7.4l v8 - Vins [n,w] GMC Magnavan G3500

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 located on a metal tag on top left corner of instrument panel. Engine identification number is stamped on a machined pad on front of cylinder block, immediately forward of right cylinder head.

ENGINE IDENTIFICATION CODES

Valve Arrangement

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

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

1. Rotate engine until No. 1 piston is on TDC of compression stroke. With piston in this position, adjust valves listed in appropriate VALVE CLEARANCE ADJUSTMENT table.
2. Loosen rocker arm adjusting nut until lash is present. Tighten adjusting nut until lash is removed and push rod will not rotate. When lash is removed, turn adjusting nut only 3/4 turn.
3. Rotate crankshaft 360 degrees to bring No. 6 piston to TDC. Adjust remaining valves. See VALVE CLEARANCE ADJUSTMENT table.

VALVE CLEARANCE ADJUSTMENT

TROUBLE SHOOTING

Note. See TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

ENGINE OVERHAUL

Note. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article for basic procedures not covered in this article.

Removal

1. Place transmission gear selector in park (neutral on manual transmissions). Set parking brake and block drive wheels.
2. Disconnect negative battery cable. On Van models, remove engine cover and air injection crossover hose. On all models, remove air cleaner. Drain cooling system. Label and disconnect necessary brackets, wires and hoses. Disconnect fuel lines and linkages.
3. Remove distributor cap. With chalk or crayon, mark relationship of distributor rotor and housing to a stationary reference point in engine compartment. Remove distributor. DO NOT rotate crankshaft while engine is apart.
4. Remove brake booster vacuum pipe. Remove A/C pump bracket and alternator bracket. Remove carburetor or throttle body (if necessary). Remove manifold bolts. Remove intake manifold and gaskets. (Scheme 16)

Installation

1. Install front and rear seals on cylinder block. (Scheme 16) Install gaskets on cylinder heads. Install intake manifold. Install manifold retaining bolts. Tighten bolts in sequence to specification. (Scheme 17) To complete installation, reverse removal procedure.

Scheme 16

Scheme 17

Remove heat stove tube. Remove all attached brackets and heat shields. On some models, it may be necessary to remove dip stick tube. Disconnect oxygen sensor wire. Disconnect exhaust pipe from manifold. Bend over lock tabs (if equipped). Remove retaining bolts and exhaust manifold.

Clean all mating surfaces. Install manifold. Tighten bolts to specification. Bend over lock tabs (if equipped). To complete installation, reverse removal procedure.

1. Place transmission gear selector in park (neutral on manual transmissions). Set parking brake and block drive wheels. Although fuel pressure drops to zero when ignition is turned off, loosen fuel filler cap to relieve tank pressure. To further minimize risk of fire and personal injury, cover surrounding areas with a shop rag while removing fuel lines. WARNING: To avoid possible personal injury and fire danger, fuel pressure must be relieved as outlined in step 1).
2. Disconnect negative battery cable. Drain cooling system, including block. Remove intake and exhaust manifolds as previously described. Remove A/C compressor and bracket (if equipped). Disconnect wiring and hoses from cylinder heads. Remove alternator, spark plugs and valve covers.
3. Loosen rocker arm nuts and rotate rocker arms to side. Remove push rods in sequence and mark for reassembly in original locations. Remove cylinder head bolts. Remove cylinder heads.

1. Clean all gasket surfaces and head bolt holes. On steel head gaskets apply thin coat of sealer to both sides of gasket. Do not use sealer on steel/asbestos gaskets.
2. Position gaskets on cylinder block with bead facing upward. Ensure that all holes align. Install cylinder heads. Coat threads of head bolts with Sealant (1052080).
3. Install and tighten head bolts in sequence. (Scheme 18) Tighten head bolts to specification. To complete installation, reverse removal procedure. Lubricate valve tip, rocker arm pivot and push rod socket with Molykote prior to installation. Adjust valves. See VALVE CLEARANCE ADJUSTMENT.

Scheme 18

ROCKER ARM STUDS

Rocker arm studs are threaded into cylinder head. Rocker arm studs retain push rod guide.

Removal & Installation

Remove threaded rocker arm stud using proper socket. Remove push rod guide. Install new rocker arm studs and push rod guide. Tighten rocker arm stud to specification.

VALVE SPRINGS

Valve spring free length and tension should be checked prior to installation. See VALVE & VALVE SPRINGS under ENGINE SPECIFICATIONS for specifications.

VALVE SPRING INSTALLED HEIGHT

Installed valve spring height must be checked. If installed height exceeds specifications, shim to meet specifications. See VALVES & VALVE SPRINGS under ENGINE SPECIFICATIONS tables.

