Pontiac Fiero 1988 Service Manual page 303

6A1-2 2.5L ENGINE
Fig. 1 Valve Train
H20003-6A4
Fig. 2 Intake Manifold
E X H A U S T M A N I F O L D
The exhaust manifold is made of stainless steel
and directs exhaust gases from the combustion
chambers.
C A M S H A F T A N D D R I V E
The modular iron camshaft is supported by three
bearings and is gear driven. A powdered metal
crankshaft gear drives the camshaft through a
pheonolic fabric composition gear with a steel hub
(Fig.
4 ) .
Cam lobes are hardened and ground with no front
to rear taper; since lifters do not "orbit" with cam
rotation.
Camshaft bearings are lubricated through oil
holes which intersect the main gallery.
H20004-6A4
Fig. 3 Exhaust Manifold
Fig. 4 Camshaft and Crankshaft Gears
P I S T O N S AND CONNECTING RODS
The pistons are of a lightweight, cast aluminum
slipper skirt type and cam ground so that the diameter
across the thrust face is larger than the diameter fore
and aft of the engine. Two compression rings and one
oil control ring are used, all of which are located above
the piston pin (Fig. 5).
Fig. 5 Piston and Rod Assembly
Piston pins are offset toward thrust side
(right-hand side) to provide a gradual change in thrust
pressure against the cylinder wall as the piston travels
its path. Pins are tempered 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 Armasteel. Full
pressure lubrication is directed to the connecting rods
by drilled oil passages from the adjacent main bearing