2.5l 4-cyl - VIN [e] GMC S15 Pickup

ENGINE IDENTIFICATION

Note. For engine repair procedures not covered in this article, see ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article in the GENERAL INFORMATION section.

Engine may be identified by eighth character of Vehicle Identification Number (VIN). VIN is stamped on metal tag attached to left side of dash, near windshield. Engine identification number is stamped on machined pad on left rear of engine block, below cylinder head.

ENGINE IDENTIFICATION CODES

ENGINE

See ENGINE REMOVAL article.

ENGINE OVERHAUL

Note. See ENGINE OVERHAUL PROCEDURES article for detailed information on performing basic engine overhaul and checking procedures.

INTAKE MANIFOLD

1. Place transmission gear selector in park (neutral on manual transmissions). Set parking brake and block drive wheels. Loosen fuel filler cap to relieve tank pressure. Disconnect 3-terminal electrical connector at fuel tank. Start engine and allow to run until engine stalls due to lack of fuel. Crank engine for 3 seconds to remove any fuel pressure left in fuel lines. Fuel lines are now safe for servicing. WARNING: To avoid possible personal injury and fire danger, fuel pressure must be relieved as outlined in step 1).
2. Disconnect cruise control transducer (if equipped). Disconnect water pump by-pass hose at intake manifold. Remove rear alternator adjusting bracket. Disconnect alternator brace and move aside. Disconnect cruise control cable. Disconnect and label all vacuum hoses.
3. Disconnect vacuum line hold-down at thermostat housing and intake manifold. Disconnect heater hose at intake manifold. Disconnect coil. Remove generator rear bracket. Remove emissions sensor bracket at the manifold. Remove intake manifold bolts and washers. Remove manifold.

Installation

To install, reverse removal procedure. Apply sealant to bolts No. 4, 5 and 6. (Scheme 1) Tighten bolts to specifications. See TORQUE SPECIFICATIONS table.

Removal

Disconnect negative battery cable. Remove rear A/C bracket. Disconnect exhaust pipe at manifold. Remove air cleaner and heat stove tube. Disconnect oxygen sensor wire. Do not remove oxygen sensor from manifold unless exhaust manifold requires replacement. Remove exhaust manifold bolts. Remove exhaust manifold.

To install, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS. (Scheme 2)

Scheme 1

Scheme 2

CYLINDER HEAD

1. Disconnect negative battery cable. Drain cooling system. Disconnect spark plug wires at spark plugs. Remove A/C bracket and compressor and set aside. Disconnect vacuum line and wiring harness at thermostat housing. Disconnect and label all vacuum lines. Remove oil dipstick tube and unbolt and remove oil filler tube. Remove valve cover bolts. Remove valve cover using Remover (J-34144-A).
2. Remove vacuum lines, fuel lines and wiring at intake manifold and throttle body. Disconnect accelerator, cruise control and throttle valve cables. Disconnect water pump by-pass and heater hoses at intake manifold. Remove alternator brackets and set alternator aside. Remove thermostat housing. Disconnect ground cable and wiring harness bracket at rear of cylinder head.
3. Disconnect exhaust pipe at manifold. Disconnect fuel filter and fuel line brackets at rear of cylinder head. Disconnect wiring harness connector at fuel filter. Disconnect coil and spark plug wires. Disconnect oxygen sensor wire.
4. Loosen rocker arms and rotate to one side. Remove push rods. Remove head bolts. Remove cylinder head with intake and exhaust manifolds attached. Remove intake and exhaust manifolds.

Note. See ENGINE OVERHAUL PROCEDURES article in this section to prepare head for installation.

Note. This procedure has been revised due to TSB Chevrolet 88-52, dated 09/23/1987.

1. To install, reverse removal procedure. Apply sealant to bolt No. 9. Tighten all head bolts to 18 ft. lbs. (24 N.m) in specified sequence. (Scheme 3)
2. Tighten all head bolts in sequence (EXCEPT bolt No. 9) to 27 ft. lbs. (35 N.m). Retighten bolt No. 9 to 18 ft. lbs. (24 N.m).
3. Draw a line across head of each bolt with a marking crayon to mark position of bolt.
4. Tighten all bolts an additional 90 degrees (1/4 turn) in specified sequence.

