GMC 1989 Light Duty Truck, Repair Manual, Page: 358 / 998

6A1-2 2.5 LITER L4 ENGINE
CONTENTS (CONT.)
SUBJECT PAGE
Assembly of Engine Cont.
Oil Pan Installation................................................................................................................................................................. 6 A 1 -2 7
Oil Pump Driveshaft Installation........................................................................................................................................ 6 A 1 -2 7
Cylinder Head Installation....................................................................................................................................................6 A 1 -2 7
Valve Train Component Installation................................................................................................................................. 6 A 1 -2 9
W ater Pump In s ta lla tio n ...................................................................................................................................................... 6 A 1 -2 9
Therm ostat Housing In s ta lla tio n ...................................................................................................................................... 6 A 1 -3 0
Intake Manifold Installation................................................................................................................................................. 6 A 1 -3 0
Exhaust Manifold In s ta lla tio n .............................................................................................................................................6 A 1 -3 0
Flywheel In s ta lla tio n .............................................................................................................................................................6 A 1 -3 0
Engine Accessory In s ta lla tio n ...........................................................................................................................................6 A 1 -3 0
Engine Set-Up and T e s tin g ................................................................................................................................................. 6 A 1 -3 0
S p e c ific a tio n s .............................................................................................................................................................................6 A 1 -3 3
Special T o o ls ............................................................................................................................................................................... 6 A 1 -3 6
DESCRIPTION
The GM 2.5 L 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 c o n n e c tin g rods have p re c is io n in s e rt typ e
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 pistions.
For engine identification information, refer to GENERAL
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. A bypass valve in the pickup screen insures
adequate oil flow if the screen becomes restricted. The
gear type oil pump has a pressure 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 passage is then
routed to the crankshaft main bearings and cam shaft
bearings through smaller drilled passages. 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 w hich 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 crankshaft gear.