Repairs; Piston Rings; Crankshaft; Connecting Rod Bearings - BENDIX TU-FLO 750 COMPRESSOR Manual

should be rebored or honed oversize. Oversized pistons and
piston rings are available in .010 in., .020 in. and .030 in.
oversizes. Cylinder bores must be smooth, straight and
round. Clearance between the cast iron pistons and cylin-
der bores should be between .002 in. minimum and .004 in.
maximum.

PISTON RINGS

Check the pistons for scores, cracks or enlarged ring grooves;
replace the pistons if any of these conditions are found.
Measure each piston with a micrometer in relation to the
cylinder bore diameter to be sure the diametrical clearance
is between .002 in. minimum and .004 in. maximum.
Check the fit of the wrist pins to the pistons and connecting
rod bushings. The wrist pin should be a light press fit in the
piston. If the wrist pin is a loose fit, the piston and pin as-
sembly should be replaced. Check the fit of the wrist pin in
the connecting rod bushing by rocking the piston. This clear-
ance should not exceed .0007 in. Replace the connecting
rod and cap assembly which includes the wrist pin bush-
ings if excessive clearance is found. Check the fit of the
rings in the piston ring grooves. Check the ring gap with the
rings installed in the cylinder bores. Refer to Figure 12 for
correct gap and groove clearances.

CRANKSHAFT

Check the crankshaft threads, keyways, tapered ends and
all machined and ground surfaces for wear, scores, or dam-
age. Standard crankshaft journals are 1.1242 in. - 1.1250 in.
in diameter. If the crankshaft journals are excessively scored
SIDE CLEARANCE
.002
.004
STANDARD
PISTON
RING
END GAP
FIGURE 12 - RING CONFIGURATION
EXPANDER
RING
OIL RING
End
Ring
Gap
.002
Compression
.013
.010
Segment
.040
or worn or out of round and cannot be reground, the com-
pressor must be replaced. Connecting rod bearing inserts
are available in .010 in., .020 in. and .030 in. undersizes for
compressors with reground crankshafts. Main bearing jour-
nals must be maintained so the ball bearings are a snug fit
or so that no more than .005 in. clearance exists between
the precision sleeve main bearing and the main bearing jour-
nals on the crankshaft. Check to be sure the oil passages
are open through the crankshaft.

CONNECTING ROD BEARINGS

Used bearing inserts must be replaced. The connecting rod
and cap are a matched set and therefore the caps must not
be switched or rotated end for end. Make sure the locating
tangs on the inserts engage with the locating notches in the
rod and cap. Clearance between the connecting rod journal
and the connecting rod bearing must not be less than .0003
in. or more than .0021 in. after rebuilding.

REPAIRS

UNLOADER
A new cylinder head maintenance kit should be used when
rebuilding. Note: The entire contents of this kit must be
used. Failure to do so may result in compressor fail-
ure. The unloader pistons in the kit are prelubricated with a
special lubricant piece number 239379 and need no addi-
tional lubrication. Install the springs and unloader pistons in
their bores being careful not to cut the o-rings. Install the
unloader cover gasket and unloader cover and secure the
cover cap screws. Tighten the cap screws to 175-225 in.
Ibs. in a crossing pattern after first snugging all screws.
DISCHARGE VALVES, VALVE STOPS AND
SEATS
If the discharge valve seats merely show signs of slight wear,
they can be dressed by using a lapping stone, grinding
.000
compound and grinding tool however it is recommended that
.006
a cylinder head maintenance kit be used. Install new
discharge valve springs and valves. Screw in the discharge
valve seats, and tighten to 70-90 ft.-lbs. Discharge valve travel
should be between .030 in. to .046 in. To test for leakage by
the discharge valves, apply 100 psi to the cylinder head
discharge port and apply a soap solution to the discharge
valve and seats. Leakage in the form of soap bubbles is
permissible. If excessive leakage is found, leave the air
pressure applied and with the use of a fiber or hardwood
dowel and a hammer, tap the discharge valves off their seats
several times. This will help the valves to seat and should
reduce the leakage. With the air pressure still applied at the
discharge port of the cylinder head, check for leakage around
the discharge valve stop on the top of the cylinder head
casting. No leakage is permitted.
11