Scheme 3

VALVES

Note. New valves must not be lapped. Lapping will destroy protective coating on valve face.

VALVE ARRANGEMENT

I-E-I-E-E-I-E-I (Front-to-rear).

Removal & Installation

1. With cylinder head removed and disassembled, check valve stem-to-guide clearance. See ENGINE OVERHAUL PROCEDURES article. Check clearance with valve head positioned .063" (1.6 mm) away from valve seat.
2. Use Valve Guide Cleaner (J-8101) for cleaning guides. Use Valve Guide Reamers (J-5830-01 or J-6621) to ream guides for installation of valves with oversize stems. Intake service valves are available in 003" (.08 mm) and .005" (.13 mm) oversizes. Exhaust service valves are available in .003" (.08 mm) oversize.

Note. For additional valve specifications, see VALVES & VALVE SPRINGS in ENGINE SPECIFICATION tables article. For additional service information, see ENGINE OVERHAUL PROCEDURES article.

1. Disconnect negative battery cable. Drain cooling system. Disconnect spark plug and coil wires, and bracket at intake manifold.
2. Disconnect fuel lines at side cover. Remove oil pressure sending unit. Remove fuel pipes and clips at side cover. Remove wiring harness brackets from side cover. Remove 4 nuts from side cover studs.
3. Reverse and reinstall 2 nuts onto 2 inner studs. Install 2 remaining nuts onto same inner studs.
4. Using 2 wrenches, hold inner nut stationary. Jam 2 nuts tightly together. Using a wrench on inner nut, alternately unscrew studs until cover breaks loose. Remove jammed nuts from studs. Remove cover from studs.

Clean gasket sealing surfaces. Inspect studs and rubber washers for damage. Replace as necessary. Tighten studs to 90 INCH lbs. (10 N.m). Apply a 3/16" thick, continuous bead of RTV to side cover. Install side cover and tighten nuts to 90 INCH lbs. (10 N.m). To complete installation, reverse removal procedure.

Scheme 4

HYDRAULIC ROLLER VALVE LIFTERS

Note. For cleaning and inspection of hydraulic lifters, see ENGINE OVERHAUL PROCEDURES article.

1. Remove valve cover using Remover (J-34144-A). Remove push rod cover as previously described. Loosen rocker arm and rotate for clearance from push rod. Remove push rod, studs, lifter retainer and guide. (Scheme 4) Using lifter remover or magnet, remove lifters.
2. Check lifter-to-bore clearance. Standard clearance is.0025" (.064 mm). Standard diameter of lifter is.8420-.8427" (21.387-21.405 mm). Standard lifter bore diameter is.8435-.8445" (21.425-21.450 mm).
3. To install, reverse removal procedure. If new lifter is being installed, sealer coating on inside of lifter must be removed. Coat lifter body and roller with engine oil. Ensure push rod seats properly in lifter. Ensure lifter is installed on base circle of camshaft.

1. Disconnect negative battery cable. Disconnect power steering reservoir from fan shroud (if equipped). Remove upper fan shroud. Remove drive belt, fan and pulley. Remove alternator, brackets and brace.
2. Remove crankshaft pulley and hub bolts. Remove crankshaft pulley and hub. Disconnect lower radiator hose at water pump. Remove front cover bolts and front cover.

1. Clean mating surfaces of engine block, oil pan and front cover. Apply a continuous bead of RTV on cover and to oil pan at front cover sealing surface. Install Front Cover Centering Tool/Seal Installer (J-34995) in front cover oil seal. Install front cover to block.
2. Install and partially tighten 2 oil pan-to-front cover bolts. Install front cover-to-block bolts and tighten all bolts to 90 INCH lbs. (10 N.m). Remove centering tool. To complete installation, reverse removal procedure.

Remove engine drive belt. Remove pulley and hub bolts. Remove hub and pulley from crankshaft. Using large screwdriver, pry oil seal from front cover. DO NOT distort front cover sheet metal.

1. Drive seal into place using Installer (J-34995). Coat oil seal contact area of balancer with engine oil.
2. Position hub on crankshaft and slide into position until it bottoms against crankshaft gear. Install center hub bolt and tighten. Install pulley-to-hub bolts using Loctite and tighten to specification. Install drive belt and adjust tension.

