7.4l v8 - VIN [w] GMC Cab & Chassis S15

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 code number located on pad at front top center of engine block forward of intake manifold. The Vehicle Identification Number (VIN) is located on a metal plate on top left side of instrument panel, visible through windshield. Engine can be identified by the 8th character of the VIN.

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 timing marks are aligned and No. 1 cylinder is at TDC. Back off rocker arm adjusting nut on No. 1 intake and exhaust rocker arm until play in push rod is detected.
2. Tighten rocker arm nut until play in push rod is eliminated, then tighten adjusting nut 3/4 additional turn. With engine at No. 1 firing position, adjust intake valves 1, 2, 5 and 7 and exhaust valves 1, 3, 4 and 8.
3. Rotate engine 360° to No. 6 firing position and follow same procedure for adjusting valves. With engine at No. 6 TDC, adjust intake valves 3, 4, 6 and 8 and exhaust valves 2, 5, 6 and 7.

TROUBLE SHOOTING

Note. To trouble shoot engine mechanical components, see appropriate TROUBLE SHOOTING article in GENERAL INFORMATION.

ENGINE

See ENGINE REMOVAL article in the ENGINE section.

Removal

1. Drain cooling system and remove air cleaner. Disconnect negative battery cable. Disconnect upper radiator hose and heater hose at manifold. Disconnect water pump by-pass hose. Disconnect PCV hose at valve cover.
2. Disconnect accelerator linkage and fuel inlet line at carburetor. Disconnect vacuum line at distributor. Remove distributor cap and mark rotor position. Remove distributor.
3. Remove air cleaner bracket, accelerator return spring bracket and accelerator bellcrank. If A/C equipped, remove compressor and bracket with lines attached. Hang compressor to side.
4. Remove upper alternator mounting bracket. Remove intake manifold bolts and pry manifold loose. Remove manifold with carburetor attached and discard all gaskets.

Installation

Clean all gasket surfaces and install gaskets on cylinder heads. Install new end seals on cylinder block. Install manifold. Tighten bolts in sequence. (Scheme 42) Install distributor. Ensure rotor is aligned with mark made during removal. Reverse removal procedure to complete installation.

Intake Manifold Tightening Sequence Tighten bolts gradually to 30 ft. lbs. (41 N.m). Scheme 42

Remove air cleaner and heat stove pipe. Remove spark plugs. Disconnect exhaust pipe from manifold. Wire exhaust pipe aside. Remove bolts. Remove manifold.

Clean surfaces. Install manifold. Tighten bolts starting at center moving to end of manifold. Connect exhaust pipe to manifold. Install spark plugs and tighten. Install air cleaner.

1. Drain cooling system. Disconnect negative battery cable. Remove intake manifold. Remove alternator and position aside. If A/C equipped, remove compressor and forward bracket. Hang compressor to side with hoses attached.
2. Remove spark plugs. Disconnect exhaust pipes at manifolds and remove manifolds. Disconnect PCV hose from valve covers. Remove valve covers. Loosen rocker arm nuts and pivot rocker arms aside.
3. Remove push rods. Mark push rods to ensure reassembly in original positions. Remove all cylinder head bolts. Loosen cylinder head from block. Remove cylinder head and gasket.

1. Reverse removal procedure to install cylinder heads. Clean gasket sealing surfaces on head and cylinder block. Ensure cylinder head bolt threads and bolt holes in block are clean.
2. If cylinder head gasket is steel type, coat both sides with sealer. Composition asbestos/steel gasket requires no sealer. Place cylinder head gasket over dowels with bead facing up. Coat cylinder head bolt threads with sealer. Tighten cylinder head bolts in sequence. (Scheme 43)
3. Install exhaust manifolds and connect exhaust pipes. Install intake manifold. Install valve train assembly. Adjust valves. See VALVE CLEARANCE ADJUSTMENT. Install remaining parts in reverse of disassembly.

Cylinder Head Tightening Sequence Tighten bolts gradually to 95 ft. lbs. (130 N.m). Scheme 43

ROCKER ARM STUDS

Push rod guides are attached to cylinder head by rocker arm studs. Replace as necessary and tighten studs.

