4.3l v6 - Vins [n,z] GMC Value Van P2500

ENGINE IDENTIFICATION

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

Engine identification number is stamped on a machined pad on front of cylinder block, immediately forward of right cylinder head. Engine can be identified by the eighth character of the Vehicle Identification Number (VIN). The VIN is located on a metal tag on the top left corner of the instrument panel, visible through the windshield.

ENGINE IDENTIFICATION CODES

Valve Arrangement

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

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

1. Rotate engine until No. 1 piston is on TDC at end of compression stroke. With piston in this position, adjust valves listed in «VALVE CLEARANCE ADJUSTMENT»(/gmc/value-van-p2500/1985-1987/remont/mechanical/#43l-v6-vins-nz) table, using the following procedure
2. Loosen rocker arm adjusting nut until play is felt in push rod. Tighten adjusting nut until play in push rod is removed. When play has been removed, tighten adjusting nut one full turn.
3. Rotate crankshaft 360° to bring No. 4 piston on TDC at end of compression stroke. Adjust remaining valves listed in «VALVE CLEARANCE ADJUSTMENT»(/gmc/value-van-p2500/1985-1987/remont/mechanical/#43l-v6-vins-nz) table.

VALVE CLEARANCE ADJUSTMENT

ENGINE

See ENGINE REMOVAL article.

Removal

1. Disconnect negative battery cable. Remove air cleaner. Drain cooling system. On van models, remove engine cover. On all models, remove air injection crossover hose.
2. Remove heater and radiator hoses. Remove alternator upper bracket. Label and disconnect necessary wires and hoses. Disconnect fuel line at carburetor. Disconnect carburetor linkage.
3. Remove spark plug wires. Remove distributor cap and mark position of rotor with chalk. Remove distributor. If equipped, remove A/C compressor and bracket. Remove brake vacuum pipe. Remove carburetor. Remove manifold bolts and intake manifold.

Scheme 1

1. Clean all gasket mating surfaces. Apply 3/16" bead of silicone sealer at front and rear intake manifold mounting surface of cylinder block. Extend bead of sealer 1/2" up each cylinder head. (Scheme 1) (Scheme 1): Silicone Sealer Application Points. Install intake manifold before sealer sets up (10-15 minutes).
2. Install intake manifold gaskets on cylinder heads. Install manifold and tighten attaching bolts. (Scheme 2) Install distributor with rotor pointing to chalk mark. To complete installation, reverse removal procedure.

Intake Manifold Tightening Sequence. Scheme 2

Remove heat stove tube. Remove spark plug heat shields. Disconnect oxygen sensor wire (left manifold). Disconnect exhaust pipe from manifold and wire aside. Remove bolts, then exhaust manifolds.

Note. If installing a new right side manifold, carburetor heat stove must be transferred from old unit.

Installation

Clean all gasket mating surfaces. Install manifold and tighten attaching bolts. To complete installation, reverse removal procedure. Start engine and check for leaks.

1. Drain cooling system, including block. Remove intake and exhaust manifolds. Remove A/C compressor and bracket (if equipped). Remove alternator. Remove valve covers.
2. Loosen rocker arm nuts and rotate rocker arms to side. Remove push rods in sequence for reinstallation in original locations. Remove cylinder heads.

1. Clean all gasket surfaces. Use gasket sealer on steel head gaskets. Do not use sealer on steel/asbestos head gaskets. Position gaskets on cylinder block and install heads.
2. Coat threads of head bolts with sealing compound. Install and tighten head bolts. (Scheme 3) To complete installation, reverse removal procedure. Lubricate valve tip, rocker arm pivot and push rod socket with Molykote prior to installation. Adjust valves.

Cylinder Head Tightening Sequence. Tighten cylinder head bolts to 65 ft. lbs. (90 N.m). Scheme 3

ROCKER ARM STUDS

Rocker arm studs that are loose in head or have damaged threads can be replaced with oversize studs. Use Reamer (J-5715) for .003" (.08 mm) oversize replacement studs, and Reamer (J-6036) for .013" (.33 mm) oversize replacement studs.

Remove stud using Stud Remover (J-5802-1). Install remover over stud. Tighten nut on remover to extract stud from cylinder head.

