GMC 1982 Light Duty Truck, Service Manual, Page: 730 / 1435

6A7-2 6.2 DIESEL
the bottom side or pan rail of the engine.
The lubricating system of this engine is a pressure feed
type which means that a pump forces oil through the
galleries to the necessary parts. The pump is mounted to the
bottom side of the rear main bearing cap. Extending down
from the pump and into the oil is a pick-up tube with a
screen cover to filter out foreign material. Oil is picked up by
this tube and pumped through the oil pump. The pump is a
gear type which uses 2 meshing gears. As these gears rotate
in opposite directions, the spaces between the gear teeth and
the housing fill with oil from the inlet side of the pump. Then
as the teeth mesh, the oil is forced out through the outlet
tube. The pump is driven from the engine camshaft by
means of an intermediate shaft. The oil is next pumped
through a cooler located in the radiator which cools the oil
and thus helps to remove engine heat.
From the cooler the oil passes through a filter. This
filter is a cartridge type and all oil going to the engine passes
through this filter. The cartridge is made of materials that
trap foreign m aterial to prevent it getting to engine
components. If this fuel flow filter becomes clogged, the
engine is equipped with a by-pass valve which is spring
loaded. This valve protects the engine from oil starvation by
opening when increased pump pressure tries to pump oil
through a clogged filter. When the pressure causes the by­
pass valve to open, the oil by-passes the filter and the engine
continues to receive lubrication. Replacement of the filter at
proper intervals will prevent damage to the engine due to a
clogged filter.
From the filter the oil is pumped through the drilled
galleries in the case to the various moving metal parts in the
engine. The rear crankshaft bearing is fed by a hole drilled
from the rear main bearing bore to main gallery. Oil is
pumped further through the main gallery to a drilled oil
gallery which has been drilled the full length of the left side
of the case. Oil from this gallery feeds the camshaft bearings
and a second gallery which runs the full length of the right
side of the case. All other engine components are provided
lubrication by these 2 oil galleries. Holes are drilled from
camshaft bore to crankshaft bore to provide oil for main
bearings # 1 through # 4 . Lifters on the right side receive
oil from the right side main oil gallery and lifters on the left
side receive oil from the left side oil gallery. The lifters
contain a disc valve which meters oil to the hollow push rods
and to the rocker arm and valve stem in the cylinder head.
After a small accumulation of oil is in the head, it begins to
drain back to the crankcase. As mentioned before, the first
four main bearings receive oil from vertical holes drilled
from the cam bores to crank bores. Oil flows onto the
crankshaft main bearings and provides lubrication for the
crankshaft to rotate freely in its bearings. As the crankshaft
rotates, it slings oil off the crankpins to cover cylinder walls,
pistons, piston pin and piston rings. Oil drains off these parts
and back to the engine.
There is also a second by-pass valve. This is the oil
cooler by-pass valve. It works much the same as the oil filter
by-pass valve and opens to allow an alternate route for the
oil if the cooler should become clogged.
There is an oil pressure switch which is assembled to
the top rear of the cylinder case to sense oil pressure in the
main gallery.
C O M P R E S S IO N TEST
To determine if the valves or rings are the cause of low
com pression, a test should be made to determ ine the
cylinder compression pressure.
When checking compression, the batteries should be at
or near full charge. The lowest reading cylinder should not
be less that 70 percent of the highest and no cylinder reading
should be less that 275 p.s.i. (1900 kPa).
1. Remove air cleaner.
2. Disconnect the wire from the fuel solenoid terminal of
the injection pump.
3. Disconnect wires from glow plugs then remove all glow
plugs.
4. Screw the compression gage J-26999-10 into the glow
plug hole of the cylinder that is being checked.
5. Crank engine.
This should be done with six "puffs" per cylinder.
Normal-Compression builds up quickly and evenly to
specified compression on each cylinder.
Piston Rings Leaking-Compression low on first stroke
tends to build up on following strokes but does not
reach normal.
N O T IC E : Do not add oil to any cylinder to compression
test as extensive damage may result.
O N VEHICLE SERVICE
E N G IN E M O U N T S
Engine mounts (Figures 6A7-1 and 6A7-2) are the
nonadjustable type and seldom require service. Broken or
deteriorated mounts should be replaced im m ediately,
because of the added strain placed on other mounts and
drive line components.
Checking Engine M ounts
Raise the engine to remove weight from the mounts
and to place a slight tension in the rubber. Observe mounts
while raising engine.
If a powertrain mount exhibits:
a. Hard rubber surface covered with heat check cracks;
b. Rubber separated from a metal plate of the mount;
or
c. Rubber split through center.
R eplace the mount. If there is relative movement
between a metal plate of the mount and its attaching points,
lower the engine on the mounts and tighten the screws or
nuts attaching the mount to the engine, frame, or bracket.
Front M ount R e p lace m e n t
1. Rem ove mount retaining bolt from below frame
mounting bracket.
2. Raise front of engine and remove m ount-to-engine
bolts and remove mount. Raise engine only enough for
sufficient clearance.
3. Replace mount to engine and lower engine into place.
4. Install retaining bolt and torque all bolts to
specifications.
Rear M ount R e p lace m e n t
1. Support engine weight to relieve rear mounts.
2. Remove crossmember-to-mount bolts.