With cylinder head removed, compress valve spring and remove valve keepers. Release spring compressor. Remove retainer, oil seal ("O" ring type), damper, spring and valve rotator.

To install valve springs, reverse removal procedure. Lubricate and install valve stem oil seal on valve stem before installing remaining components. (Scheme 44)

VALVE SPRING INSTALLED HEIGHT

Valve spring installed height is measured from top of shim or spring seat to top of valve spring or valve spring shield. Installed height should be 1.77-1.83" (44.90-46.50 mm). If installed height exceeds specifications, install shim(s) to meet specifications.

VALVE SPRING INSTALLED HEIGHT SPECIFICATIONS

Exploded View of Valve Spring Assembly. Scheme 44

VALVE GUIDE SERVICING

If valve stem-to-guide clearance is excessive, valves with oversize stems are available. Use Reamer Set (J-7049) to ream guides to correct size for oversize valve stems.

HYDRAULIC VALVE LIFTERS

1. Disassemble lifters and thoroughly clean. inspect all components for wear and damage. If any components are damaged, complete lifter assembly must be replaced.
2. If push rod seat or lifter body wear is noted, inspect the mating engine components for wear. Prior to installing, lubricate bases of lifters with Molykote.

Cutaway View of Hydraulic Valve Lifter If any parts are worn, complete lifter must be replaced. Scheme 45

1. Remove fan belts, fan and pulley. Remove alternator. Remove radiator shroud and water pump. Remove accessory drive pulley and harmonic balancer retaining bolt. Remove harmonic balancer using puller.
2. Remove cover retaining bolts and pull cover forward slightly. Using sharp knife, cut oil pan front seal flush with cylinder block. Remove cover and gasket.

1. Clean cover, oil pan, and cylinder block gasket surfaces. Cut end tabs off new oil pan front seal. Install seal in front cover, pressing seal tips in holes provided in cover. Apply 1/8" (3 mm) bead of RTV sealer to joint formed at oil pan and cylinder block.
2. Install new cover gasket and coat with sealer. Position front cover over crankshaft. Press downward against oil pan. Align cover with dowel pins and press into place. Slightly tighten 2 oil pan-to-front cover bolts. Install front cover-to-block bolts and tighten all bolts.
3. Lubricate seal contact surface on harmonic balancer. Align balancer with Woodruff key. Using Installer (J-23523), press harmonic balancer onto crankshaft. Remove installer and install bolt for balancer. Reverse removal procedure to install remaining components. Install pulleys and adjust belts.

Removal & Installation (Front Cover Removed)

Pry seal out of cover from front. Install new seal with open end of seal facing toward inside of cover. Support cover at seal area before driving in seal. Install seal.

Removal & Installation (Front Cover Installed)

With harmonic balancer removed, pry seal out of front cover. Insert seal with open end of seal facing toward engine. Install seal using Driver (J-22102) and hammer. Be careful with surface of crankshaft.

Remove front engine cover. Rotate engine until timing marks on camshaft and crankshaft sprockets are aligned. Remove bolts securing camshaft sprocket to camshaft. Remove sprocket with timing chain. Dislodge sprocket with light blow of plastic hammer.

Install timing chain on camshaft sprocket. Align timing mark on camshaft sprocket with crankshaft sprocket. (Scheme 46) Align dowel in end of camshaft with hole in camshaft sprocket. Install camshaft sprocket and bolts. Tighten sprocket bolts evenly to draw camshaft sprocket onto camshaft. Lubricate timing chain with engine oil. Install front cover.

Timing Chain Sprocket Alignment (Rotate engine until timing marks on camshaft & crankshaft gears are aligned). Scheme 46

1. Remove intake manifold, front cover, timing chain and sprockets. Remove valve covers. Loosen rocker arms until push rods and valve lifters can be removed.
2. Keep push rods and lifters in order for reassembly. Remove grille and radiator. Remove fuel pump and push rod. Thread 3 bolts into camshaft and draw camshaft out of block. Avoid damaging camshaft bearing surfaces when removing camshaft.

