CRANKCASEBREATHER
The crankcase breather prevents pressure from building
up the crankcase
It
also prevents oil contamination
by removing moisture or gasoline vapors and other
harmful blow-by materials from the crankcase. These
vapors are routed
to
the carburetor where they are
mixed with incoming air and burned in the combustion
chamber.
A
sticky breather valve can cause oil leaks,
high oil consumption, rough idle, reduced engine power,
and
a
rapid formation of sludge and varnish within the
engine.
Crankcase Breather Service
The crankcase breather does not require servicing.
Replace breather if it’s broken or cracked or
if
crankcase
becomes pressurized as evidenced by
oil
leaks at the
seals or excessive oil
in
the air cleaner housing.
PRESSURE
LUBRICATION
All
engines use an oil pump
to
provide a constant flow of
oil
to
the engine parts. The oil supply collects in the oil
base where
it
is picked up by the oil pump pick-up cup.
A
bypass valve is used
to
control oil pressure. Drain oil
before removing oil base and always use a new gasket
when replacing the oil base.
Oil
Pump
The oil pump is mounted below the gear cover and is
driven by the crankshaft gear.
A
discharge passage in
pump cover registers with a drilled passage
in
the
crankcase. Parallel passages distribute oil
to
the top
and bottom main bearing and the oil bypass valve.
Circumferential grooves in the main bearings supply oil
to
connecting rod bearings through drilled passages
from each main journal.
A
drilled passage connects the
front main bearing oil supply
to
the front camshaft
bearing; rear cam bearing is splash lubricated.
Normal oil pressure should be
8
psi
(55
kPa) or higher at
1500
rpm when the engine is at normal operating
temperature.
If
pressure at
1500
rpm drops below this
value, inspect oil system for faulty components.
Check oil pump thoroughly for worn parts and replace
pump as an assembly
if
parts are worn. Other component
parts (pickup cup, pickup tube, gaskets, etc.) can be
replaced individually. Prime pump by oiling it before
installing.
Oil
Bypass
Check
Ball
The oil bypass check ball is located in the
oil
base.
To
gain access
to
the check ball the oil base cover must be
removed. The check ball limits oil pressure
to
a maxi-
mum
of
about
25
psi
(172
kPa) at normal operating
temperatures
(250°F
oil temperature).
The check ball is non-adjustable and normally does not
need maintenance. Determine
if
check ball is operating
correctly by inspecting as follows (Figure
2):
1.
Remove internal retaining ring.
2.
Remove spring and check ball with a magnetic
tool.
3.
Determine proper operation by checking the spring
and check ball according
to
the following measure-
ments:
Check Ball Diameter.
.....
.0.3125
inch
(7.94
mm)
Spring
Free Length
...............
1.00
inch
(25.4
mm)
Load..
............
.2.6
±
0.2
Ibs
(11.6
±
0.9
N)
when compressed
to
0.5
inch
(12.7
mm)
4.
Check the check ball seat and clean away- any
accumulation of metal particles which could cause
erratic check ball action. Verify the check ball seat is
not damaged.
5.
Clean spring and check ball in parts cleaning
solvent and install.
6.
A
new internal retaining ring must be installed with
the outside edges turned towards the top. Press in
until retaining ring outside edge is
0.13
±
0.01
inch
(3.3
±
.3
mm) from top.
0.13±0.01”
RETAINING RING
(33±.3mm)
OIL
BASE
LS-1102
FIGURE
2.
OIL BYPASS
CHECK
BALL
6-2
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