ENGINE BEARINGS LUBRICATION
RELATION OF ENGINE LUBRICATION TO THE LIFE OF THE BEARINGS
A Modern Engine Lubrication Method
An example of an engine with a force feed or pressure lubrication
system, where crankshaft is drilled and where oil passes through
the crankshaft to the camshaft, through drilled passages in the
crankcase is the Oldsmobile six, series "D." This engine
has three main bearings and three camshaft bearings, and the gear
type oil pump is mounted in elevated location.
The oil which seeps out of the camshaft bearings, main bearings
and connecting-rod bearings is whipped into a vapor which floats
throughout the engine, depositing a film upon such parts as cylinder
walls, pistons, piston pins, valve lifters, and valve stems. The
quantity of oil in the oil reservoir is indicated by a depth rod
on the left side of the crankcase.
sei
Fig. 30. Oldsmobile six, series "D" forced-feed
engine oiling system with an elevated pump and through camshaft bearings.
Near the end of suction line is a ball check valve in this line
(leading from 2). This is for the purpose of keeping the oil line
primed at all times where the elevated type pump is used.
For example, in turning corners or when the oil has been drained
out of the system, preparatory to refilling, it will be retained
in the pipe line.
Tracing the course of the oil: An elevated gear type oil pump (1)
is attached to the front end of the engine on the timing gear cover,
and is driven by a projection of the camshaft extending through
this cover.
The pump draws oil from a pocket or depression in the center of
the oil reservoir (2) by means of a pipe (3) on the outside of
the engine and forces it into the camshaft (4), which is drilled
hollow to the front journal.
At this point, the oil passes out of the camshaft into an annular
groove around the journal which coincides with a hole drilled in
the crankcase (5) for conveying the oil to the front crankshaft
main bearing, (5A).
From this point the oil may follow either of two courses, into
the hollow crankshaft (6), or into the oil pipe (7), leading from
the front bearing cap to the center (8) and rear bearing (9).
A portion of the oil is thrown out at the crank pins to lubricate
the connecting-rod bearings. (On earlier jobs a hollow cam-shaft
formed the auxiliary oil passage to the center and rear main bearings.)
From the center (8) and rear bearings (9), the oil passes up through
drilled passages (10, 11), in the crankcase to the center (12)
and rear (13) camshaft bearings.
The oil-pressure indicator gauge (14) on the instrument board registers
its pressure from the supply furnished the rear camshaft bearing
(13) which is the farthest point in the system from the oil pump
(1). This assures one of oil pressure in all points of the line
if pressure is shown on the instrument board gauge.
Midway between the camshaft and crankshaft in this oil passage
is a by-pass channel (15) for the purpose of relieving the oiling
system of any excessive quantities of oil (also leads to the front-end
drive chain).
This by-pass is normally closed by means of a ball and spring,
the tension of which is regulated by a screw projecting' ,o the
channel at the front left-hand side of the engine. Ad.l:aonal tension
on this spring will cause an increase of oil pressure in the system.
Decrease of tension on the spring will elm e
decrease in pressure.
When the engine is warm and supplied with fresh oil, the pressure
as indicated by the gauge should not be less than one pound for
each mile per hour on high gear at low car speeds.
Any excessive drop in oil pressure would tend to indicate thinning
of the oil or an extremely loose bearing in the engine.
The regulating screw for adjusting the pressure should not be reset
to raise the oil pressure when either of these conditions exists,
but the oil should be changed or the bearings taken up, which will
correct the difficulty.
To Obtain Long Life of Bearings Use
Plenty of Good Oil
No amount of oil under-pressure will successfully take care of
metal which has been worn away, but will only soften the noise
emanating from such worn parts for a time; and if the oil has become
extremely thin, the continued use of it will prove but a detriment
to the engine.
A systematic examination and cleaning of the oil reservoir and
screen is of prime importance, and the smooth performance of the
engine will more than repay the time it takes.
Replace the oil in the oil reservoir (2) every 500 miles under
average conditions. While the engine is new the oil should be changed
after the first 250 miles. After being well worked in, it will
be necessary to change the oil at 500-mile intervals, except in
cold weather. In cold weather, when the car is in short trip service,
a lighter oil should be used, and changed at intervals of 300 miles.
The reason for this, in some detail is as follows: Commercial gasoline
is continuously decreasing in volatility. The heat units continue
to be as high as formerly, but the fuel does not vaporize so readily.
The carburetor therefore becomes an atomizer instead of a vaporizer,
and the fuel becomes a fog of minute particles of gasoline mixed
with air, instead of a true dry gas. This condition has led engineers
to adopt several different means of heating the mixture so as to
change the fuel mixture to a gas. On the Oldsmobile engine the "exhaust-heated" intake
manifold is used.
Heat helps a great deal, but there is usually a portion of the
charge which enters the cylinders in a semi-liquid state and therefore
does not burn completely. This portion is of course greater in
winter than summer, but is present at all times.
The surplus or unburned portion of the fuel condenses on the cylinder
and piston heads and finally seeps into the crank case. It not
only cuts the oil seal from the pistons and rings, but dilutes
the crankcase oil, destroying its lubricating qualities. Oil in
this condition is black in color, very thin, harsh to the feel,
and has an offensive odor.
Another reason why the oil should be drained frequently is the
presence of water in the products of combustion. The percentage
of water formed depends upon the proportion of gasoline to air;
a rich mixture or a large percentage of fuel to air will form more
water than a lean mixture. In summer this water vapor passes out
with the exhaust, but in winter it enters the crank case and condenses.
Its presence there is a menace to the engine, because it either
freezes in the oil pipes, causing burned bearings before the heat
of the engine melts it, or it forms an emulsion, a thick pasty
substance which clogs the filter and oil pipes, with the same bad
results.
To drain the oil from the crank case, it is best to work from the
right side of the car. With a suitable wrench, the drain plug can
be removed from the bottom of the oil pan. A bucket should be available,
in which to receive the oil when the plug is removed.
For cleaning, the best method is to remove the oil pan.
Under ordinary circumstances the check valve at the lower end of
the oil pump suction pipe will retain a sufficient amount of oil
to prime the pump when the engine is started, however, if, after
the oil has been replaced and the engine started, the gauge on
the instrument board fails to register pressure, it is an indication
that the oil pump has lost its "prime." Stop engine at
once, remove the plug from the fitting on the oil pipe at top of
oil pump, and pour into the hole a quantity of oil, sufficient
to fill pump body. Replace plug and start the engine.
Fig. 31. The importance of renewing the engine oil often is shown
in these two illustrations. The crankshaft bearing on the left
was ruined by being run less than 1,200 miles without proper lubrication.
The one on the right had been in an engine which was properly lubricated
for more than 32,000 miles and is still good for several thousand
miles more. (From Pontiac instruction book.)
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