2.5l 4-cyl - Vins [a,e] GMC Sonoma Syclone

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 can be identified by eighth character of Vehicle Identification Number (VIN). VIN is stamped on a metal tag on top left end of instrument panel, near windshield. See ENGINE IDENTIFICATION table.

Engine can also be identified by engine identification (ID) number, stamped on front of cylinder block, immediately forward of right cylinder head or on left side of cylinder block on the engine-to-transmission mounting flange.

ENGINE IDENTIFICATION CODES

VALVE CLEARANCE ADJUSTMENT

Valve clearance is nonadjustable. Engine is equipped with hydraulic valve lifters.

FUEL PRESSURE RELEASE

Note. For reassembly reference, label all electrical connectors, vacuum hoses and fuel lines before removal. Also, place mating marks on engine hood and other assemblies before removal.

Loosen fuel tank filler cap to release tank pressure. Disconnect 3-wire electrical connector at fuel tank. Operate engine until it stalls. Crank engine for an additional 3 seconds. Turn ignition off. Connect 3-wire electrical connector.

ENGINE

1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae__fuel-pressure-release) . Remove hood. Disconnect negative battery cable. Drain cooling system.
2. Remove power steering reservoir from fan shroud (if equipped). Remove upper fan shroud, fan and radiator. Remove A/C compressor and power steering pump (if equipped) with hoses connected and lay aside. Remove air cleaner.
3. Remove fuel line bracket near fuel filter. Disconnect electrical connectors, vacuum lines, fuel lines and control cables as necessary. Disconnect heater hoses.
4. Remove strut rod. Disconnect exhaust pipe from converter hanger and exhaust manifold. Remove flexplate/flywheel cover, drive belt splash shield (if equipped) and starter. Remove flexplate-to-converter bolts (A/T). Remove 2 outer air dam bolts (left side).
5. Remove lower fan shroud. For access to upper transmission-to-engine bolts, remove body-to-chassis mounting bolts (left side), raise left side of body and support with wood blocks. Remove upper transmission-to-engine bolts. Lower body.
6. Remove remaining transmission-to-engine bolts. Remove motor mount through bolts. Lower vehicle. Support transmission. Pull engine forward slightly and turn sideways. Remove engine. To install, reverse removal procedure. Fill cooling system.

INTAKE MANIFOLD

1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae__fuel-pressure-release) . Disconnect negative battery cable. Remove air cleaner. Disconnect electrical connectors, vacuum lines, fuel lines and control cables as necessary.
2. Remove emissions sensor bracket from intake manifold. Drain cooling system. Disconnect water pump by-pass hose from intake manifold. Remove rear bracket from alternator. Disconnect heater hose from intake manifold. Remove intake manifold.
3. To install, reverse removal procedure using new intake manifold gasket. Tighten intake manifold bolts to 25 ft. lbs. (34 N.m). Fill cooling system.

EXHAUST MANIFOLD

1. Disconnect negative battery cable. Remove air cleaner assembly and heat stove tube. Remove A/C compressor (if equipped) and brackets with hoses connected and lay aside.
2. Remove oil dipstick tube bracket bolt. Disconnect oxygen sensor electrical connector. Disconnect exhaust pipe from manifold. Remove exhaust manifold.
3. To install, reverse removal procedure using new exhaust manifold gasket. Tighten exhaust manifold bolts in sequence. (Scheme 1) Tighten bolt Nos. 1, 2 and 7 to 36 ft. lbs. (49 N.m). Tighten bolt Nos. 3, 4, 5 and 6 to 32 ft. lbs. (43 N.m).

Scheme 1

Removal

1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae__fuel-pressure-release) . Disconnect negative battery cable. Drain cooling system. Remove air cleaner.
2. Remove A/C compressor (if equipped) and brackets with hoses connected and lay aside. Remove rocker arm cover. Loosen rocker arm nuts, rotate rocker arms to one side and remove push rods.
3. Disconnect electrical connectors, vacuum lines, fuel lines and control cables as necessary. Remove alternator and brackets. Disconnect water pump by-pass hose and heater hose from intake manifold. Disconnect exhaust pipe from exhaust manifold.
4. Remove upper radiator hose. Remove fuel filter and fuel line bracket from rear of cylinder head. Remove dipstick tube. Remove cylinder head bolts and cylinder head.