Scheme 5

Scheme 6

1. Disconnect negative battery cable. Remove air cleaner. Disconnect power steering reservoir from fan shroud (if equipped). Remove upper fan shroud. Remove drive belt, fan and fan pulley. Remove crankshaft pulley, hub and front cover as previously described.
2. Remove EGR valve and vacuum lines at intake manifold and thermostat housing. Remove valve cover using Remover (J-34144-A). Loosen rocker arm bolts and pivot rocker arms aside. Remove push rods. Remove intake manifold, push rod side cover and lifters as previously described. Remove distributor.
3. Remove radiator. Unbolt A/C condenser and set aside. Raise and block condenser up high enough to clear camshaft. Remove alternator and bracket. Remove grille and filler panel.
4. Remove oil pump drive shaft retainer plate bolts. Remove bearing and shaft assembly. (Scheme 5)
5. Remove 2 camshaft thrust plate retaining bolts by working through holes in camshaft gear. (Scheme 6) Remove camshaft and gear assembly by pulling it through front of block. Use care not to damage camshaft bearings.
6. Place camshaft through opening in press plates on arbor press. Support gear (DO NOT support thrust plate) and press camshaft out of timing gear (if necessary). Position thrust plate so that Woodruff key in camshaft does not damage thrust plate during removal.

Inspection

1. Inspect camshaft lobes and journals for scratches, pitting and wear. Inspect timing gear for damaged teeth. Check camshaft journals for out-of-round condition. If journals exceed specification, replace camshaft.
2. Check camshaft end play (between thrust plate and first camshaft journal). Replace thrust plate if clearance exceeds specification. Replace spacer ring if clearance is less than specification.
3. Check camshaft journal runout. If runout exceeds specification, replace camshaft. Check camshaft lobe lift. If not to specification, replace camshaft.

1. Support camshaft at back of front journal in arbor press using press plate adapters. Install gear spacer ring and thrust plate over end of camshaft. Install Woodruff key in shaft keyway. Install camshaft gear and press it onto camshaft until it bottoms against gear spacer ring. Check end play.
2. Coat camshaft lobes with Oil Supplement (1051396). Coat journals with engine oil. Install camshaft in engine block. Be careful not to damage camshaft bearings. Align timing marks by rotating camshaft and crankshaft until timing marks on gear teeth line up. (Scheme 7)
3. Install 2 camshaft thrust plate-to-block bolts and tighten. Install timing gear cover using centering tool as previously described. Line up hub keyway to crankshaft key, install hub and tighten center bolt to specification.
4. Install lifters, push rods and push rod cover as previously described. Install oil pump shaft and gear assembly. To install distributor, turn crankshaft 360 degrees to firing position of No. 1 cylinder (timing marks aligned on balancer and timing pad and both No. 1 cylinder valves closed).
5. Install distributor in original position and align shaft with rotor arm toward No. 1 plug contact. Pivot each rocker arm over push rod and tighten rocker arm bolt (with lifter on base circle of camshaft). To complete installation, reverse removal procedure.

Scheme 7

With engine, flywheel and camshaft removed, drive out expansion plug from rear camshaft bearing. Remove by driving out from inside. Using Universal Camshaft Bearing Remover/Installer (J-33049), drive front bearing out toward rear of engine and rear bearing toward front. Drive center bearing out toward rear of engine.

Install bearings in block in reverse order of removal. Ensure oil hole in camshaft bearings and cylinder block line up. Install front camshaft bearing with bearing recessed about 1/8" into engine block. This uncovers oil hole to timing gear oil nozzle. Reverse removal procedure to complete installation.

1. When removing piston and rod assembly, ensure connecting rod, rod cap and piston are marked for proper reassembly into matching cylinder. When installing piston and rod assembly, ensure ring gaps are properly spaced. (Scheme 8) Ensure oil hole in bearing insert aligns with oil hole in connecting rod. NOTE: When installing pistons, notch on top of piston faces front of engine.
2. After installation, check rod bearing clearance using Plastigage method. Check rod side clearance after tightening rod nuts to specification. See ENGINE OVERHAUL PROCEDURES article.

