ENGINE MAKES TAPPING NOISE WHEN STARTED
by Mark Davidson
The engine emits a tapping noise on start up. The noise may dissipate immediately after start up or may be present for several minutes.
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.
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.
gave up on sports when the Browns left Cleveland and now spends his
Sundays working under a shade tree in the back yard tuning his son’s
soap box derby car.)