VALVE GUIDES

Check valve stem-to-guide clearance. Oversize valves must be used if not within specification. See CYLINDER HEAD under ENGINE SPECIFICATIONS. Valves with oversize stems are available.

1. Disconnect negative battery cable at battery. Drain cooling system. If necessary, remove radiator shroud. Remove all accessory drive belts, fan and pulley.
2. Remove vibration damper retaining bolt. Using Damper Puller/Installer (J-39046), remove vibration damper. Remove all mounting brackets and coolant hoses attached to water pump. Remove water pump. Loosen or remove oil pan as necessary for removal of front cover. Remove front cover bolts, front cover, timing tab (if equipped) and gasket.

1. Install gasket on front cover with gasket sealer. Install cover on engine block and timing tab (if equipped). Tighten bolts to specification. See «TORQUE SPECIFICATIONS»(/gmc/magnavan-g3500/1985-1993/remont/mechanical/#74l-v8-vins-nw__torque-specifications) . Install vibration damper using Damper Puller/Installer (J-39046).
2. Before installing vibration damper retaining bolt, apply small amount of RTV sealant at crankshaft Woodruff key and vibration damper. Install retaining bolt. Tighten to specification. Reverse removal procedure to install remaining components. Tighten bolts to specification. See «TORQUE SPECIFICATIONS»(/gmc/magnavan-g3500/1985-1993/remont/mechanical/#74l-v8-vins-nw__torque-specifications) .

Remove drive belts. Remove pulley. Remove vibration damper retaining bolt. Using Damper Puller/Installer (J-39046), remove vibration damper. Pry seal from cover with screwdriver. Do not damage front cover.

1. Using Seal Installer (J-22102), install new seal in front cover. Seal lip must face toward engine. Coat seal lip with engine oil. Install vibration damper using Damper Puller/Installer (J-39046).
2. Before installing vibration damper retaining bolt, apply small amount of RTV sealant at crankshaft Woodruff key and vibration damper. Install retaining bolt and tighten to specification. Reverse removal procedure to install remaining components. Tighten all bolts to specification. See «TORQUE SPECIFICATIONS»(/gmc/magnavan-g3500/1985-1993/remont/mechanical/#74l-v8-vins-nw__torque-specifications) .

Remove engine front cover. See ENGINE FRONT COVER. Crank engine over until timing marks on camshaft and crankshaft sprockets are aligned. (Scheme 19) Remove camshaft sprocket and timing chain. If crankshaft sprocket replacement is necessary, use Sprocket Puller (J-1619) to remove sprocket.

1. Install Woodruff key in crankshaft (if removed). Using Crankshaft Sprocket Installer (J-22102), install crankshaft sprocket on crankshaft. Install camshaft sprocket and timing chain.
2. Ensure timing marks on sprockets are aligned. (Scheme 19) Install and tighten camshaft sprocket bolts to specification. See «TORQUE SPECIFICATIONS»(/gmc/magnavan-g3500/1985-1993/remont/mechanical/#74l-v8-vins-nw__torque-specifications). Reverse removal procedure to install remaining components.

Scheme 19

1. Remove intake manifold, engine front cover, timing chain and camshaft sprocket as previously described. Remove valve covers. Loosen all rocker arm nuts and rotate rockers to one side. Remove push rods and lifters. Mark location for reassembly reference.
2. Remove radiator and grille. Reinstall cam gear for ease in handling. Remove camshaft.

Cleaning & Inspection

Clean all components with clean solvent. Inspect camshaft lobes for signs of flaking or flat spots. Measure camshaft. Replace camshaft if not within specification. See CAMSHAFT under ENGINE SPECIFICATIONS.

1. Coat camshaft lobes and journals with engine oil supplement. Install cam gear for ease in handling. Install camshaft. Tighten to specification.
2. Temporarily place camshaft sprocket on camshaft and align timing marks. Remove sprocket. Install camshaft sprocket and chain. Tighten camshaft sprocket bolts to specification.
3. Lubricate timing chain with engine oil. When installing new camshaft, install new lifters, change oil and filter. Reverse removal procedure to install remaining components. Tighten all bolts to specification. Adjust valves. See VALVE CLEARANCE ADJUSTMENT.

CAM LOBE LIFT

1. Remove valve cover and rocker arm assembly. Using Lobe Lift Indicator (J-8520), mount dial indicator on cylinder head. Position dial indicator and ball socket adapter on push rod.
2. Slowly rotate engine in direction of rotation until lifter is on base circle of camshaft. This is lowest reading. Adjust dial indicator to zero. Rotate engine until push rod is fully raised and note reading.
3. Compare reading with specification. See CAMSHAFT table under ENGINE SPECIFICATIONS. Replace camshaft and lifters if not within specification.

