NOISY HYDRAULIC VALVE LIFTER (Cont.) |
air bubbles.
Dirt In the lifter assembly can prevent the disc valve from seating,
or it may become lodged between the plunger and body surfaces.
In either case, the lifter becomes inop-erative due to failure
to “pump-up,” or because the internal parts are no longer
free to function properly. When dirt is found to be respon-sible
for lifter malfunction, remove the lifter assembly and thoroughly
clean It. Recommended engine oil and filter change intervals should
be followed to minimize lifter prob-lems caused by dirt.
Deposits of gum and varnish cause similar conditions to exist
which may result in lifter malfunc-tion. If these conditions are
found to be present, the lifter should be disassembled and cleaned
in solvent to remove all traces of deposits.
Air bubbles in the lubricating oil, caused by an excessively high
or low oil level, may likewise cause lifter malfunction. A damaged
oil pick-up tube may allow air to be drawn into the lubricating
system.
Check for engine oil aeration as follows
Check the engine oil level to be sure it is within specification
and correct as required. Be sure the
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correct engine oil dipstick is being used.
Operate the engine at approxi-mately 1200 rpm until normal oper-ating temperature is reached. Stop the engine and remove the oil pres-sure sending unit. Install a fitting in this opening with a petcock-type valve that will permit attachment of a 1/4 to 3/8-in, diameter hose of suffi-cient length to direct the oil discharge into the oil flier pipe. Close the valve.
Start the engine and operate it at approximately 500 rpm for a mini-mum of 5 minutes; then, open the valve slightly to permit a steady dis-charge of oil. Check the oil flow.
Increase the engine speed to ap-proximately 1000 rpm and check for air bubbles in the oil. To facilitate checking for air bubbles, direct the oil flow over white paper or through a piece of transparent tube. The engine should not be operated at excessive speeds or for extended periods with the oil bleed attached.
If oil aeration is evident, remove the oil pan for further test and/or inspection of the oil pump intake system. Perform corrective action as required to remove air from the lubricating oil.
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