The main malfunctions of the timing mechanism (timing gear) are:
violation of thermal valve clearances (on engines with adjustable clearance);
wear of bearings, cams of a camshaft;
malfunction of hydro-compensators (in engines with automatic clearance adjustment);
Decrease in elasticity and breakage of valve springs;
wear and lengthening of camshaft drive chain (belt);
wear of camshaft drive pulley;
Wear of oil slinger caps, valve pins, guide sleeves;
fouling of the valves.
The following causes of failure of the timing system can be identified (they are basically the same as the causes of crank mechanism failure). But before that, read about what documents do you need to scrap a car.
exhaustion of the established engine resource and, as a consequence, high wear of structural elements;
engine abuse, including the use of low-quality (liquid), contaminated oil, the use of gasoline with high tar content, prolonged engine operation at excessive revolutions.
The most serious malfunction of the timing mechanism is the so called valve hang-up, which may lead to serious engine damage. There are two reasons for this malfunction. The use of low-quality gasoline, accompanied by tar deposits on the valve stems. The other cause is resonance, weakening or breakage of valve springs. In this case, when the piston reaches the top dead center, the valve does not have time to sit in the “seat”. Fortunately, this malfunction on modern cars is quite rare.
It is necessary to say separately about the faults of hydro-compensators. At use of liquid or strongly polluted oil, hydro-compensator stops fulfilling its basic function, namely, to compensate automatically a gap in timing. Further operation of the engine may lead to seizure of expansion joints.
Thermal gap violation on engines with adjustable clearance can occur due to wear of the bearings and cams of the camshaft, wear of the camshaft drive pulley, as well as due to improper adjustment.
Faults in the timing system are quite difficult to diagnose, since similar external signs may correspond to several faults. Often, a specific malfunction is established by direct inspection of the timing components with the removal of the cylinder head cover.
Most timing faults result in timing errors that cause the engine to become unstable and fail to deliver its rated power.