1. Measure camshaft bearing journals for runout. Maximum runout is .001" (.03 mm). Replace camshaft if runout is excessive. Lubricate camshaft journals with motor oil. If new camshaft is installed, coat camshaft lobes and lifters with camshaft lubricant. NOTE: New lifters, oil filter and fresh oil should be used when new camshaft is installed.
2. Position camshaft to align timing marks on sprockets. Install sprockets and timing chain. Install remaining components. Adjust hydraulic valve lifters.

CAM LOBE LIFT

1. With valve cover removed, remove rocker arm. Mount dial indicator on cylinder head. Position indicator stem on push rod with Ball Socket Adapter (J-8520). Ensure push rod is in lifter socket.
2. Rotate engine slowly until lifter is on heel of camshaft and set dial indicator to zero. Rotate engine slowly until push rod is at fully raised position. Dial indicator will give total camshaft lobe lift.

1. Camshaft and crankshaft must be removed to replace camshaft bearings. Fasten connecting rods against sides of block so there is no interference when replacing camshaft bearings. Use tape or hose to cover connecting rod bolts for protection of crankshaft journals.
2. When crankshaft and camshaft have been removed, drive camshaft rear plug from block. Index pilot of Bearing Remover (J-6098) in front camshaft bearing and install puller screw through pilot.
3. Mount remover with shoulder toward bearing. Ensure enough threads are engaged in remover. Using 2 wrenches, hold puller screw while turning nut. When bearing is free from block, remove driver and bearing from puller screw.
4. Remove remaining bearings (except front and rear) in same fashion. Pilot of remover has to be indexed in rear bearing in order to remove rear intermediate bearing. Mount remover on driver handle and remove front and rear camshaft bearings. Drive bearings toward center of block to remove.

1. Using installer mounted on driver, install front and rear bearings first by driving toward center of cylinder block. Front and rear bearings will act as guides for pilot and center remaining bearings as they are pulled into place.
2. Index pilot in front camshaft bearing and install puller screw with nut and thrust washer run to end of threads. Index new bearing in bore with oil hole of No. 1 through No. 4 bearings aligned with holes in bore of block.
3. No. 5 bearing must be positioned with oil hole at or near 6 o'clock. This is because of bore configuration for No. 5 bearing. It will be necessary to index pilot in rear bearing to install rear intermediate bearing.
4. After bearings have been installed, remove installer and ensure that oil holes are correctly aligned. Coat new rear plug with sealer and install in block. Plug depth may be flush or recessed up to depth of .031" (.80 mm).

OIL PAN

See OIL PAN REMOVAL article in the ENGINE section.

1. Drain engine oil. Remove oil pan, oil pump and cylinder heads. Rotate crankshaft until piston to be removed is at bottom of stroke. Cover piston with rag to catch any metal shavings. Remove any ridge at top of cylinder bore with ridge reamer.
2. Remove connecting rod cap nuts and rod cap. If bearings are to be reused, mark them for installation in original rod and cap. Push piston and rod assembly up and out of cylinder block. Repeat procedure to remove all piston and rod assemblies.

Note. When cleaning pistons, do not wire brush any part of piston assembly.

1. Ensure cylinder bore is clean. Use mild detergent and hot water or light honing if necessary to clean cylinder walls. Wipe bore with light engine oil and clean dry cloth. Clean crankshaft journal and bearing surface in rod.
2. Position ring gaps properly. (Scheme 47) Lubricate and install bearing inserts in rod and cap. Lightly lubricate journals, piston and cylinder bore. Compress rings with Ring Compressor (J-8037). Bearing tang slots face away from camshaft.
3. Place connecting rod and piston assembly in respective bore. Tap piston and rod assembly down. Align bearing on journal carefully to avoid damage to journal surface. Match identification marks and install rod cap. Tighten rod nuts evenly.

FITTING PISTONS

With piston and rod assemblies removed, wipe cylinder bores clean. Measure diameter of cylinder with cylinder bore gauge or inside micrometer. If cylinder is tapered more than .001" (.025 mm), honing or boring will be necessary.

FITTING RINGS

1. To check fit of rings in cylinder bore, insert ring in bore and push ring into bore .25" (6.5 mm) with head of piston. Measure ring end gap with feeler gauge.
2. Ensure ring grooves are clear of carbon and inspect grooves for nicks or burrs. Install rings with gaps staggered. All compression rings are marked on upper side. Ensure that rings move freely in grooves after installation.

