7.4l v8 - Vins [n,w] GMC Cab & Chassis R2500

ENGINE IDENTIFICATION

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

Engine can be identified by the eighth character of the Vehicle Identification Number (VIN). The VIN number is located on a metal tag on the top left corner of the 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 «VALVE CLEARANCE ADJUSTMENT»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table.
2. Loosen rocker arm adjusting nut until lash is present. Tighten adjusting nut until lash is removed and push rod will not rotate. Turn adjusting nut only 3/4 turn.
3. Rotate crankshaft 360 degrees to bring No. 6 piston to TDC of compression stroke. Adjust remaining valves. See «VALVE CLEARANCE ADJUSTMENT»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table.

VALVE CLEARANCE ADJUSTMENT

ENGINE

See ENGINE REMOVAL article.

ENGINE OVERHAUL

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

Removal

1. Disconnect negative battery cable. Remove air cleaner. Drain cooling system. On van models, remove engine cover. Remove air injection crossover hose.
2. Remove heater and radiator hose. Remove alternator bracket. Label and disconnect necessary wires and hoses. Disconnect necessary fuel lines and linkages.
3. Remove distributor cap and mark position of rotor with chalk. Remove distributor. Remove A/C compressor and bracket (if equipped). Remove brake vacuum pipe. Remove manifold bolts and intake manifold.

Installation

Install gasket clips (if equipped). Install gaskets on cylinder heads. Install seals on cylinder block. Install intake manifold. Install manifold retaining bolts. Tighten bolts in sequence. (Scheme 34) Tighten bolts to specification. To complete installation, reverse removal procedure.

Scheme 34

Remove heat stove tube. Remove all attached brackets and heat shields. 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 and tighten attaching bolts to specification. Bend over lock tabs (if equipped). To complete installation, reverse removal procedure.

1. Disconnect negative battery cable. Drain cooling system, including block. Remove intake and exhaust manifolds. Remove A/C compressor and bracket (if equipped). Disconnect wiring and hoses from cylinder heads. Remove alternator, spark plugs and valve covers.
2. 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.

Cleaning & Inspection

Clean cylinder head and inspect. For complete cleaning and inspection see ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article.

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 35) 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»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) under ADJUSTMENTS.

Scheme 35

ROCKER ARM STUDS

Rocker arm studs are threaded in cylinder head. Rocker arm studs retain the 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 & OIL SEALS

See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article for removal and installation procedures. Valve spring free length and tension should be checked prior to installation. See VALVE SPRING SPECIFICATIONS table under ENGINE SPECIFICATIONS for specifications.

VALVE SPRING INSTALLED HEIGHT

Installed valve spring height must be checked. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article. If installed height exceeds specifications, shim to meet specifications. See SPRING INSTALLED HEIGHT SPECIFICATIONS table.

SPRING INSTALLED HEIGHT SPECIFICATIONS

VALVE GUIDES

Check valve stem-to-guide clearance. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article. Oversize valves must be used if not within specification. See VALVE SPECIFICATIONS table 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-23523-E), remove vibration damper. Remove all mounting brackets and coolant hoses attached to water pump. Remove water pump, 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. Install vibration damper using damper puller/installer.
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.

Remove drive belts. Remove vibration damper retaining bolt. Using Damper Puller/Installer (J-23523-E), 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 the engine. Coat seal lip with engine oil. Install vibration damper.
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.

Remove engine front cover. See ENGINE FRONT COVER . Crank engine over until timing marks on camshaft and crankshaft sprockets are aligned. 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 36) Install and tighten sprocket bolts to specification. Reverse removal procedure to install remaining components. Tighten all bolts to specification.

Scheme 36

1. Remove intake manifold, engine front cover, timing chain and camshaft sprocket. Remove valve covers. Loosen all rocker arm nuts and rotate rockers to one side. Remove push rods and lifters. Mark for location for reassembly reference.
2. Remove radiator and grille. Remove fuel pump and push rod for carbureted engines. Remove camshaft.

Clean all components with clean solvent. Inspect camshaft lobes for signs of flaking or flat spots. Measure camshaft journal O.D. and runout. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article. Replace camshaft if not within specification. See CAMSHAFT SPECIFICATIONS table under ENGINE SPECIFICATIONS.

1. Coat camshaft lobes and journals with engine oil supplement. Install 3 bolts in front of camshaft for ease in handling. Install camshaft. Tighten to specification.
2. Temporarily place camshaft sprocket on camshaft and align timing marks. Install camshaft sprocket and chain. Tighten camshaft sprocket attaching 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»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) under ADJUSTMENTS.