Installation

1. Clean cylinder head bolt threads and cylinder block holes. Apply thread sealing compound (1052080) to cylinder head bolt No. 9. Install gasket over dowel pins and ensure all holes align with cylinder block.
2. Install cylinder head with all bolts finger tight. Tighten all bolts in sequence to 18 ft. lbs. (24 N.m). (Scheme 2) Then tighten all bolts EXCEPT bolt No. 9 to 26 ft. lbs. (35 N.m). Tighten bolt No. 9 to 18 ft. lbs. (24 N.m).
3. Repeat sequence, tightening all bolts an additional 1/4 turn (90 degrees). To install remaining components, reverse removal procedure. Tighten rocker arm bolts with lifter on base circle of camshaft. Fill cooling system.

Scheme 2

Disconnect negative battery cable. Remove serpentine drive belt. Remove crankshaft damper hub bolt. Remove pulley and hub using puller. Replace hub if oil seal contact area is grooved or rough. Carefully pry out front crankshaft seal using large screwdriver ( DO NOT distort timing gear cover).

Coat seal-to-hub sealing lip with oil. Install seal using Seal Installer (J-34995). Tighten crankshaft damper hub bolt to 160 ft. lbs. (217 N.m). To complete installation, reverse removal procedure.

TIMING GEARS & CAMSHAFT

Note. Camshaft gear is pressed onto camshaft. Camshaft gear and camshaft must be removed as an assembly.

1. Disconnect negative battery cable. Remove power steering reservoir from fan shroud (if equipped). Remove upper fan shroud. Remove serpentine drive belt, fan and water pump pulley. Remove crankshaft pulley and damper hub.
2. Remove timing gear cover. Remove distributor. Remove cover plate, bearing and oil pump drive shaft and gear assembly from right side of cylinder block. (Scheme 3) Remove hydraulic valve lifters. See «HYDRAULIC VALVE LIFTERS»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae).
3. Remove radiator. Discharge A/C refrigerant and remove A/C condenser. Remove grille. Rotate crankshaft until thrust plate screws are visible through holes in camshaft gear. Remove thrust plate screws, thrust plate and spacer ring. Remove camshaft.

Inspection

1. Measure camshaft end play. If end play exceeds .005" (.13 mm), replace thrust plate. If end play is less than .0015" (.038 mm), replace spacer ring.
2. Measure journal diameter and out-of-round. If journal diameter is not 1.869" (47.47 mm) or out-of-round exceeds .001" (.03 mm), replace camshaft.

Coat camshaft lobes and journals with engine oil supplement. Install camshaft, ensuring timing marks on camshaft gear and crankshaft gear are aligned. To install remaining components, reverse removal procedure. Fill cooling system. Evacuate and charge A/C refrigerant system.

Scheme 3

1. Disconnect negative battery cable. Drain cooling system. Remove lower radiator hose and water pump by-pass hose. Remove alternator and bracket. Remove spark plug wires and bracket from intake manifold.
2. Remove fuel line bracket bolt from side cover. Remove oil pressure sending unit. Remove wiring harness brackets from side cover. Remove 4 nuts from side cover studs. Reverse and reinstall 2 nuts onto 2 inner studs. Install 2 remaining nuts onto same inner studs.
3. Using 2 wrenches, hold inner nut stationary. Jam 2 nuts tightly together. Using a wrench on inner nut, alternately unscrew studs until side cover breaks loose. Remove jammed nuts from studs. Remove studs from side cover.

Clean side cover-to-cylinder block sealing surfaces. Replace damaged studs and rubber washers. Tighten studs to 90 INCH lbs. (10 N.m). Apply a 3/16" diameter (5 mm) bead of RTV sealant to side cover. Install side cover. To complete installation, reverse removal procedure. Tighten side cover studs/nuts to 90 INCH lbs. (10 N.m). Fill cooling system.

1. Disconnect negative battery cable. Remove air cleaner, PCV valve and crankcase ventilation pipe. Remove EGR valve. Disconnect vacuum lines as necessary. Remove spark plug wires and clip from cover. CAUTION: To prevent sealing surface damage, DO NOT pry rocker arm cover from cylinder head.
2. Remove rocker arm cover bolts. Install Rocker Arm Cover Remover (J-34144-A) in place of each rocker arm cover bolt. Rotate rocker arm cover remover until rocker arm cover is lifted from cylinder head. Remove rocker arm cover.
3. Mark component location for reassembly reference. Remove rocker arm bolt and ball. Remove rocker arm, push rod and guide.