1. Remove engine. See ENGINE REMOVAL article. Remove oil pan, oil pump, flywheel, timing cover and chain. Remove crankshaft. Remove camshaft. Move pistons upward to top of cylinder bores. Using Bearing Remover/Installer (J-6098-01), remove camshaft bearings.
2. Install front and rear camshaft bearings first, to act as guides for remover/installer pilot. Ensure that bearing oil passages are aligned with oil passages in block. Use 3/32" diameter round stock to check oil passage alignment. Coat camshaft rear bore plug with sealer. Install plug even to 1/32" below engine block surface.

OIL PAN

See ENGINE OIL PAN REMOVAL article.

Remove intake manifold and cylinder head as previously described. Remove oil pan and oil pump. Ensure that rods and rod caps are marked for cylinder location. Remove cylinder ridge. Remove piston and rod assembly.

Scheme 20

1. Properly position rings on piston. (Scheme 20) Valve clearance notch must face lifter valley.
2. Check connecting rod side clearance. Connecting rod side clearance must be within specification. See ENGINE SPECIFICATIONS. Ensure crankshaft turns smoothly.

FITTING PISTONS

Determine cylinder taper, wear, out-of-round and piston clearance. For cylinder specifications see CYLINDER BLOCK and PISTONS, PINS & RINGS under ENGINE SPECIFICATIONS. If taper or out-of-round are not within limits, hone or bore cylinders for installation of new pistons.

FITTING RINGS

Check piston ring end gap and side clearance to prevent ring damage. If ring gap is not within specifications, try another ring set. See PISTONS, PINS & RINGS under ENGINE SPECIFICATIONS.

Piston pins are press-fit in connecting rod. Remove snap rings from piston. Using an arbor press, press piston pin from piston and connecting rod. Note location of piston notches or valve area in relation to rod bearing tangs.

Inspection

Measure piston pin diameter, piston pin bore diameter and connecting rod pin bore. Determine piston pin clearance for piston and connecting rod. Replace piston, piston pin or connecting rod if not within specification. See PISTONS, PINS & RINGS under ENGINE SPECIFICATIONS.

Lubricate piston pin holes in piston and connecting rod with engine oil. Install piston on connecting rod with valve areas opposite rod bearing tangs. Using arbor press, press piston pin into piston and connecting rod. Install snap rings. Check piston for freedom of movement on piston pin.

CONNECTING ROD BEARINGS

1. Prior to removal, ensure rod caps are marked for cylinder identification. Remove rod cap and bearings. Inspect bearings for wear or damage and replace as necessary.
2. Check crankshaft rod bearing journal for out-of-round or taper. See CRANKSHAFT, MAIN & CONNECTING ROD BEARINGS under ENGINE SPECIFICATIONS.
3. Measure bearing clearance using Plastigage method. See CRANKSHAFT MAIN & CONNECTING ROD BEARINGS under ENGINE SPECIFICATIONS for bearing clearance.
4. If clearance exceeds specifications, undersize bearings possibly can be used in combination to produce correct clearance. If clearance is still excessive, crankshaft must be reconditioned.
5. Clean crankshaft journal and bearing surface in rod. Insert bearings in rod and cap, then lubricate bearing surfaces with oil. Pull piston and rod assembly down onto crankshaft.
6. Install cap and tighten to specification. Check connecting rod side clearance. For specification, see CRANKSHAFT MAIN & CONNECTING ROD BEARINGS table under ENGINE SPECIFICATIONS.

MAIN BEARINGS

Note. Procedure listed describes main bearing removal and installation with engine in vehicle. Measure and change bearings one journal at a time if engine is in vehicle.

1. Remove oil pan. See OIL PAN REMOVAL. Remove bearing cap. Use Plastigage method to check bearing clearance.
2. Mark main bearing caps for identification so caps are replaced in same direction and location. Remove main bearings from cylinder block by inserting bearing Remover/Installer (J-8080) in crankshaft oil hole. Rotate crankshaft to "roll" bearing out. If remover/installer is unavailable, use a bent cotter pin.
3. To install upper bearing half, lubricate journal and bearing. Insert plain end of bearing (the end without bearing tang) between crankshaft and notched side of block. With bearing remover/installer in crankshaft oil hole, rotate crankshaft to install bearing.
4. Install lower bearing half into cap and lubricate with engine oil. Install and tighten main bearing cap with arrow pointing toward front of engine.

