Subject Page; Description; Engine Lubrication; Disassembly Of The Engine - Chevrolet 1991 Light Duty Truck Repair Manual

6A1-2 2.5L L4 ENGINE
SUBJECT
Main Bearing Installation (W ithout Removing the Crankshaft)..................................................................6A1-21
Camshaft Installation............................................................................................................................................6A1-22
Front Cover In s ta lla tio n .......................................................................................................................................6A1-22
Crankshaft Pulley Hub Insta lla tio n ................................................................................................................... 6A1-23
Piston and Connecting Rod Installation..........................................................................................................6A1-23
Oil Pump Installation............................................................................................................................................6A1-24
Oil Pan In s ta lla tio n ...............................................................................................................................................6A1-25
Oil Pump Driveshaft Installation........................................................................................................................6A1-25
Cylinder Head In s ta lla tio n .................................................................................................................................. 6A1-25
Valve Train Component Installation.................................................................................................................. 6A1-26
Coolant Pump In s ta lla tio n .................................................................................................................................. 6A1-27
Thermostat Housing In s ta lla tio n .......................................................................................................................6A1-28
Intake Manifold Installation................................................................................................................................. 6A1-28
Exhaust Manifold Insta lla tio n ............................................................................................................................. 6A1-29
Flywheel Installation.............................................................................................................................................6A1-29
Engine Accessory Installation............................................................................................................................6A1-29
Engine Set-Up and Testing................................................................................................................................. 6A1-29
S p e cifica tio n s.............................................................................................................................................................6A1-30
Special Tools..............................................................................................................................................................6A1-33

DESCRIPTION

The GM 2.5 Liter engine is an inline four cylinder,
overhead valve, with cast iron block and head.
The crankshaft is supported by five main bearings,
with crankshaft thrust taken at the number five (rear)
bearing.
The camshaft is supported by three bearings and is
gear driven.
The valve train consists of roller type hydraulic lifters,
pushrods, and ball pivot type rocker arms. The valve
guides are integral in the cylinder head.
The connecting rods have precision insert type
crankpin bearings. The piston pins are a press fit in the
connecting rods.
The pistons are cast aluminum alloy. The piston pins
are a floating fit in the pistons.
For engine identification information, refer to GENER­
AL INFORMATION (SEC. OA).

ENGINE LUBRICATION

The oil pump is gear driven from the camshaft (figure
1). Oil is drawn from the oil pan through a pickup
screen and tube. The gear type oil pump has a pres­
sure regulator valve which controls lubrication system
pressure by bypassing excess oil back to the oil pan
sump.
Pressurized oil from the oil pump flows to the full
flow filter. A bypass valve allows oil to bypass the filter
if it becomes clogged or restricted. Oil then flows into
an oil passage which runs along the right side of the
block and intersects the lifter bosses. Oil from this pas­
sage is then routed to the crankshaft main bearings
and camshaft bearings through smaller drilled pas­
sages. Oil is supplied to the connecting rod bearings
by holes drilled in the crankshaft. Oil is supplied to the
rocker arms through holes in the hydraulic lifters which
CONTENTS (cont'd)
feed oil up the pushrods to the rocker arms. The oil is
metered by discs under the pushrod seat.
Many internal engine parts have no direct oil feed
and are supplied by either gravity or splash from other
direct feed components. Timing gears are lubricated by
oil which is supplied through a passage from the front
of the camshaft to a calibrated nozzle above the crank­
shaft gear.
DISASSEMBLY OF THE

TOOLS AND SHOP EQUIPMENT

A clean, well lit work area should be available. Other
necessary aids include: a suitable parts cleaning tank,
compressed air supply, trays to keep parts and fasten­
ers organized, and an adequate set of hand tools.
An approved engine repair stand will aid the work
and help prevent personal injury or damage to engine
compartments.
Special tool are illustrated throughout this section,
and are listed at its end. These tools (or their equiva­
lents) are specially designed to quickly and safely
accomplish the operations for which they are intended.
The use of these tools will also minimize possible dam­
age to engine components.
Some precision measuring tools are required for
inspection of certain critical components. Torque
wrenches will be necessary for correct assembly of var­
ious parts.
This manual assumes that the engine accessories
have been removed. These accessories may include
one or more of the following: hydraulic pump, cooling
fan, generator, TBI unit, distributor.
ENGINE

ACCESSORY REMOVAL

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