Evinrude 4906B 4HP 1969 Owner's Manual page 63

3-22 POWERHEAD
cylinder, the piston pushes the connecting
rod with tremendous force, and this force is
transferred to the connecting rod journal.
Since there is little
crankshaft, it bounces away from the con-
necting rod. The crankshaft
immobile for a split second, until the piston
travel causes the connecting rod to catch up
to the waiting crankshaft
mers it.
In some instances,
crankpin bore becomes highly polished.
While the engine is running, a "whirr"
and/ or "chirp" sound may be heard when the
engine is accelerated
speed to about 1500 rpm, then quickly re-
turned to idle. If chatter
ered, the crankshaft and the connecting rods
should be replaced.
Inspect the bearing surface
and rod cap for signs of uneven wear and
possible overheating.
ly caused by a bent connecting
heating is identified
surface color and is caused by inadequate
lubrication or operating the engine at exces-
sive high rpm.
Inspect the needle bearings, if installed.
A bluish color indicates the bearing became
very hot and the complete
MUST be replaced, no question.
Service the connecting
faces according to the following procedures
and precautions:
a- Align the etched marks on the knob
side of the connecting
marks on the connecting rod cap.
b- Tighten the connecting
taching bolts securely.
Installing the rod cap
cleaning the inside surface.
kept with its matching rod.
or no load on the
then remains
journal, then ham-
the connecting
rapidly from idle
marks are discov-
of the rod
Uneven wear is usual-
rod. Over-
as a bluish bearing
set for the rod
rod bearing sur-
rod with the etched
rod cap at-
onto in
the rod preparation for
The cap MUST always
rod
Rod cap separated slightly
Notice the matching hills and valleys.
c- Use ONLY crocus
bearing surface at the crankshaft
connecting
of abrasive cloth.
d- Insert the crocus cloth in a slotted
3/8" diameter
drill press and operate
speed and at the same time, keep the con-
necting rod at a 90
shaft.
e- Clean
enough to remove marks.
once the marks have disappeared.
Clean the piston pin end of the con-
f-
necting rod using the method described
Steps d and e, but using 320 grit Carborun-
dum cloth instead of crocus cloth.
g- Thoroughly wash the connecting
to remove
check the bearing surfaces a second time.
h- If the
cleaned properly, it should be replaced.
i- Lubricate
connecting rods with light-weight
vent corrosion.
PISTON AND RING
INSPECTION
Inspect each piston for evidence of scor-
ing, cracks,
pin boss, or worn pin boss.
Testing the
be
installation.
from its matching
cloth
rod. NEVER use any other type
shaft. Chuck the shaft in a
the press at high
0
angle to the slotted
the connecting
DO NOT continue
abrasive grit. After
connecting rod
the bearing surfaces of the
AND SERVICE
metal damage, cracked
Be especially
of
wrist pin end the
rod.
to clean
end of the
rod ONLY
in
rods
washing,
cannot be
oil to pre-
piston
to
rod prior