Pontiac FIREBIRD 1972 Service Manual page 524

6-12 1972 PONTIAC SERVICE MANUAL
Fig. 6-7 Cylinder Block and Bearing Caps
constant diameter across the thrust faces. Two compres-
sion rings and one oil control ring are used, all of which
are located above the piston pin.
The piston top configuration is shown in Fig. 6-9.
Piston pins are offset 1/16" toward thrust side (right-hand
side) to provide a gradual change in thrust pressure
against the cylinder wall as the piston travels its path. This
feature provides quieter engine operation. Pins are
chromium steel and have a floating fit in the pistons. They
are retained in the connecting rods by a press fit.
Connecting rods are made of forged steel. Full pressure
lubrication is directed to the connecting rods by drilled oil
passages from the adjacent main bearing journal. Oil holes
at the connecting rod journals are located so that oil is
supplied to give maximum lubrication just prior to full
bearing load.
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through a bakelite fabric composition gear with steel hub
(Fig. 6-8).
VALVE TRAIN
Cam lobes are ground, hardened and tapered with the
high side toward the rear. This, coupled with a spherical
face on the lifter. causes valve lifters to rotate.
Camshaft bearings are lubricated through oil holes which
intersect the main gallery. The main gallery runs parallel
to the cylinder bores along the right side of the block.
PISTONS AND CONNECTING RODS
The pistons are aluminum alloy, tin plated, with steel
struts to control expansion and give added strength (Fig.
6-9). Pistons are cam ground so that the diameter across
the thrust faces is larger than the diameter fore and aft of
the engine. The steel struts force expansion and contrac-
tion to occur to the front and rear and thus provides a
A very simple ball pivot-type train is used (Fig. 6-10).
Motion is transmitted from the camshaft through the hy-
draulic lifter and push rod to the rocker arm. The rocker
arm pivots on its ball and transmits the camshaft motion
to the valve. The rocker-arm ball is retained by a nut.
The maximum in durability is assured by the use of
stamped steel rocker arms. In addition, all friction points
in the valve train are positively lubricated.
The cylinder head has straight valve guides cast integrally
(Fig. 6-10). External shields are used on both intake and
exhaust valves to reduce the amount of oil splashed
against the stems. Valve stem seals are used on intake and
exhaust valves to prevent oil from entering the valve
guides.
A single valve spring is used.
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r O I L SPURT HOLE UP
Fig. 6-8 Timing Gears Fig. 6-9 Piston and Rod Assembly