Many parts of the valve train have the responsibility of timing the opening and closing of the valves. They all work in conjunction with each other, dictated by the rotation of the camshaft. Two types of valve lifters work off the camshaft rotation to open and close the valves: the solid adjustable type, and the more commonly used hydraulic lifter. They both need oil supplied by the oil pump to operate effectively. When valve lifters begin to wear, the valve can not open and close precisely and several symptoms of the problem will appear.
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Instrument Warning Lights
The first symptom of a bad lifter will likely show up on the instrument panel as an oil light that stays on or flickers periodically. The oil passages in the head and camshaft become clogged, restricting the flow of oil, which leads to low or inadequate oil pressure in the top of the engine, or valve train. The oil light might come on during engine warm-up and disappear when the engine has reached normal operating temperature. A bad lifter can cause this condition even when the oil pump functions properly, or the oil level in the crankcase reads full.
Clicking Engine Noises.
Valve lifters that have worn excessively will produce a noise that originates rom the top of the engine under the valve covers or directly under the intake manifold. The first signs will be a clicking noise that appears during engine warm-up, or during a time of cold or freezing temperatures. Cold temperatures break down the viscosity of the oil and it looses its lubricating qualities. The lifters sit at one of the highest points of the engine, making it difficult for thick oil to travel upwards, causing a clicking or moderate ticking noise.
Clacking Engine Noises
When lifters have worn excessively, or if they have loosened from adjustment (solid type lifters), they will emit a harsh clacking sound during engine warm-up and continue to produce the sound during all driving ranges. The engine oil light might come on during warm-up and stay on during all driving conditions, regardless of weather. There might be a noticeable miss or stumble in the engine. If the miss has a constant rhythmic pattern, it means that the lifter has collapsed and can no longer open and close the valve. Exhaust emissions might appear as white-grey smoke, or even black smoke.
Excessive Valve Lash
Excessive vale lash will be detectable between the rocker arm tappet and the top of the valve spring face, when the valve covers have been removed. The adjusting nuts can back off of the rocker arms, due to wear or stripping, producing excess clearance. Some hydraulic lifters can be readjusted for "zero" lash to seat the lifter. The solid type lifters will also show excess clearance between the valve spring face and the rocker arm tappet. The solid lifters can be adjusted with a feeler gauge to remove excess clearance. Lifters that continue to clack after proper adjustment have worn too much.
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