Scheme 8

FITTING PISTONS

1. Check cylinder bore taper and out-of-round. See ENGINE OVERHAUL PROCEDURES article. See ENGINE SPECIFICATIONS tables.
2. Measure diameter of cylinder bore parallel to crankshaft at a point 2.50" (60 mm) from top of cylinder bore. Measure outer diameter of piston at centerline of pin bore, 90 degrees to pin bore axis.
3. Subtract piston diameter from cylinder bore diameter to determine if piston-to-bore clearance is acceptable. If not acceptable, determine if a new piston can fit cylinder bore. If not, cylinder bore must be reconditioned.
4. Before cylinder reconditioning, ensure that main bearing caps are in place and tightened to specification to avoid distortion during reconditioning operation.
5. Measure new piston and hone cylinder to correct clearance. After reconditioning operation, allow bore to cool, then clean bore with hot soapy water and oil cylinder walls.

FITTING PISTON RINGS

Note. See ENGINE OVERHAUL PROCEDURES article in ENGINE section for measuring piston ring side clearance and end gap.

1. Ensure manufacturer's marks face up when rings are installed. DO NOT use ring expander on side rails. Use ring expander to install intermediate and upper rings. Ensure ring gaps are staggered at proper intervals (Scheme 8)
2. If new piston rings are to be installed and no visible cross-hatch marks remain on cylinder walls, remove cylinder wall glaze using spring-type hone. After honing, clean bore and block with hot soapy water and oil cylinder walls.

1. Mark pistons and pins to assure assembly with same rod. Press piston pin from piston and connecting rod using Piston Pin Remover/Installer Set (J-24086).
2. Inspect and replace any piston pin showing signs of fracture, etching or wear. Check piston pin diameter.
3. Check piston pin-to-piston pin hole fit. If clearance exceeds specification, replace both piston and piston pin. See ENGINE SPECIFICATIONS table. Piston and pin are a matched set and are not available separately.

1. Raised notch on rod must face opposite notch on top of piston. Press pin through both piston and rod until pilot hub bottoms on support fixture and/or pin is centered in piston.
2. After pilot hub bottoms, DO NOT exceed 5000 lbs. (2275 kg) pressure with press. Ensure piston floats during pin installation operation.

CONNECTING ROD BEARINGS

Note. Precision insert bearings are used in this engine and shimming is not acceptable for adjustment. Always replace bearings in pairs. DO NOT file or grind connecting rods or caps when fitting bearings.

1. Remove connecting rod bearing caps and mark rods and caps for proper installation. Inspect each bearing for peeling, melting, seizure or improper contact. Replace defective bearings.
2. Measure outside diameter of crankshaft connecting rod bearing journals to determine if out-of-round or tapered. Replace crankshaft if measurement exceeds specification.
3. Use Plastigage method for bearing clearance check. See ENGINE OVERHAUL PROCEDURES article. NOTE: If clearance cannot be brought within specification using service bearings, replace crankshaft. DO NOT grind or recondition crankshaft. It is a rolled fillet type.
4. Check connecting rod side clearance. If excessive, replace connecting rod and cap. If side clearance is less than specification, remove rod and cap. Check for scratches, burrs, nicks or dirt between crankshaft and rod. Dress minor imperfections with oil stone. Recheck side clearance.
5. During assembly, ensure oil hole in bearing aligns with oil hole in connecting rod. Ensure bearing tangs are seated in appropriate slots in rod and cap. Ensure connecting rod bolt heads are properly seated in connecting rod.

MAIN BEARINGS

Note. Precision insert bearings are used in this engine and shimming is not acceptable for adjustment. Always replace bearings in pairs. DO NOT file or grind connecting rods or caps when fitting bearings.

1. Inspect each bearing for peeling, melting, seizure or improper contact. Replace defective bearings.
2. Measure outside diameter of crankshaft main bearing journals to determine if out-of-round or tapered. If measurement exceeds specification, replace crankshaft. See ENGINE SPECIFICATIONS at end of this section.
3. To check main bearing clearance, use Plastigage method. See ENGINE OVERHAUL PROCEDURES article. NOTE: If clearance cannot be brought within specification using service bearings, replace crankshaft. DO NOT grind or recondition crankshaft. It is a rolled fillet type.
4. If engine is in vehicle, position jack under counterweight adjoining bearing being checked, so weight of crankshaft will not compress Plastigage and provide an incorrect reading. DO NOT position jack under crankshaft pulley. Crankshaft post damage will result.
5. During assembly, ensure main bearing cap arrows face to front of engine.

