Pontiac FIREBIRD 1972 Service Manual page 553

SIX CYLINDER ENGINE 6-4 1
PISTON RINGS
REPLACE
1. Remove connecting rod and piston assembly (See
"CONNECTING ROD AND PISTON ASSEM-
BLY
-
REMOVE AND REPI.,ACE" in this section).
2. Clean carbon, varnish, and gum from piston surfaces,
including underside of piston head. Clean ring
grooves, and oil'holes in oil ring groove, using suita-
ble cleaning tools and solvent.
3. 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.
4. Inspect bearing shells to see that they are not da-
maged. Fit of bearings should be checked when en-
gine is being assembled.
5. Inspect cylinder bores for out-of-round or excessive
taper. If bores show excessive out-of- round or taper,
or if cylinder walls are badly scored, scratched or
worn beyond specified limits, the cylinder block
should be rebored and new pistons and rings in-
stalled.
PISTON RINGS
INSTALL
Two compression rings and one 3-piece oil control ring,
all above the piston pin, are used on pistons. The top
compression rings are taper faced and also have either a
step or a chamfer on the inside diameter of the top side.
The top compression ring is chrome plated. The lower
compression ring may have a step.
Always install compression rings with the side marked
with letters "GM" toward the top of the piston.
New rings are serviced for the standard size pistons, and
for .005", .010", .020" 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 stand-
ard pistons, .01OV oversize rings for .010" oversize pistons,
etc. Ring gap and side clearance should be checked while
installing rings 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
Fig. 6-67 Checking Ring Gap
3. Measure gap between ends of ring with feeler gage
(Fig. 6-67). Gaps should be as follows:
Upper Compression Ring
........................
.0 10"
-
.020M
Lower Compression Ring
........................
.0 10"
-
.02OW
Oil Ring
...............................................
.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, .005" 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 suitable ring installing
tool such as 5-7135, to prevent breakage or fracture
of rings, or damage to pistons.
5. Measure side clearance of rings in ring groove (Fig.
6-68) as eacha ring is installed. Clearance with new
pistons and rings should be as follows:
Upper Compression Ring
..................
.00 12"
-
.0027"
Lower Compression Ring
....................
.0012"
-
.0032"
Oil Control Ring
......................................
.001"
-
.005"
If side clearance is excessive, piston should be replaced.
,
CONNECTING ROD AND PISTON
ASSEMBLY
REPLACE
part of the cylinder bore in which it will be used.
Square ring in bore by pushing it into position with
head of piston.
-
.
-
1. Install connecting rod bolt guide set 5-5239 on con-
necting rod bolts (Fig. 6-69).