THRUST BEARING ALIGNMENT

1. Ensure all main bearing caps, except rear main (thrust) bearing, are installed and tightened to specification. Temporarily tighten rear main bearing cap bolts to 10 ft. lbs. (14 N.m).
2. Tap end of crankshaft back and forth to line up main bearing and crankshaft thrust surfaces. Tighten thrust bearing cap to specification. Retighten all main bearing cap bolts to specification, including thrust bearing. Rotate crankshaft to confirm free movement.

CRANKSHAFT END PLAY

With all main bearings installed and torqued to specification, pry crankshaft toward front of engine and check crankshaft end play. See CRANKSHAFT, MAIN & CONNECTING ROD BEARINGS under ENGINE SPECIFICATIONS.

Remove oil pan and oil pump. Remove rear main bearing cap and pry out old seal. Remove upper half of seal by tapping end with brass punch until seal protrudes enough to be removed with pliers.

Scheme 21

1. Fabricate an oil seal installer if not supplied with replacement oil seal. (Scheme 21) Seal must be installed with oil lip facing front of engine. Use fabricated installer to protect seal from sharp edges.
2. Coat seal lip with engine oil. Do not allow oil to contact ends of oil seal. Install lower seal in main bearing cap. Install upper seal. Using fabricated installer. Feed seal in cylinder block.
3. Roll seal around crankshaft. Use installer to protect seal from sharp corner of seal groove in cylinder block. Leave fabricated installer in position, until both ends of seal are flush with block.
4. Remove fabricated installer. Apply sealer on cap-to-block mating surface of cylinder block at split line. Do not allow sealant to contact rear oil seal or crankshaft. Install and tighten rear main bearing cap to specification. Install oil pump and oil pan.

Disconnect negative battery cable at battery. Drain cooling system. Remove all drive belts, coolant hoses and mounting brackets attached to water pump. If necessary, remove fan shroud. Remove fan and pulley. Remove water pump and gaskets.

Clean all gasket surfaces. Using new gaskets, install and tighten water pump bolts to specification. Install remaining components in reverse order of removal.

Note. For further information on cooling systems, see ENGINE COOLING SYSTEMS.

CRANKCASE CAPACITY

Crankcase capacity on 7.4L (VIN W) engine is 6 qts. (5.7L), on 7.4L (VIN N) engine capacity is 5 qts. (4.8L) and capacity is 4 qts. (3.8L) on all vans and other engine applications. Add one additional qt. (.95L) to all engines when replacing oil filter.

NORMAL OIL PRESSURE

Normal oil pressure should be obtained with engine at normal operating temperature and at specified engine RPM. See OIL PRESSURE SPECIFICATIONS table.

OIL PRESSURE SPECIFICATIONS

OIL PRESSURE REGULATOR VALVE

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

ENGINE OILING SYSTEM

Gear-type oil pump delivers full pressure lubrication to main oil gallery and through full-flow oil filter. Through drilled passages in block, main oil gallery feeds oil to all crankshaft and camshaft bearings.

Valve lifter oil gallery feeds lifters. From lifters, oil is routed through hollow push rods to upper valve train components. Timing chain and sprockets are lubricated by oil drainage from No. 1 camshaft bearing.

Remove oil pan. Remove pump-to-rear main bearing cap bolts. Remove pump and baffle (if equipped) and extension shaft.

Disassembly

Remove pump cover. If necessary, remove inlet tube and screen assembly. Mark gears at a meshing point, so they may be reassembled with same gear teeth indexing. Remove gears. Remove pressure regulator retaining pin. Remove washer (if equipped), pressure regulator valve and spring.

Inspect pump body and cover for cracks or excessive wear. Inspect pump gears for damage or wear. Check drive gear shaft for looseness in pump body. Check pressure regulator valve for fit in bore. Replace entire pump assembly if damaged. Inspect inlet tube and screen assembly for damage.

Reassembly

Install pump gears into pump body, with marked gear teeth indexing. Idler gear must be installed with smooth side of gear toward cover opening. If inlet tube was removed, apply sealer to end of inlet tube. Tap inlet tube into place using plastic hammer. Reassemble remaining components in reverse order of disassembly. Tighten cover screws to specification.

Prime oil pump with engine oil. Assemble pump and extension shaft to engine. Ensure slot on top of extension shaft engages with drive tang on end of distributor shaft. Install oil pump and baffle (if used). Tighten retaining bolt to specification. Install oil pan.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

GENERAL ENGINE 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

VALVE & VALVE SPRING SPECIFICATIONS

VALVE & VALVE SPRINGS SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

CYLINDER BLOCK SPECIFICATIONS

VALVE LIFTERS SPECIFICATIONS

VALVE LIFTER SPECIFICATIONS

See also:
• ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION
• ENGINE OIL PAN REMOVAL
• TORQUE SPECIFICATIONS
• ENGINE FRONT COVER