TYPES OF LUBRICATING (OIL)
Now that you
are familiar with the lubricating system components, you are ready to study the different
systems that circulate oil through the engine. The systems used to circulate oil are known
as splash, combination splash force feed, force feed, and full force-feed.
The splash system is no longer used in automotive engines. It is widely used in small
four-cycle engines for lawn mowers, outboard marine operation, and so on.
In the splash
lubricating system (fig. 6-29),
oil is splashed up from the oil pan or oil trays in the lower part of the crankcase. The
oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve
mechanisms, piston pins, cylinder walls, and piston rings.
In the engine,
dippers on the connecting-rod bearing caps enter the oil pan with each crankshaft
revolution to produce the oil splash. A passage is drilled in each connecting rod from the
dipper to the bearing to ensure lubrication.
This system is
too uncertain for automotive applications. One reason is that the level of oil in the
crankcase will vary greatly the amount of lubrication received by the engine. A high level
results in excess lubrication and oil consumption and a slightly low level results in
inadequate lubrication and failure of the engine.
Splash and Force Feed
In a combination splash and force feed (fig. 6-30),
oil is delivered to some parts by means of splashing and other parts through oil passages
under pressure from the oil pump.
The oil from
the pump enters the oil galleries. From the oil galleries, it flows to the main bearings
and camshaft bearings. The main bearings have oil-feed holes or grooves that feed oil into
drilled passages in the crankshaft. The oil flows through these passages to the connecting
rod bearings. From there, on some engines, it flows through holes drilled in the
connecting rods to the piston-pin bearings.
are lubricated by splashing oil thrown off from the connecting-rod bearings. Some engines
use small troughs under each connecting rod that are kept full by small nozzles which
deliver oil under pressure from the oil pump. These oil nozzles deliver an increasingly
heavy stream as speed increases.
At very high
speeds these oil streams are powerful enough to strike the dippers directly. This causes a
much heavier splash so that adequate lubrication of the pistons and the connecting-rod
bearings is provided at higher speeds.
combination system is used on an overhead valve engine, the upper valve train is
lubricated by pressure from the pump.
A somewhat more complete pressurization of lubrication is achieved in the force-feed
lubrication system (fig. 6-31).
Oil is forced by the oil pump from the crankcase to the main bearings and the camshaft
bearings. Unlike the combination system the connecting-rod bearings are also fed oil under
pressure from the pump.
are drilled in the crankshaft to lead oil to the connecting-rodbearings. The passages
deliver oil from the main bearing journals to the rod bearing journals. In some engines,
these opening are holes that line up once for every crankshaft revolution. In other
engines, there are annular grooves in the main bearings through which oil can feed
constantly into the hole in the crankshaft.
pressurized oil that lubricates the connecting-rod bearings goes on to lubricate the
pistons and walls by squirting out through strategically drilled holes. This lubrication
system is used in virtually all engines that are equipped with semifloating piston pins.
In a full force-feed lubrication system (fig. 6-32),
the main bearings, rod bearings, camshaft bearings, and the complete valve mechanism are
lubricated by oil under pressure. In addition, the full force-feed lubrication system
provides lubrication under pressure to the pistons and the piston pins. This is
accomplished by holes drilled the length of the connecting rod, creating an oil passage
from the connecting rod bearing
to the piston
pin bearing. This passage not only feeds the piston pin bearings but also provides
lubrication for the pistons and cylinder walls. This system is used in virtually all
engines that are equipped with full-floating piston pins.