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Sec. 4
Page 68
GM COACH MAINTENANCE MANUAL
AIR COMPRESSOR AND GOVERNOR
CYLINDER
BLOC
PISTON
RING
CYLINDER
BLOCK
MEASURING PISTON RING GAP
TP 18H
Figure 21-Compressor Cylinder Bore and Piston Ring Inspection
12.
Piston Rings.
Check fit of piston rings in ring grooves in
pistons (fig. 22). Clearance between the ring and
the ring groove must not be less than .0015 inch
or more than .0025 inch. Install ring in cylinder
bore and measure ring gap (fig. 21).
Used rings
which have a gap of more than .020 inch must be
replaced. New rings must have .010 to .015 inch
gap.
13.
Connecting Rods and Bearings.
Check fit of connecting rod bearings on crank-
shaft journals.
Clearance between bearing and
crankshaft journal must not exceed .002 inch.
Clearance between side of connecting rod and
cheek on crankshaft must not exceed .015 inch.
Replace rod bearing inserts
if
worn, cracked, or
flaked.
14. Crankshaft.
Crankshaft journals which are out-of-round
more than .001 inch or bruised must be reground.
TYPE RING
Compression~
Scraper
Scraper Segment
Compression~
O i l - - - - - - ~ - - _ _ ,
Oil Segment
-3 ~----'
Oil Expander
PISTON RING ARRANGEMENT
.0015"
.0025"
+r
RING TO GROOVE
CLEARANCE
.010"
.015"
-11--
c:=J[=:!
RING GAP WITH
RING IN CYLINDER
TP 5525
Figure 22-Piston Ring Arrangement and Clearances
When regrinding, the fillets at the ends of the
journals must be maintained. Connecting rod bear-
ings are available .010, .020, and .030 inch under-
size for reground crankshafts.
All ground and
machined surfaces must not be mutilated or ex-
cessively worn.
Main
bearing journal must not
be worn sufficiently to prevent ball bearings be-
ing a light press fit.
15. Ball Bearings.
Examine bearings for wear or flat spots and
replace if damaged.
16. Springs.
Check tension of all springs in accordance
with "Specifications" at end of this section and
replace any which are weak or broken.
COMPRESSOR REPAIR
UNLOADING VALVE BUSHINGS
If unloading valve bushings require replace-
ment as previously indicated in step 4 under
''In-
spection," remove bushings by pressing them out
through the top of the cylinder head.
Press new
CII
0
0
+I
,.,
0)
CII
t\i
'
Figure 23-Unloading Valve Bushing Installation
1
j
l
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