1985-1998 [Subscribe to Daily Digest] |
Testing and Inspection
NOISY VALVE OPERATION - CAUSES AND RECTIFICATION
Valve chatter after car has been parked for longer than 48 hours.
During a period of prolonged parking, oil drains out of the high-pressure chambers in the cam followers, allowing air to get in. For a period of about 15 minutes after the engine has been started, valve chatter will be heard until the air has been purged from the cam followers.
The engine speed should not be allowed to exceed 3,000 rpm until the noise has ceased.
See also item 4 below.
Valve chatter on starting the engine after an oil change.
If the noise from the valves did not occur before the oil change, the noise will disappear of its own accord as soon as the oil in the engine has reached normal working pressure.
Temporary noise on starting a cold engine.
This noise is perfectly normal and will disappear of its own accord as soon as the oil in the engine has reached normal working pressure.
Valve chatter on starting after work on the car that has involved cranking the engine by hand or on the starter motor.
The noise is due to one or more of the cam followers having been drained of oil and will therefore disappear after the engine has been running for a while. At worst, it may take 15 minutes at between 2000 and 3000 rpm for the noise to disappear. At lower engine speeds, it will obviously take considerably longer to expel the air. Do not run the engine at a speed greater than 3,000 rpm as this may damage the cam followers.
Noise after fitting new cam followers.
The cause and rectification are the same as under item 4 above.
Noise occurring after a short period of idling with a hot engine (hot oil).
If the engine is run at 1500 rpm or more, the noise will disappear after a while.
The noise is due to low oil pressure in the hydraulic cam followers when the engine is idling. Check the oil feed pipe, connectors and O-rings for leaks.
Noise occurring at high engine speeds and disappearing after the engine has been at idling speed for a time (the period required can vary considerably).
This noise is due to an excessive amount of air in the oil at high engine speeds. The ingress of air is caused by leakage on the suction side of the oil pump, a poorly sealing O-ring in the inlet pipe or a leak in the inlet pipe caused, for instance, bye porous weld.
Noise from an individual cam follower regardless of how the car is driven.
The most likely cause is that a piece of dirt has become trapped in the check valve in one (or more) of the cam followers. The best way to identify a defective cam follower is to switch off the engine, remove the camshaft cover and use a screwdriver to depress the cam followers. A light or spongy feel indicates a defective cam follower.
NOTE: Replace any defective cam followers.
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