CRANKSHAFT END PLAY

1. Tap the end of the crankshaft rearward and then forward with a lead hammer. This will line up the rear main bearing and crankshaft thrust surfaces. Tighten rear main bearing cap bolts to 65 ft. lbs. (88 N.m).
2. With the crankshaft forced forward, measure at the front end of the rear main bearing with a feeler gage. See ENGINE SPECIFICATIONS at end of this section.

REAR MAIN BEARING OIL SEAL

Note. Rear main bearing oil seal can be removed and installed without removal of oil pan or crankshaft.

Remove transmission assembly. On manual transmission, remove pressure plate and clutch disc. Remove flywheel retaining bolts and flywheel. Using screwdriver, pry out rear main bearing oil seal. Be careful not to scratch crankshaft or seal surface. Clean block-to-seal mating surface.

Coat outside surface of new seal with engine oil. Using Installer (J-34924), install seal with lip toward engine. Ensure that seal is firmly in place. Install flywheel. On manual transmission, install pressure plate and clutch disc. Install transmission.

Disconnect negative battery cable. Drain engine coolant. Remove drive belt, fan and fan clutch. Remove lower radiator hose at water pump. Remove water pump attaching bolts and remove water pump.

If installing new pump, transfer pulley from old pump. Apply continuous bead of sealer to clean pump sealing surface. Install water pump while sealer is still wet. Tighten bolts to specification. Install lower radiator hose. Install pulley and fan. Tighten bolts to specification. Install drive belt. Connect negative battery cable. Fill cooling system and check for leaks.

Note. For further information on cooling systems, see ENGINE COOLING SYSTEMS at end of this section.

CRANKCASE CAPACITY

Crankcase capacity is 3. qts. (2.8L). With oil filter change; 3.5 qts. (3.3L).

NORMAL OIL PRESSURE

Normal oil pressure is 36-41 psi (2.53-2.88 kg/cm 2 ) at 2000 RPM.

OIL PRESSURE REGULATOR VALVE

Oil pressure regulator valve is located in oil pump body. Valve is nonadjustable.

ENGINE OILING SYSTEM

Oil pump draws oil from pan, feeding it through oil filter and into passage along right side of block where it intersects lifter bosses. Oil is then routed to camshaft and crankshaft bearings through smaller drilled passages.

Oil is supplied to rocker arms through hydraulic lifters and push rods. By-pass valves are located in pick-up screen, oil filter mounting and oil pump. Oil returns to pan through return holes in head and block.

Remove oil pan. See OIL PAN REMOVAL article in ENGINE section. Remove oil pump attaching bolts and pick-up tube nut. Remove oil pump. Inspect oil pump pick-up tube for looseness. If the tube is loose, the oil pump must be replaced. A loose pickup tube can result in an air leak and loss of oil pressure.

1. Align oil pump shaft with the tank on the oil pump drive shaft. Position the oil pump over the oil pump drive shaft lower bushing. No gasket is used. The oil pump should slide easily into place.
2. Replace oil pump bolts and pick-up tube nut and tighten to specifications. See ENGINE SPECIFICATIONS table. To complete installation, reverse removal procedure. (Scheme 9)

Scheme 9

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

VALVE & VALVE SPRINGS SPECIFICATIONS

VALVE & VALVE SPRINGS SPECIFICATIONS

PISTON/PIN/RING SPECIFICATIONS

PISTONS, PINS & RINGS SPECIFICATIONS

BEARING SPECIFICATIONS

CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECS

CONNECTING RODS SPECIFICATIONS

CONNECTING RODS SPECIFICATIONS

CYLINDER HEAD SPECIFICATIONS

CYLINDER HEAD SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

VALVE LIFTERS SPECIFICATIONS

VALVE LIFTER SPECIFICATIONS

See also:
• ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION
• TORQUE SPECIFICATIONS