Bendix Commercial Vehicle Systems TU-FLO 750 COMPRESSOR 6/08 - Manual (Page 11)

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in. 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
cylinder 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 fi t of the wrist pins to the pistons and connect-
ing rod bushings. The wrist pin should be a light press fi t
in the piston. If the wrist pin is a loose fi t, the piston and
pin assembly should be replaced. Check the fi t of the wrist
pin in the connecting rod bushing by rocking the piston.
This clearance should not exceed .0007 in. Replace the
connecting rod and cap assembly which includes the wrist
pin bushings if excessive clearance is found. Check the fi t
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 or worn or out of round and cannot be reground, the
compressor must be replaced. Connecting rod bear-
ing inserts are available in .010 in., .020 in. and .030 in.
undersizes for compressors with reground crankshafts.
Main bearing journals must be maintained so the ball bear-
ings are a snug fi t or so that no more than .005 in. clearance
exists between the precision sleeve main bearing and the
main bearing journals 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
failure. The unloader pistons in the kit are prelubricated
with a special lubricant piece number 239379 and need
no additional 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 fi rst 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
compound and grinding tool however it is recommended
that 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 fi ber 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.
SIDE CLEARANCE
.000
.006
STANDARD PISTON
RING
.002
.004
OIL RING
EXPANDER
RING
END GAP
.002
.013
.010
.040
Segment
Ring
End
Gap
FIGURE 12 - RING CONFIGURATION
Compression