Pontiac tempest 1968 - Page 256

V-8 ENGINE
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.
All 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 all compression ratio engines
are flat on top as shown in Fig. 6-71. The top of the
piston has a relief machined into It for valve
clearance.
VALVE MAIN
All V-8 engines utilize the simple ball pivot-type
valve train, consisting of the valve, rocker arm,
push rod, and valve lifter.
Rocker studs are pressed Into the cylinder head
on the standard engines and are screwed in on
G.T.O., Grand Prix, and 428. All 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
Fig. 6-69 Combustion Chamber—Standard Head
350H.O., 400H.O., 428 and G.T.O. 4 bbl. Intake
valves in addition to the "O" ring seals (Fig. 6-72).
Double valve springs are used on all 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 oil filter, etc. Procedures and rec-
ommendations for these services will be found in
appropriate sections of this manual, and the owners
manual.
Fig. 6-70 Combustion Chamber—Large Head
Fig. 6-68 Cylinder Block—428 and 400 Ram Air Engines