car valve chatter only at startup

 ENGINE KNOCKING ON START UP THEN GOES AWAY.

Valve train noise, is usually due to excessive clearance, between two internal engine parts.

Each valve utilizes, a valve spring that returns it to its, original closed position.

So, If a valve spring has broken or a camshaft lobe is worn down; it will cause the engine to create a tapping or clicking sound, due to the excess clearance.

Valve train noise, is similar to a clicking sound of a, sewing machine. The sound frequency of the valve train noise is, one-half the crankshaft speed.

A clicking lifter is one, very common, valve train noise. Also, if the engine is equipped with solid (mechanical) lifters fixing this usually requires, an adjustment.

This type of noise is usually caused by malfunctioning valve lifters or an exhaust manifold leak. If the noise lasts for more than a minute and completely disappears or dimishes after the engine is warm, the most likely cause is an exhaust manifold leak. If the noise only lasts for a few seconds, the most likely cause is a valve lifter malfunction. You should start your diagnosis with a visual inspection of the exhaust system. Inspect the exhaust manifolds for leaking gaskets or cracks. Black soot marks where the manifold mates to the cylinder head are key indicators of an exhaust manifold gasket leak. Inspect for broken exhaust manifold bolts. Inspect the gasket area where the manifold bolts to the exhaust pipe. Small exhaust leaks can often self seal once the metal engine parts are heated and expanded.

If there are no signs of an exhaust leak and the noise dissipates a few seconds after starting the vehicle, you should suspect an oil control or valve lifter malfunction. Hydraulic valve lifters use the engines oil pressure to expand the lifter which provides a zero valve lash clearance. This prevents the valves from tapping. When the engine is shut off, a valve and spring in the lifter keep it expanded and retain the oil within the lifter. If the valve or spring allows the oil to drain from the lifter, it will collapse. Upon start up, the lifter will take a few moments to “pump up” and expand as the oil pressure builds in the engine. During this time, the valves may tap since there is clearance between the rocker arm and lifter.

CORRECTIVE ACTION

Replacement of the valve lifters usually requires major disassembly of the engine. There are oil additives available that can free sticking lifters. This type of additive should be added as per the products recommendation. Frequent oil changes with additional treatments may be necessary in severe cases. If these products are an unsuccessful remedy, lifter replacement may be the only alternative. You should consider having the diagnosis verified prior to undertaking any major engine repair.

PRECAUTIONS, TIPS, and NOTES

The exhaust system becomes very hot. Use caution when working around hot or moving engine parts. Prior to removing any exhuast system fasteners, you should spray them with a penetrating lubricant. This will aid in the disassembly of the nuts and bolts and reduce the risk of breakage.

When the sound is throughout the entire valve train the cause is usually; the weight of the oil or the oil supply itself. Too much oil in the crankcase will cause, foaming and aeration. When air gets into the lifters, they will fail to operate properly. Insufficient oil supply to the lifters can also cause, general valve train noise.

Conclusion

So, as a mechanic you hear the phrase “my engine is making a strange noise” relatively often. Though there are many possible causes, the valve lifter, is often the source of the noise.