Yanmar 1GM User Manual page 57

Sacrificial
anode
OPERATION, LUBRICATIO N, MAINTENANCE A"' D T UNE- UP
5 1
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sacrificial
~
anode
su re. Th e ree d va lve closes w he n the pis ton mo ves up in
the cy linder. Th is creates a negative pressure in the crank-
case. which hel ps the piston rings sea l agai nst the cy linder
bore. A hole in the brea ther chamber routes oil bac k 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 roc ke r ann cove r. A
labyrinth system separates oil from the cra nkcase gas. See
Ftgure 16. A hole in the breather chamber routes oil back
into the engi ne. how ever. excessive oil will pass into the
breather tube to the inta ke po rt or intake man ifo ld.
On 3HM and 311 M35 mod el s. a me sh assembly on top
of the roc ker ann cove r se parates oil from the crankcase
gases. See Fig ure 17. A breather tube routes the crank-
case gase s to the intake ma nifold.
A ntico r rosio n :\I ai ntenance
Th e engines are eq uipped w ith sacri ficial an odes that
provide protection against galvanic corrosion. Sacrificial
anodes are re lativel y ine xpensive and easi ly replaceable
components that pro vide adequate corrosion protec tion in
most situations wh ere light-to-moderate corros ion condi-
tions exist. Anodes arc made ofa highly activ e zinc allo y.
Check the condition of the ano des periodical ly and fre-
quently. Replace any anode that is corroded to 50 percen t
of its original size.
Engine mod els IG M and IG MI D are equipped w ith a
si ngle sacrificial anode that is attached to a plate located
on the cy linder bloc k (f'iJ=: u re 18). A thread ed type sacnfi-
cial anode is used on 2G M, 2G M20. 3G M. 3G M30. 3 HM
and 3HM35 mod el eng ines. O ne anode is located in the
cy linde r hea d (Figu re 19), and one anode is located in the
cy linder block on 2G M and 2G M20 mod el engines ( f' i g~
ure 20). while two anodes are located in the cylinder
block on 3GM. 3G M30. 3H M and 3HM35 model en-
gmes.
Proceed as follo ws to se rvice the sacrificial anodes:
I GM an d I GMI Omodels
I. Drain the cooling sys tem.