TRUCK SERVICE MANUAL
BREAKS-AIR
Pistons
of wrist pin to connecting rod bushing should not exceed
Inspect pistons for scores, cracks or damage. If
. 0015". If excessive clearance is apparent, replace
scores or cracks are found, replace the piston. Check
wrist pin bushing in connecting rod. Wrist pin bushings
each piston with a micrometer, Fig. 7, in relation to the
should be reamed after being pressed in place. Discard
cylinder bore diameter to be sure the proper clearance is
all used wrist pin lock wires and replace with new.
obtained as outlined in the specifications.
Connecting Rod Bearings
Inspect connecting rod bearings for proper fit on
crankshaft journals. Also check connecting rod bearings
for wear. If worn, cracked, or broken, the inserts must
be replaced.
Connecting rod caps are not
interchangeable. Position the caps so that the two
locking slots are both located adjacent to the same
capscrew.
Refer to specifications for proper connecting rod
bearing clearance.
Crankshaft
Crankshaft journals which are more than .001" out
of round or scored must be reground.
Fig. 7 Measuring Piston Diameter
When regrinding, the fillets at the ends of the journals
must be maintained. Connecting rod bearing inserts are
Piston Rings
available in .010", .020" and .030" undersize for reground
Check fit of piston rings in the ring grooves. Also
crankshafts.
check ring gap with rings installed in cylinder bores, Fig.
Screw threads, key ways, tapered ends and all
8. Refer to specifications for correct ring gap and groove
ground and machined surfaces of the crankshaft must
clearance.
not be mutilated or worn excessively.
Main bearing journals must not be worn sufficiently
to prevent the ball bearings being a press fit. The oil seal
ring groove in crankshafts fitted with oil seal rings must
not be worn sufficiently to prevent a good fit on the oil
seal ring. Walls of the oil seal ring grooves must be
square and have a good finish.
Main Bearings
Check for wear or flat spots; if damaged, the
bearings must be replaced. If sleeve bearing type, the
bearing should be checked for scores or wear and
replaced if necessary.
REPAIRS
Discharge Valves and Seats
If discharge valve seats merely show signs of
slight scratches, they can be reclaimed by using a
lapping stone and grinding compound. If seats cannot
be reclaimed, install new seats. After installing new
Fig. 8 Measuring Ring Gap
discharge valves, discharge valve springs and discharge
valve cap nuts, the discharge valve travel should be
Wrist Pins
checked. This can be accomplished from the bottom
Check fit of wrist pins in pistons and connecting
side of cylinder head by measuring the movement of
rods. Wrist pins must be a light press fit in piston. If
discharge valve from its seat. Refer to specifications for
wrist pin is a loose fit in the piston, the wrist pin, piston or
correct
valve
travel.
both must be replaced. Check fit of wrist pin in
connecting rod bushing by rocking the piston. Clearance
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