1928 Cadillac - GM Heritage Center

Oil Circulating System
CHAPTER II
Engine Lubrication
The supply of oil is carried in the pressed steel reservoir that covers the
bottom of the crankcase. The oil is circulated by a gear pump attached to
the front main bearing cap inside of the crankcase. The pump is driven by
a vertical shaft which is in turn driven by a spiral gear on the camshaft.
The pump draws oil from the bottom of the reservoir and delivers it under
pressure to the bearings. Oil reaches the front main bearing through a
passage in the bearing cap. A supply pipe from the pump runs the length
of the engine parallel to the crankshaft and leads branch off from it to feed
the center and rear main bearings. From the rear of this pipe the oil is conducted
to the hollow camshaft through which it flows forward and lubricates
the camshaft bearings.
The oil is carried from the front end of the camshaft to the oil pressure
regulator, which is attached to the crankcase just ahead of the right-hand
LUBRICATION' AND CARE 53
cylinder block. The regulator contains a by-pass with metering screw for
adjustment of the oil pressure at idling speeds and a spring controlled valve
that opens to prevent excessive pressure at high speeds. The oil that passes
the regulator, either through the by-pass or around the valve, lubricates the
front end chains.
The valve stems are automatically lubricated by oil sprayed from two
small holes drilled in the wall of each cylinder at such a distance from the
bottom of the cylinder that, when the piston is at the bottom of its stroke,
these holes register with a groove in the piston between the second and third
piston rings. As the piston descends on the power stroke, oil collects in
this groove and as soon as the groove registers with the holes, the pressure
of the gases above the piston forces oil out upon the valve stems. Surplus oil
collecting in the valve compartments is returned to the crankcase through
drain passages.
All oil returns to the oil pan through a fine mesh screen in the pan.
Oil Level
The normal capacity of the oil pan is two gallons, which fill it to the level
of the screen above the pan. When the oil pan contains this amount, the
oil level indicator on the right-hand side of the engine (Fig. 27) indicates
"Full." As the oil level descends, the indicator indicates "Fill" and then
"MT" (Empty). Oil should be added as soon as the indicator ball has
dropped to "Fill." If the indicator has dropped to "NIT" under no circumstances
should the engine be run until oil has been added.
The mileage interval at which oil must be added depends upon individual
circumstances. It is recommended that the oil level indicator be checked every one
hundred to one hundred and fifty miles, although it is improbable that oil will be
required as frequently as this.
Oil Pressure
Figure 27. Showing the location of the oil filler, oil level indicator, oil pan drain plug and
orher lubrication features.
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The pressure of the oil in the supply pipe is indicated by the oil pressure
gauge on the instrument board (Fig. 6).
It is absolutely necessary that there be oil pressure just as soon as the engine
starts and as long as the engine is running. If the oil pressure gauge does not
indicate pressure as soon as the engine starts, stop the engine at once and
investigate the cause. First, check the level of oil in the oil pan. If the level
is above "Fill," consult the nearest Cadillac service station.
The amount of pressure indicated by the gauge depends upon several
things: the kind of oil, the temperature of the oil and the speed of the engine.