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 the 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 SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table under ENGINE SPECIFICATIONS. Replace camshaft and lifters if not within specification.

1. Remove oil pan, oil pump, crankshaft and camshaft. Move pistons upward to top of cylinder bores. Using Bearing Remover/Installer (J-6098-01), remove camshaft bearings. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article.
2. Install front and rear camshaft bearings first, to act as guides for remover/installer pilot. Ensure that bearing 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 PAN REMOVAL article.

Remove intake manifold and cylinder head. See INTAKE MANIFOLD and CYLINDER HEAD . Remove oil pan and oil pump. Ensure that rods and rod caps are marked for cylinder location. Remove cylinder ridge and piston and rod assembly. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article.

See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article for complete cleaning and inspection.

Scheme 37

1. For installation, end clearance and side clearance checking procedure see «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Properly position rings on piston. (Scheme 37) Valve clearance notch must face the top of cylinder block.
2. Check connecting rod side clearance. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Connecting rod side clearance must be within specification. See «CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table under ENGINE SPECIFICATIONS. Ensure crankshaft turns smoothly.

FITTING PISTONS

Determine cylinder taper, wear and out-of-roundness and piston clearance. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article. For cylinder specifications, see CYLINDER & PISTON WEAR SPECIFICATIONS table. If taper or out-of-round are not within limits, hone or bore cylinders for installation of new pistons.

CYLINDER & PISTON WEAR SPECIFICATIONS

FITTING RINGS

Check piston ring end gap and side clearance to prevent ring damage. See ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION article. If ring gap is not within specifications, try another ring set. See PISTONS, PINS & RINGS SPECIFICATIONS table 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 SPECIFICATIONS table 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. 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. Crankshaft out-of-round or taper must not exceed .001" (.03 mm).
3. Measure bearing clearance using Plastigage method. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Install new bearings and tighten rod cap to specification. See «CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table 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. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Side clearance should be within specification. See «CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table under ENGINE SPECIFICATIONS.

CRANKSHAFT MAIN BEARINGS

1. Ensure that crankshaft and cylinder block is clean. Install upper main bearings in cylinder block. Ensure that tang and oil holes align on bearing with cylinder block.
2. Carefully install crankshaft. Check bearing clearance using Plastigage method. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Install lower main bearings and caps. Ensure that bearing caps are installed in proper location. Tighten bearing caps to specification. See «TORQUE SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw__torque-specifications) .
3. Once bearing clearance is checked, remove caps and coat bearing and journals with engine oil. Install all bearing caps except rear bearing cap. Thrust bearing alignment must be set to provide proper operation. Tighten main cap bolts to specification. Crankshaft end play must be checked.

CRANKSHAFT END PLAY

1. Ensure all other main bearing caps have been properly tightened. Apply oil sealing compound to mating surface of bearing cap and cylinder block at split line. Sealant must not contact crankshaft or rear seal.
2. Install and tighten rear main bearing cap bolts to 10 ft. lbs. (14 N.m). Tap crankshaft rearward, then forward. Tighten rear main bearing cap to specification.
3. Pry crankshaft toward front of engine and check crankshaft end play. See «ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION»(/gmc/cab-chassis-r2500/1987-1987/remont/engine/#engine-overhaul-procedures-general-information) article. Check for proper thrust bearing if end play is not within specification. See «CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/mechanical/#74l-v8-vins-nw) table under ENGINE SPECIFICATIONS.

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 38

1. Fabricate an oil seal installer if not supplied with replacement oil seal. (Scheme 38) Seal must be installed with oil lip facing front of engine. Use fabricated installer to protect seal from sharp edges.
2. Install seal in main bearing cap. Coat seal lip with engine oil. Do not allow oil to contact ends of oil seal. Position upper seal with seal lip facing front of engine. Install 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 oil sealing compound 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.

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 SYSTEM article.

CRANKCASE CAPACITY

Crankcase capacity is 6 qts. (5.7L). Add one qt. (.95L) when replacing oil filter.

OIL FILTER

Replace oil filter at every oil change.

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. (Scheme 39)

Scheme 39

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. (Scheme 39)

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. See TORQUE SPECIFICATIONS .

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. See TORQUE SPECIFICATIONS . Install oil pan.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

VALVE SPECIFICATIONS

VALVE SPECIFICATIONS

PISTON/PIN/RING SPECIFICATIONS

PISTONS, PINS & RINGS SPECIFICATIONS

BEARING SPECIFICATIONS

CRANKSHAFT MAIN & CONNECTING ROD BEARINGS SPECIFICATIONS

VALVE SPRING SPECIFICATIONS

VALVE SPRINGS SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

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