Lubrication
is used to:
• prevent contact between metal surfaces
• reduce friction, wear and heat
• remove
foreign agents (metal shavings etc) which might otherwise damage parts
Components
of a lubricating system for an inboard marine engine include:
• oil pump
• sump
• suction strainer
• dipstick
• filter
• cooler
• temperature gauge
• pressure gauge
• relief valves
Lubrication System
(Courtesy: Caterpillar)
Oil is drawn from the sump
through a suction strainer by the oil pump which is driven by either the camshaft
or crankshaft. The oil is pumped to the engine circuit. A pressure relief valve is fitted, which
will open when the pressure in the circuit exceeds the recommended pressure.
This can happen when oil is cold. As the oil heats up, the pressure reduces
and the valve closes to maintain recommended pressure.
Oil at the recommended pressure
is pumped to the cooler which maintains a constant temperature by using sea
water to draw out heat. Oil then passes through a filter to remove small foreign
particles before it enters the engine. Some filters are fitted with relief
valves which open to allow oil into the engine if the filter becomes blocked.
Most filters are of a disposable type and must be replaced at regular intervals
as specified by the manufacturer.
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Cut Away of a Caterpillar Oil Cooler
Some oil cooling units are
directly housed with the engine heat exchanger.
Temperature and pressure
gauges are fitted between the oil cooler and the engine for monitoring purposes.
Oil moves into the engine
through a pipe which runs the length of the engine with distribution pipes
to each main bearing. Alternatively, oil might be fed to the main bearings
by galleries cast in the block. This lubricates the main bearings and the
oil then flows through to lubricate the bottom or big end journal. Oil then
flows up a hole inside the connecting rod to lubricate the gudgeon
pin or little end at the piston.
Excess oil from here helps
lubricate the piston rings. Oil and vapour from the sides of the revolving
bottom end bearing are thrown onto the cylinder liner and onto the underside
of the piston lubricating the gudgeon pin and piston
rings. In smaller engines, there is no hole drilled in the connecting rod
and relies on the oil thrown from the bottom end bearing.
Camshafts, driving gears
and valve gears are lubricated in a similar manner i.e. galleries and pipes
to maintain lubrication at all metal to metal contact parts.
Some manufacturers cause
the oil to flow from an open pipe onto the underside of the piston as an additional
means of piston cooling.
The oil return to the sump
is by gravity through drain holes and open galleries.
Ranger Hope © 2005 (contains
reworked material courtesy of ANTA)