Pontiac tempest 1968 Service Manual page 256

V-8 E N G I N E 6-39
sizes are used (Figs. 6-69 and 6-70). Both types
have fully machined combustion chambers. Valve
guides are cast integral with the cylinder head and
valve heads are surrounded by water jackets.
A l l cylinder heads are new for 1968. The cylinder
heads have been redesigned to reflect the use of
revised valve angles and-increased distance between
centrelines of valves. Combustion chambers have
also been redesigned for improved efficiency.
CAMSHAFT AND DRIVE
Five different camshafts are used. The engine
charts (Figs. 6-1 and 6-2) show the application of
each. Camshafts can be identified by a letter stamped
on the front end of the shaft.
PISTONS AND CONNECTING RODS
The pistons used In a l l compression ratio engines
are flat on top as shown i n F i g . 6 - 7 1 . The top of the
piston has a relief machined into It for valve
clearance.
VALVE MAIN
A l l V-8 engines utilize the simple ball pivot-type
valve t r a i n , consisting of the valve, rocker a r m ,
push rod, and valve l i f t e r .
Rocker studs are pressed Into the cylinder head
on the standard engines and are screwed i n on
G.T.O., Grand P r i x , and 428. A l l heads use stamped
steel push rod guide plates to minimize push rod
guide wear (Fig. 6-72).
Umbrella type valve guide seals are used on
HEPHHHEii
F i g . 6 - 6 9 Combustion Chamber—Standard Head
350H.O., 400H.O., 428 and G.T.O. 4 bbl. Intake
valves i n addition to the "O" ring seals (Fig. 6-72).
Double valve springs are used on a l l engines.
PERIODIC SE1WJCE
There are no periodic services required on the
mechanical portions of the engine. ' Periodic services
connected with the engine consist of tune-up, lubrica­
tion, replacing o i l f i l t e r , etc. Procedures and rec­
ommendations for these services w i l l be found i n
appropriate sections of this manual, and the owners
manual.
F i g . 6 - 7 0 Combustion Chamber—Large Head
F i g . 6-68 Cylinder Block—428 and 400 Ram A i r Engines