Pontiac FIREBIRD 1972 Service Manual page 604

6-92 1972 PONTIAC SERVICE MANUAL
PISTON RINGS
REMOVE
Remove piston and rod assembly. See CONNECT-
ING ROD AND PISTON ASSEMBLY
-
REMOVE
AND REPLACE.
Remove piston rings using proper tool.
Clean carbon, varnish, and gum from piston surfaces,
including under side of piston head. Clean ring
grooves, and oil holes in oil ring groove, using suita-
ble cleaning tools and solvent.
Carefully examine piston for rough or scored bearing
surfaces; cracks in skirt or head; cracked, broken, or
worn ring lands; scored, galled, or worn piston
bosses. Damaged or faulty pistons should be re-
placed.
Inspect bearing shells to see that they are serviceable.
Fit of bearings should be checked when engine is
being assembled.
Inspect cylinder bores for out-of-round or excessive
taper. See CYLINDER BORES-INSPECT.
PISTON RING CHECK AND INSTALL ON PISTON
Two compression rings and one 3-piece oil control ring,
all above the piston pin, are used on pistons for all engines.
The compression rings are taper faced and also have either
a step or chamfer on the inside diameter of the bottom
side. The top compression ring is molybdenum filled,
which results in the center section of ring sealing edge
appearing porous or grainy. The lower compression ring
varies depending upon the engine. See specifications at the
end of this section.
Regardless of engine type, always install compression
rings with the stamped markings toward the top of piston.
New rings are serviced for the standard size pistons, and
for .01OV and .030" oversize pistons. When selecting rings,
be sure they match the size of the piston on which they
are to be installed, i.e., standard rings for standard pistons,
,010" oversize rings for .010" oversize pistons, etc. Ring
gap and side clearance should be checked while installing
as follows:
1. Check pistons to see that ring grooves and oil return
holes have been properly cleaned.
2. Place ring down at the bottom of the ring traveled
part of the cylinder bore in which it will be used.
Square ring in bore by pushing it into position with
head of piston.
Fig. 6-163 Checking Ring Gap
3. Measure gap between ends of ring with feeler gauge
(Fig. 6-163). Gaps should be as follows:
Compression Ring
All except 307
........................................
,010"
-
.030"
......................................
307
-
Top Ring .010"
-
.020"
Second Ring
....................................
.OIOM
-
.020"
OilRing(Al1)
..............................................
015"-.055"
Incorrect ring gap indicates that wrong size rings are be-
ing used. If rings are selected according to the size of the
bore (standard, .010" oversize, etc.), they should have the
proper gap. It should not be necessary to alter ring gap by
filing.
4. Install rings on piston, using J 8021 or J 71 17 to
prevent breakage or fracture of rings, or damage to
pistons.
5. Measure side clearance of rings in ring groove as each
ring is installed (Fig. 6-164). Clearance with new
pistons and rings should be .0015"-.005" (all except
307 engine) or for 307 engine as follows: Top Ring
-
.0012"
-
.0027", Second Ring
-
.0012"
-
.0032", Oil
Ring
-
.002"
-
.007".
If side clearance is excessive, piston should be replaced.
CRANKSHAFT
CHECK
These checks are to be made with oil pan and baffle
removed and with all main caps and rods installed and
properly torqued.