Evinrude 4906B 4HP 1969, Owner'S Manual

Page: 65 / 422

3-24 POWERHEAD
Check the piston ring grooves for wear,
burns, distortion or loose locating pins.
During an overhaul, the rings should be
replaced to ensure lasting repair and proper
engine performance after the work has been
completed.
Clean the piston dome, ring grooves and
the piston skirt. Clean the piston skirt with
a crocus doth.
Clean carbon deposits from the top of
the piston using a soft wire brush, carbon
removal solution, or by sand blasting. If a
wire brush is used, TAKE CARE not to burr
or round machined edges.
Wear a pair of good gloves for protection
against sharp edges, and dean the piston
ring grooves using the recessed end of the
proper broken ring as a tool. NEVER use a
rectangular ring to clean the groove for a
tapered ring, or use a tapered ring to clean
the groove for a rectangular ring.
NEVER use an automotive-type ring
groove cleaner to clean piston ring grooves,
because this type of tool could loosen the
piston ring locating pins. TAKE CARE not
to burr or round the machined edges.
In-
spect the piston ring locating pins to be sure
they are tight. There is one locating pin in
each ring groove. If one locating pin is
loose, the piston must be replaced. Never
attempt to replace the pin, it is NEVER
successful.
Oversize Pistons and Rings
Scored cylinder blocks can be saved for
further service by reboring and installing
Cleaning the piston ring grooves. An automotive
type ring groove cleaner should NEVER
be
used.
Using
a
micrometer
to
check the roundness
of
the
piston.
oversize pistons and piston. rings. ONE
MORE WORD: Oversize pistons and rings
are not available for all engines. At the
time of this printing, the sizes listed in the
Appendix were available. Check with the
parts department at your local dealer for
the model engine you are servicing, and to
be sure the factory has not deleted a size
from their stock.
ASSEMBLING
CRITICAL WORDS
Two conditions absolutely MUST exist
when the piston and rod assembly are instal-
led into the cylinder block.
The slanted side of the piston must face
toward the exhaust side of the cylinder.
The hole in the rod near the wrist pin
opening and at the lower end of the rod
must face UPWARD.
An automotive ring compressor should
NEVER
be
used
to
install the rings for
a
two-cycle engine.