Pontiac Fiero 1988 Service Manual page 302

2.5L ENGINE 6A1-1
SECTION 6A1
2.5 LITER L4 ENGINE
CONTENTS
G e n e r a l D e s c r i p t i o n
,. 6A1-1
Cylinder Block 6A1-1
Cylinder Head ,. 6A1-1
Valve Train 6A1-1
Valve Lifters 6A1-1
Intake Manifold 6A1-1
Exhaust Manifold 6A1-2
Camshaft and Drive , 6A1-2
Pistons and Connecting Rods 6A1-2
Crankshaft and Bearings 6A1-3
Force Balancer 6A1-3
Oil Pump 6A1-3
Engine Lubrication 6A1-3
S e r v i c e P r o c e d u r e s
6A1-3
Rocker Arm Cover 6A1-3
Rocker Arms, Pushrods and Guides 6A1-3
Valve Spring, Shield and/or Seals 6A1-5
Intake Manifold 6A1-6
Valve Lifters 6A1-6
Cylinder Head 6A1-7
Force Balancer Assembly 6A1-8
Oil Pump/Pressure Regulator Valve 6A1-9
Rear Main Bearing Oil Seal and/or
Flywheel
6A1-10
Connecting Rod and Piston 6A1-11
Crankshaft 6A1-11
O n C a r S e r v i c e
6A1-12
Engine and Transaxle Mounts 6A1-12
Push Rod Cover 6A1-15
Oil Pan
6A1-15
Timing Gear Cover/Front Seal 6A1-16
Engine Assembly 6A1-17
Exhaust Manifold 6A1-18
Camshaft 6A1-18
Engine Specifications 6A1-21
Special Tools 6A1-24
GENERAL DESCRIPTION
CYLINDER BLOCK
The cylinder block is made of cast iron and has
four (4) in-line cylinders which are numbered from
front to rear 1 through 4. Five main bearings support
the crankshaft, which is retained by recessed bearing
caps that are machined with the block for proper
alignment and clearance. Because roller tappets are
used, lifter retainers and guides are installed in the
block to keep the lifters in proper position.
Cylinders are completely encircled by coolant
jackets. (For details of engine cooling system, see
ENGINE COOLING, Section 6B).
CYLINDER HEAD
The cast iron cylinder head provides a
compression ratio of 8.3:1. It is cast with individual
intake and exhaust ports for each cylinder. Valve
guides are integral and rocker arms are retained on
individually threaded shoulder bolts.
Combustion chambers are cast to insure uniform
shape for all cylinders and enhance swirl in the
cylinder. Spark plugs are located near intake valves for
maximum power.
Intake valves are large to provide easy breathing
for high combustion efficiency. Intake and exhaust
valve seat angles are 46° to assure valve-to-seat contact
at the outer diameter of the seat. Face angles of both
intake and exhaust valves are 45°. The cylinder head
has straight valve guides, cast integrally. Positive valve
stem seals are used on intake and exhaust valves to
prevent excess oil from entering the valve guides.
Valve springs with external spring dampers
control spring surge at high RPM.
V A L V E T R A I N
A very simple ball pivot-type valve train is used
(Fig. 1). Motion is transmitted from the camshaft
through the roller hydraulic 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 and ball are retained by a shoulder bolt.
VALVE LIFTERS
Hydraulic valve lifters have roller tappets to
reduce friction between the valve lifter and camshaft
lobe. Lifter retainers and guides are installed in the
block to keep lifters from rotating on the camshaft
lobes.
Hydraulic valve lifters keep all parts of the valve
train in constant contact and adjust automatically to
maintain zero lash under all conditions.
The hydraulic lifter rides in a cylinder block boss
and consists of a steel body with a roller tappet, a
plunger spring, ball check retainer, ball check spring,
ball check, plunger, oil metering valve, push rod seat
and retainer ring.
INTAKE MANIFOLD
The intake manifold is cast aluminum and uses a
single level design. A cast passage in the manifold
allows engine coolant to pass through to utilize hot
water heat for intake air and EFI system warm-up. An
EGR port is also cast in the manifold and receives
exhaust gases from an internal exhaust passage in the
cylinder head.