PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 2
very heavy (high viscosity). The viscosity of the oil used in gasoline engines
generally ranges from SAE 5 (arctic use) to SAE 60 (desert use). It should be
noted that the SAE number of the oil has nothing to do with the quality of the oil.
The viscosity number of the oil is determined by heating the oil to a predetermined
temperature and allowing it to flow through a precisely sized orifice while
measuring the rate of flow. The faster an oil flows, the lower the viscosity. The
testing device is called a viscosimeter. Any oil that meets SAE low temperature
requirements will be followed by the letter W. An example would be SAE 10W.
(3) Multiweight Oils. Multiweight oils are manufactured to be used in most
climates because they meet the requirements of a light oil in cold temperatures and
a heavy oil in hot temperatures. Their viscosity rating will contain two numbers.
An example of this would be 10W30. An oil with a viscosity rating of 10W30 would
be as thin as a 10Wweight oil at 0 F (17.7 C) and as thick as a 30weight oil
at 210 F (99 C).
(4) Detergent Oils. Detergent oils contain additives that help keep the engine
clean by preventing the formation of sludge and gum. All SE and SF oils are
detergent oils.
4.
a. General. Oil pumps are mounted either inside or outside of the crankcase,
depending on the design of the engine. They are usually mounted so that they can
be driven by a worm or spiral gear directly from the camshaft. Oil pumps generally
are of the gear or the rotor type.
b. RotorType Oil Pump (figure 51 on the following page). The rotor oil pump
makes use of an inner rotor with lobes that match similarly shaped depressions in
the outer rotor. Figure 51 shows the manner in which the two rotors fit together.
The inner rotor is off center from the outer rotor. The inner rotor is driven and,
as it rotates, it carries the outer rotor around with it. The outer rotor floats
freely in the pump body. As the two rotors turn, the openings between them are
filled with oil. This oil is then forced out from between the rotors as the inner
rotor lobes enter the
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