Piston Ring Gap Positioning Stagger ring gaps to minimize compression loss. Scheme 47

With piston and rod assembly removed, remove piston pin using remover and installer on a press. Separate piston from connecting rod.

1. Check clearance of pin in piston. If clearance exceeds wear limit of .001" (.025 mm), piston and pin must be replaced. Position piston and rod so that valve notch in top of piston faces opposite side from bearing tang slots in connecting rod.
2. Lubricate piston pin and press in place using installer and arbor press. Do not exceed 5000 psi (352 kg/cm 2 ). Note that pin-to-rod fit is press fit. Check piston for freedom of movement on piston pin.

Piston Pin Removal and Installation Maximum piston-to-pin clearance is .0010" (.025 mm). Scheme 48

CONNECTING ROD BEARINGS

Note. Main and connecting rod bearings are precision insert type. Shims are not used for adjustment. During production, selective fitting of bearing inserts may be necessary to achieve close tolerances. Therefore, half of a standard bearing insert and half of a .0010" (.025 mm) undersize bearing insert may be found on the same journal. During repairs, always replace both inserts as a set.

1. Drain engine oil. Remove oil pan and oil pump. Remove cylinder heads and intake manifold. Match mark each cap and rod with cylinder number. Remove rod cap nuts. Remove rod cap and bearing. Push up on piston and rod assembly and remove bearing from rod.
2. Inspect bearings for wear or damage and replace as necessary. Check crankshaft rod bearing journal for out-of-round or excessive taper. If crankshaft is out-of-round or tapers more than .001" (.025 mm), crankshaft must be removed and ground for undersize bearings.
3. Check crankshaft clearance using Plastigage method. If clearance is excessive, .0010" (.025 mm) or .0020" (.051 mm) undersize bearings may be installed to correct clearance.
4. If clearance is still excessive, crankshaft must be removed and ground for undersize bearings. Connecting rod bearings are available .010" (.26 mm) and .020" (.51 mm) undersize. Crankshaft must be replaced if journals are already at maximum undersize.

Clean rod and cap surfaces where bearing seats. Install bearings in rod and cap. Ensure tangs engage properly. Tighten rod cap nuts evenly. When all rod caps are installed, lightly tap each rod parallel to crankshaft. Measure side clearances between adjacent rod caps on common journals.

MAIN BEARINGS

Note. Main and connecting rod bearings are precision insert type. Shims are not used for adjustment. During production, selective fitting of bearing inserts may be necessary to achieve close tolerances. Therefore, half of a standard bearing insert and half of a .0010" (.025 mm) undersize bearing insert may be found on the same journal. During repairs, always replace both inserts as a set.

1. Drain oil. Remove oil pan and oil pump. Main bearings may be removed and installed without removing crankshaft from engine. Remove spark plugs if changing bearings without removing crankshaft. Number and index main bearing caps to cylinder block before removing caps.
2. Use Plastigage method to measure main bearing wear. Remove main bearing caps one at a time for measurement. Accessory drive belts must be loosened when measuring No. 1 (front) main bearing. Incorrect reading could be caused by tension of belts on snout of crankshaft.
3. Remove bearing caps. Insert main bearing remover (or bent cotter pin) in crankshaft oil hole. Rotate crankshaft clockwise as viewed from front of engine. Roll upper bearing out of block.
4. Oil new upper bearing and insert plain end (without tang) between crankshaft and side of block with locating notch. Rotate bearing into place and take remover out of crankshaft oiling hole. Oil new lower bearing and install in cap.
5. Install main bearing cap with arrow pointing toward front of engine. Ensure cap is installed in same location from which it was removed. Tighten all main bearing caps except rear main bearing cap to 110 ft. lbs. (149 N.m).
6. Tighten rear main bearing cap to 10 ft. lbs. (14 N.m). Tap crankshaft rearward and then forward in bearings. This will cause rear main bearing and crankshaft thrust surfaces to line up. Now tighten all main bearing caps to 110 ft. lbs. (149 N.m).