1. If installing new rocker arms or balls, coat components with Molykote. Install push rod guides, push rods, rocker arms, balls and rocker arm bolts. Ensure push rods seat in lifters. Tighten rocker arm bolt to 22 ft. lbs. (30 N.m) with lifter on base circle of camshaft lobe.
2. Apply a 3/16" (5 mm) diameter bead of RTV sealant to rocker arm cover, inboard of bolt holes. DO NOT allow sealant to enter rocker arm cover bolt holes in cylinder head. Install rocker arm cover. Tighten rocker arm cover bolts to 75 INCH pounds (8 N.m). To install remaining components, reverse removal procedure.

1. Remove rocker arms and push rods. See «ROCKER ARMS & PUSH RODS»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae). Remove push rod side cover. See PUSH ROD SIDE COVER.
2. Remove lifter retainer, guide and lifter. (Scheme 4) Mark component location for reassembly reference.

Scheme 4

Measure lifter diameter and lifter bore diameter. Determine lifter oil clearance. Replace lifter if oil clearance is not within specification. See VALVE LIFTERS table under ENGINE SPECIFICATIONS .

Lubricate lifter surfaces with oil and install in bore. To install remaining components, reverse removal procedure. Tighten lifter retainer stud to 90 INCH lbs. (10 N.m).

1. Disconnect negative battery cable. Remove power steering fluid reservoir from fan shroud (if equipped). Remove upper fan shroud. Raise and support vehicle. Drain crankcase. Remove strut rods.
2. Disconnect exhaust pipe from manifold and catalytic converter as necessary. Remove flywheel/flexplate cover, starter and brace. Disconnect brake line bracket from crossmember. Remove front engine mount bolts. Remove oil pan.

1. Apply a bead of RTV sealant to sealing surface of oil pan (inboard of oil pan bolt holes), rear main bearing cap-to-cylinder block junction and front cover-to-cylinder block junction. Install oil pan.
2. Tighten oil pan bolts to 90 INCH lbs. (10 N.m). To install remaining components, reverse removal procedure.

Removal & Disassembly

1. Remove oil pan. See «OIL PAN»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae). Remove oil pump bolts and pick-up tube nut. Remove oil pump.
2. Remove oil pump cover screws, cover and gasket. (Scheme 5) Mark gear teeth for reassembly reference. Remove drive gear and shaft. Remove idler gear. Remove spring retainer, pressure regulator spring and pressure regulator valve.

1. Replace oil pump if pick-up tube is loose. Ensure pressure regulator valve slides freely in its bore. With gears removed, measure gear length and diameter, and gear pocket depth and diameter.
2. Install gears. Measure gear lash, side clearance and end clearance. Replace oil pump if any measurements are not within specification. See «OIL PUMP SPECIFICATIONS»(/gmc/sonoma-syclone/1991-1992/remont/mechanical/#25l-4-cyl-vins-ae) table.

Scheme 5

OIL PUMP SPECIFICATIONS

Reassembly & Installation

To reassemble, reverse disassembly procedure. Align marks on gears when installing in pump body. Tighten pump cover screws to 10 ft. lbs. (14 N.m). To install, reverse removal procedure. Tighten oil pump bolts to 18 ft. lbs. (24 N.m). Tighten pick-up tube nut to 22 ft. lbs. (30 N.m).

Remove transmission and flywheel/flexplate. See appropriate AUTOMATIC TRANSMISSION SERVICING article (A/T) or CLUTCHES article (M/T). Note direction of seal for installation. Carefully pry seal from housing. DO NOT scratch sealing surface on crankshaft outer diameter.

Coat inner and outer seal surfaces with engine oil. Using Seal Installer (J-34924), install seal. To install remaining components, reverse removal procedure.

Drain cooling system. Remove serpentine belt. Remove upper fan shroud, fan/clutch assembly and water pump pulley. Disconnect hose(s) from water pump. Remove water pump bolts and water pump.

To install, reverse removal procedure. Apply Sealant (1052080) to water pump bolt threads. Tighten water pump bolts to 22 ft. lbs. (30 N.m). Fill cooling system.

VALVE SPRINGS

Replace valve spring if free length, installed height and pressure are not within specification. See VALVES & VALVE SPRINGS table under ENGINE SPECIFICATIONS.

VALVE STEM OIL SEALS

1. Valve stem uses an upper "O" ring seal and a lower cone seal. To install valve stem oil seals, slide cone seal over valve stem until seated against cylinder head. Install spring/damper, shield and cap. Apply engine oil to "O" ring seal.
2. Compress valve spring. Install "O" ring seal in groove in valve stem, ensuring seal is not twisted. Install keepers (hold in place with grease if necessary). Decompress valve spring.
3. To test valve seal, lightly wet the suction cup on Valve Stem Seal Tester (J-22330) with oil. Place suction cup on top of cap. Press on tester to create vacuum. If cup will not hold vacuum, seal is damaged or installed incorrectly.

