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ENGINES---6-CYLINDER
9-1 7
scuffing, scoring or scratches. Usually a few strokes
will clean up a bore and maintain the required limits.
(2) Deglazing of the cylinder walls may be done us-
ing a cylinder surfacing hone, Tool C-3501, equipped
with 280 grit stones (C-3501-3801). If the cylinder
bore is straight and round 20-60 strokes depending
on the bore condition will be sufficient to provide a
satisfactory surface. Inspect cylinder walls after each
20 strokes. Use honing oil C-3501-3880 or a light hon-
ing oil available from a major oil distributor. Do not
use engine or transmission oil, mineral spirits or ker-
osene.
(3) Honing should be done by moving the hone up
and down fast enough to get a cross-hatch pattern.
When hone marks intercept at 60°, the cross hatch
angle is most satisfactory for proper seating of the
rings. (See Fig. 3 1 ) .
(4) After honing,
it
is necessary that the block be
cleaned again to remove all traces of abrasives.
CAUTION:
Be sure all abrasives are removed from
engine parts after honing. It i s recommended that
a solution of soap and water
be
used with a brush
and the parts then thoroughly dried. The bore can
be
considered clean when it can be wiped clean
with a white cloth and cloth remains clean. Oil
bores after cleaning to prevent rusting.
PISTONS
The pistons are cam ground
so
that the diameter
at the pin boss is less than its diameter across the
thrust face. This allows for expansion under normal
I " %
'ROSS-HATCH PATTERN
~
\
F
5 4
^rQ
Fig. 31-Cross
Hatch Pattern
.024 TO .031 IN. LESS
r T H A N DIAMETER AT ( C ) l
THE ELLIPTICAL SHAPE OF
THE PISTON SKIRT SHOULD
B E .008 TO .010 IN. LESS AT
DIAMETER (A) THAN ACROSS
ETER (B). MEASUREMENT
IS MADE
'/e
IN. BELOW
LOWER RING GROOVE
NY221B
Fig. 32-Piston
Measurements
DIAMETERS AT (C) AND (D)
CAN B E EQUAL OR DIAMETER
AT (D) CAN B E .0015 IN.
GREATER THAN
(C)
THE THRUST FACES AT DIAM-
operating conditions. The expansion forces the pin
bosses away from each other, and the piston assumes
a more round shape. Inspect pistons for taper and
elliptical shape before they are fitted into the cylinder
bores. (See Fig. 3 2 ) .
Finished Pistons
All pistons are machined to the same weight in
grams, regardless of oversize to maintain piston bal-
ance. For cylinder bores which have been honed or
rebored, all service pistons include pins and are avail-
able in standard and the following oversizes: .005,
.020,
.040
inch.
Fitting Pistons
The piston and cylinder wall must be clean and
dry. The specified clearance between the piston and
the cylinder wall is .0005 to .0015 inch.
(1) Pistons and cylinder bores should be measured
at normal room temperature, 70 degrees
F.
(2) Measure the piston diameter at the top of the
skirt 90 degrees to the piston pin axis.
(3) Measure the cylinder bores halfway down the
cylinder bore and transverse to the engine crankshaft
center line.
Fitting Rings
(1) Measure the piston ring gap about two inches
from the bottom of the cylinder bore in which it is
to be fitted. (An inverted piston can be used to push
the rings down to insure positioning rings squarely
in the cylinder wall).
(2)
Insert the feeler stock in gap. The ring gap
should be .010 to
.047
inch for compression rings and
.015 to .062 inch for the oil ring steel rails in standard
size bores. Maximum gap in .005 inch
o/s
bores
should be .060 inch for compression rings and .070
inch for oil ring steel rails.
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