the pip mark (if any) toward the top of the piston.
This applies to cast iron pistons (only as shown
above).
Die cast pistons use five (5) narrow rings.
PISTON RINGS
Check fit of piston rings in piston ring grooves.
C h e c k ring gap with rings installed in cylinder
bores. Refer to Fig. 11 for correct gap and groove
clearance.
Figure 10
CRANKSHAFT
Measuring Cylinder Bores
C h e c k crankshaft screw threads, keyways, ta-
PISTONS
pered ends and all machined and ground surfaces
for wear, scores, or damage. Crankshaft journals
Check pistons for scores cracks or enlarged ring
which are out of round more than 0.001" (.0254 mm)
grooves; replace pistons if any of these conditions
must be reground. Bearing inserts are available in
are found. Measure each piston with a micrometer
0.010" (.254 mm), 0.020" (.508 mm), and 0.030"
in relation to the cylinder bore diameter to be sure
( . 7 6 2 ) undersizes for reground crankshafts. Main
the clearance is between 0.002" (.050 mm) minimum
bearing journals must be maintained so bearings
and 0.004" (.101 mm) maximum.
are snug fit. The oil seal ring groove or grooves in
crankshafts fitted with oil seal rings must not be
WRIST PINS
worn. The ring groove walls must have a good finish
and they must be square. Check to be sure the oil
Check fit of wrist pins on pistons and connecting
p a s s a g e s are open and clean through the crank-
rod bushings. Wrist pin should be a light press fit in
shaft.
pistons. If wrist pin is loose fit, the pin, piston, or
both should be replaced. Check fit of wrist pin in
CONNECTING ROD BEARINGS
connecting rod bushing by rocking the piston. This
c l e a r a n c e should not exceed 0.0015" (.038 mm).
Check connecting rod bearings on crankshaft
Replace wrist pin bushings if excessive clearance
journals for proper fit. Used bearing inserts should
is found. Wrist pin bushings should be reamed after
b e replaced. Connecting rod caps are not inter-
being pressed into connecting rods. Replace used
changeable. The locking slots of the connecting rod
wrist pin lock wires.
a n d cap should be positioned adjacent to each
other.
Clearance between the connecting rod journal
and the connecting rod bearing must not be less
than 0.0003" (.007 mm) or more than 0.0021" (.053
mm) after rebuilding.
MAIN BEARINGS
Check for wear or flat spots; if found, bearings
should be replaced. If type with sleeve bearing, this
bearing should be checked for scores and wear and
Figure 11
replaced if necessary.
Piston Ring Positions-Gaps and Groove Clearance
UNLOADER MECHANISM
All rings must be located in their proper ring
Used unloader mechanism should be replaced by
grooves as shown. The rings can be identified by
unloader kit 265015 for Tu-Flo 500 compressors.
the width and should be installed with the bevel or
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