VALVE GUIDES

Valve guides are part of cylinder head (not replaceable). If valve stem-to-guide clearance is not .0010-.0025" (.025-.064 mm) on intake valves and .0013-.0030" (.033-.076 mm) on exhaust valves, ream valve guide and install oversized valve. Oversized intake valves are available in .003" (.08 mm) and .005" (.13 mm). Oversized exhaust valves are available in .003" (.08 mm).

VALVE SEATS

Valve seats are induction hardened. DO NOT remove an excessive amount of material from seat.

VALVES

Replace valve if margin is less than 1/32" (.8 mm).

HYDRAULIC VALVE LIFTER

1. To disassemble, press down on push rod seat with screwdriver and remove retainer. (Scheme 6) Remove push rod seat, metering valve, plunger and plunger spring (if plunger is stuck, turn lifter upside down and tap against flat surface to dislodge).
2. Using small screwdriver, pry check ball retainer from plunger. Remove check ball spring and check ball from plunger. Remove plunger spring from lifter body. CAUTION: DO NOT interchange parts between lifters.
3. To assemble, turn plunger upside-down. Insert check ball, check ball spring and check ball retainer into plunger. Slide plunger spring over check ball retainer.
4. Insert plunger into lifter body, aligning oil feed holes in lifter body and plunger. Turn lifter upright. Fill lifter with 10W oil.
5. Insert end of 1/8" (3 mm) drift punch into top of plunger and press down firmly ( DO NOT force or pump plunger). Insert a 1/16" (1.5 mm) drift punch through both oil holes to hold plunger down against spring pressure. Remove 1/8" (3 mm) drift punch.
6. Refill lifter with 10W oil. Install metering valve, push rod seat and retainer. Push down on push rod seat using a push rod. Remove 1/16" (1.5 mm) drift punch.

Scheme 6

PISTON & ROD ASSEMBLY

Mark piston position in relation to connecting rod before separating components. Install piston in cylinder block with mark on top of piston toward front of engine.

FITTING PISTONS

Measure piston diameter at 90-degree angle to piston pin bore, on center line of piston pin bore (1 13/16" below top of piston). Measure cylinder bore diameter 2.25" (57.2 mm) from cylinder block deck surface.

PISTON RINGS

Install piston rings with end gaps properly spaced around circumference of piston. (Scheme 7)

Scheme 7

ROD BEARINGS

Undersized bearings are available in .001" (.025 mm).

CRANKSHAFT & MAIN BEARINGS

Mark main bearing caps for reassembly reference. Undersize bearings are available in .001" (.025 mm).

THRUST BEARING

Rear main bearing is thrust bearing. To measure crankshaft end play, tighten main bearing cap bolts to 10 ft. lbs. (14 N.m). Tap end of crankshaft rearward then forward with lead hammer to align rear main bearing and crankshaft thrust surfaces. Tighten main bearing cap bolts to 65 ft. lbs. (88 N.m). Measure end play between front end of rear main bearing cap and crankshaft.

CYLINDER BLOCK

If cylinder block deck surface warpage exceeds .004" (.10 mm), machine surface. Replace cylinder block if more than .010" (.25 mm) material is removed from deck surface.

DESCRIPTION

Oil pump is gear-driven from camshaft. (Scheme 8) 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 cylinder head and cylinder block.

CRANKCASE CAPACITY

Oil capacity is approximately 3.5 qts. (3.3L) with filter change.

OIL PRESSURE

Oil pressure is 36-41 psi (2.53-2.88 kg/cm 2 ) at 2000 RPM at normal operating temperature.

Scheme 8

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

BEARING SPECIFICATIONS

MAIN & CONNECTING ROD BEARINGS SPECS

CONNECTING ROD SPECIFICATIONS

CONNECTING ROD SPECIFICATIONS

PISTON/PIN/RING SPECIFICATIONS

PISTONS, PINS & RINGS SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

VALVE/VALVE SPRING SPECIFICATIONS

VALVES & VALVE SPRINGS SPECIFICATIONS

CYLINDER HEAD SPECIFICATIONS

CYLINDER HEAD SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

VALVE LIFTERS SPECIFICATIONS

VALVE LIFTERS SPECIFICATIONS

See also:
• ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION
• FUEL PRESSURE RELEASE
• HYDRAULIC VALVE LIFTERS