back together filled with oil and coolant. Starts and runs but it still has the same tapping as before the leak. I checked the valves and springs when replacing the valve stem seals and they were good. Tapping is loud enough to hear inside the car. Help?

My car has 120000 miles.
My car has an automatic transmission.

Hi there. Typically an engine tapping noise is caused by either cylinder head lifters that are loose or worn out, rockers and valves not properly adjusted, a timing belt or timing chain that is loose or crankshaft / cam out of alignment or not balanced correctly. Oil restriction problems are also a leading reason for this type of problem. The problem with an overheating issue is that is can cause a lot of internal damage, especially when coolant mixes with the engine oil. An engine knock can also be produced by an ignition timing problem or misfire, which is also common after an overheating issue, especially if you didn’t replace the electrical wiring to sensors or fuel injectors as well.

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