THRUST BEARING END PLAY

Pry crankshaft forward as far as possible and check end play with feeler gauge inserted between front of rear main bearing and crankshaft. Replace rear main bearing if end play is excessive. (Scheme 49)

Checking Crankshaft End Play End play should not exceed .002-.006" (.05-.15 mm). Scheme 49

Remove rear main bearing cap. Pry out lower half of old oil seal. To remove upper half of old seal, tap one end with brass pin punch until other end of seal protrudes enough to be removed with pliers.

Scheme 50

1. Fabricate installer from shim stock. (Scheme 50) Clean any old sealant or dirt from bearing cap and crankshaft with nonabrasive cleaner. Coat seal lips and seal bead of upper seal with motor oil.
2. Keep mating ends of seal half dry of oil. Position installer tip between crankshaft and seal seat in cylinder block. Position seal between tip of installer and crankshaft with seal bead contacting tip.
3. Ensure oil sealing lip points toward front of engine. Installer must remain in position until seal is positioned with both ends flush with block. (Scheme 50): Rear Main Seal Installer Use seal installer like a "shoehorn" to help install & protect seal.
4. Roll seal around crankshaft, using installer as "shoehorn" to protect seal bead from sharp corner of seat surface in cylinder case. Ensure oil seal lip is positioned toward front of engine.
5. Remove installer, taking care not to remove seal. Install lower half of seal in bearing cap, using installer as "shoehorn" again. Feed seal into cap using light pressure with thumb and finger.
6. Install bearing cap with sealant applied to case-to-cap face. Do not allow sealant to get on split line of seal. Tighten rear main bearing cap to 10 ft. lbs. (14 N.m). Tap end of crankshaft rearward and then forward with a lead hammer to line up thrust surfaces. Tighten rear main bearing cap to 110 ft. lbs. (149 N.m).

Rear Main Oil Seal Oil seal lip faces toward front of engine. Scheme 51

1. Disconnect negative battery ground cable. Drain cooling system and remove accessory drive belts. Remove fan hub attaching bolts. Remove fan and pulley.
2. Remove bolts attaching upper and lower alternator braces to water pump and swing brace aside. Remove lower radiator hose, heater hose and by-pass hose from water pump. Remove water pump attaching bolts and water pump.

1. Transfer heater and by-pass hose fittings to new water pump. Clean all gasket mating surfaces. Apply silicone to gasket surfaces. Reverse removal procedure to complete installation.
2. Fill cooling system and start engine. Run engine with radiator cap off until thermostat opens (upper radiator hose gets hot). Top radiator up until coolant level reaches bottom of filler neck with engine idling. Install radiator cap. Ensure arrows line up with overflow tube.

Note. For further information on cooling systems, see ENGINE COOLING SYSTEM article in the ENGINE section.

CRANKCASE CAPACITY

Crankcase capacity is 6 qts. (5.7L). Add 1 qt. (.95L) with filter change.

OIL FILTER

Replace every other oil change or more often under dusty conditions.

NORMAL OIL PRESSURE

Normal oil pressure should be 40-60 psi (2.8-4.2 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

Engine oiling is provided by pressure lubrication through full-flow oil filter supplied by gear-type oil pump. Main oil gallery feeds oil through drilled passages to camshaft and crankshaft to lubricate bearings. Valve lifter gallery feeds valve lifters, which feed rocker arms through hollow push rods. Pistons and piston pins are lubricated by oil splash.

Removal & Disassembly

1. Drain oil and remove oil pan. Remove pump-to-rear main cap bolt and remove pump and extension shaft. Remove pump cover attaching screws and pump cover.
2. Remove pressure regulator from pump cover. Mark gears so they may be reassembled with same teeth indexing. Remove idler gear, drive gear, and shaft from pump body.
3. Remove pressure regulator valve retaining pin, pressure regulator valve, washer and spring. Examine pick-up screen and pipe. If screen or pipe are damaged, pump must be replaced as assembly. Screen and pipe assembly are welded to pump body.

Reassembly & Installation

Check operation of oil pump. Check all parts for fit and wear. If pump gears or body are damaged or worn, replacement of entire pump assembly is necessary. Reverse removal and disassembly procedure to assemble and install.

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 SPECS

VALVE SPRING SPECIFICATIONS

VALVE SPRINGS SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

See also:
• ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION