better to replace the entire gauge unit than attempt
or replace it. Most often the pump is replaced with a
repairs.
new or factory rebuilt pump.
Persistent low-pressure readings or a zero reading
To replace the oil pump, it is first necessary to
could point to trouble in the oil pump. While a
determine its location and method of drive. The pump
complete failure of the oil pump is rare, any wear of its
may be located either in the oil pan or outside on the
moving parts is likely to impair its efficiency.
lower part of the crankcase, and driven either directly
by the camshaft or indirectly via the distributor shaft.
High-pressure readings may be observed while the
Those driven indirectly from the distributor shaft are
engine is warming up in cold weather, before the oil
easily replaced regardless or their location. The
has reached operating temperature. After a brief
directly driven pumps, on the other hand, pose a
warm-up period, the gauge indicator should return to
problem, since they usually drive the distributor. The
normal. A persistent high-pressure reading points to
procedure for removing and replacing a pump of this
the possibility of a clogged oil line or a poorly
type is outlined in the vehicle's maintenance manuals.
operating pressure relief valve.
The quickest way to find out how an engine's pump is
driven is to check the manual. The next best and most
Servicing Oil Lines, Fittings, and Strainers
expedient method is to lift the distributor and look at its
shaft. If it has a gear, it drives the pump, and removal of
Oil lines and fittings must be maintained so as to
the pump will not affect timing. On the other hand, if it
prevent leakage and loss of oil pressure. Where lines
has a slot or driving lug instead of a gear, it is driven by
are leaking at connections, you can make corrections
the pump shaft. The general procedure in the latter
by tightening the fittings or couplings. Be sure to use
case is to remove the distributor cap and crank the
two wrenches as with fuel lines. Leaks in a line,
engine until the rotor is aimed at the No. 1 cylinder.
whether flexible or rigid, require replacement of the
l i n e . L i n e s s h ow i n g ev i d e n c e o f c r a c k s o r
Align the timing marks (flywheel or crankshaft front
deterioration should also be replaced.
pulley). Then proceed with the removal of the oil
pump.
It is essential that the oil strainer be kept clean to
permit free flow of oil to the pump. The need for
In replacing the pump, simply index its drive gear
cleaning is sometimes indicated by lowered oil
so that the clutch or driving lug on the distributor and
pressure. When cleaning a strainer, you should note
pump shafts will align and mesh without movement of
any deposits, since they may furnish valuable clues as
the distributor shaft (or at least with a minimum of
to the engine condition. Metal bearing particles, for
movement). If it moves, the ignition must be re-timed.
example, indicate deterioration of some bearing or
Under no circumstances should you ever drive or force
journal. To service the strainer, remove the oil pan;
an oil pump into or out of place. Instead, find out what
clean the fine-mesh bronze strainer by using solvent
is holding it; a safety pin or burr on a casting are the
and a brush, and then dry with compressed air. If the
most frequent causes. Also, when replacing either the
screen is damaged, it must be replaced. In the case of
gear or rotary pump, you should always fill the
the floating-type strainer, you should also make sure it
pumping chamber with oil. The pumps need that oil to
is not binding.
effect a positive seal and to prime them. A new gasket
should be used and the retaining screws tightened as
Oil Pump and Relief Valve
specified.
Cleaning and adjusting is all that is usually
Service on oil pumps and most relief valves is
required on the relief valve, although some types are
rather limited, since they are relatively trouble free. An
nonadjustable. A relief valve is cleaned to prevent or to
oil pump will often still be operating effectively when
cure sticking. The plunger or valve must be free to
the vehicle is ready for salvage. Thus, when low oil
move one way or the other under pressure from the oil
pressure or lack of oil pressure develops, you should
or spring. A relief valve may be adjusted in one of two
not immediately assume that the pump is at fault. More
ways. It may be done with an adjusting screw (having a
commonly, the trouble is caused by an inaccurate or
jam or locknut), which either adds or relieves pressure
inoperative oil pressure gauge, oil of too low viscosity,
on the spring, or it may be done by adding or removing
high engine operating temperatures, cracked or
shims or by replacing the spring with one of a different
clogged lines or screens, or a malfunctioning relief
strength. In either case, you should follow the
valve. However, where the oil pump is found to be at
fault, it will be necessary to remove it and either repair
manufacturer's recommendations.
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