BENDIX TU-FLO 750 COMPRESSOR Dati di servizio - Pagina 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

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

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

.000

that a cylinder head maintenance kit be used. Install new

.006

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.