Sacrificial
anode
OPERATION, LUBRICATION, MAINTENANCE A"' D TUNE-UP 51
3
~
~
~
~
~fr::
jj
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sacrificial
~
anode
sure. The reed valve closes when the piston moves up in
the cylinder. Th is creates a negative pressure in the crank-
case. which helps the piston rings seal against the cylin
der
bore. A hole in the breather chamber routes oil back to the
crankcase; however, excessive oil will pass through the
connecting lube into the intake port.
On 2GM. 2GM20,
3G~
and
3G
~30
models. the
crankcase breather is located on the rocker a
nn
cover. A
labyrinth system separates oil from the crankcase gas. See
Ft
gur
e 16. A hole in the breat
her
chamber routes oil back
into the engi ne. however. excessive oil will pass into the
breather tube to the intake port
or
intake manifold.
On 3HM and 3
11
M35 models. a mesh assembly on top
of the rocker
ann
cover separates oil from the crankcase
gases. See Fig
ure
17. A breather tube routes the crank-
case gases to the intake manifold.
Anticor
ros
ion :\Iai nten
an
ce
The engines are equipped with sacrificial anodes that
provide protection against galvanic corrosion. S
acr
ificial
an
ode
s are relatively inexpensive and easily replaceable
components that provide adequate corrosion protection in
most situations where light-to-moderate corrosion condi-
tions exist.
Anod
es arc made
of
a highly activ e zinc alloy.
Check the condition
of
the anodes periodically and fre-
quently. Replace any anode that is corroded to 50 percent
of
its original size.
Engine models IGM and IGMI Dare equipped with a
single sacrificial anode that is attached to a plate located
on the cylinder block
(f'i
J=:
ure 18). A threaded type
sacnfi-
cial an
ode
is used on 2GM, 2GM20. 3GM. 3GM30. 3HM
and 3HM35 model engines. One anode is located in the
cylinder head
(Figure 19), and
one
anode is located in the
cylin
der
bl
ock
on 2G M and 2G M20 model engines
( f'
i
g
~
ur
e 20). while
two
anodes
are located in the cylinder
block
on
3GM
. 3GM30. 3HM and 3HM35 model en-
gmes.
Proceed as follows to service the sacrificial anodes:
I
GM
and I
GMI
Omodels
I. Drain the cooling system.
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