Ream hole for oversize stud. Coat press-fit area of stud with hypoid axle grease. Drive stud into place with Stud Driver (J-6880). When driver bottoms out on head, stud is at correct height.

1. With rocker arm cover removed, remove spark plug, rocker arm and push rod of cylinder to be serviced. Install air hose with adapter in spark plug hole, and turn on air supply. Do not remove air supply until all components are reinstalled.
2. Using valve spring compressor, compress valve spring and remove retainer locks. Release spring compressor and remove retainer, cap (intake), rotator (exhaust), shield, spring, damper and oil seal. (Scheme 4)

Valve Spring Assembly. Rotators are used on exhaust valves. Scheme 4

Install damper, spring, shield, cap (intake), rotator (exhaust) and retainer. Using spring compressor, compress valve spring, and install new oil seal and retainer locks. Remove spring compressor. Remove air hose and adapter. Install remaining components in reverse order of removal.

VALVE SPRING INSTALLED HEIGHT

Measure installed height from spring seat (or top of shim), to top of spring shield. Installed height should be 1.69-1.75" (42.92-44.45 mm). If installed height exceeds specifications, shim to meet specifications. Installed height should never be more than specified height.

VALVE GUIDE SERVICING

If valve stem-to-guide clearance is excessive, valves with oversize stems are available. Replacement valves are available with .003" (.08 mm), .015" (.38 mm) and .030" (.76 mm) oversize stems. Exhaust valves are available in standard size only. Always use reamers in proper size sequence.

HYDRAULIC VALVE LIFTERS

1. Disassemble lifters and thoroughly clean. Inspect all components for wear and damage. If any components are worn or damaged, complete lifter assembly must be replaced.
2. If push rod seat or lifter body wear is noted, inspect mating engine components for wear. Prior to installing, lubricate bases of lifters with Molykote. (Scheme 5)

Cutaway View of Valve Lifter Assembly. Replace lifters as complete assemblies; do not interchange parts between lifters. Scheme 5

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. Remove all mounting brackets and coolant hoses attached to water pump. Remove water pump, front cover and gasket.

1. Clean all gasket mating surfaces. Remove any excess oil pan gasket material extending beyond cylinder block.
2. Coat front cover gasket with gasket sealer and position on cover. Install cover-to-pan seal. Position cover on cylinder block. Loosely install cover-to-block upper attaching bolts. Tighten bolts alternately and evenly while pressing downward on cover, to allow dowels in block to enter holes in cover.
3. Install remaining cover bolts. Tighten all front cover bolts. Reverse removal procedure to install remaining components.

Removal (Front Cover Installed)

Remove vibration damper. Pry seal out of cover with screwdriver, using care not to damage cover seal surface.

Install new seal with open end toward inside of cover. Drive seal into place using Seal Driver (J-23042).

Removal (Front Cover Removed)

Pry seal out of cover with screwdriver, using care not to damage cover seal surface.

Install new seal with open end of seal toward inside of cover. Support cover at seal recess area. Using seal installer, drive seal into position.

Remove 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 a gear puller to remove sprocket.

Use a hammer and hollow driver to install crankshaft sprocket onto crankshaft. Install camshaft sprocket and timing chain. Ensure timing marks on sprockets are aligned. Install and tighten sprocket bolts. (Scheme 6)

Aligning Timing Sprocket Marks. Tighten camshaft sprocket bolts to 18 ft. lbs. (24 N.m). Scheme 6

Remove intake manifold, engine front cover and timing chain. Remove valve covers. Loosen all rocker arm nuts and rotate rockers to one side. Remove push rods and lifters in sequence, for reinstallation in original locations. Remove radiator and grille. Remove fuel pump and push rod. Remove camshaft.

1. Coat camshaft lobes with Molykote, and journals with engine oil. Install camshaft. Temporarily place camshaft sprocket on camshaft and align timing marks. Install camshaft sprocket and chain. Tighten camshaft sprocket attaching bolts.
2. Lubricate timing chain with engine oil. When a new camshaft is installed, always install new lifters, and change oil and replace filter. Install remaining components. Adjust valves.

CAM LOBE LIFT

1. With valve cover removed, remove rocker arm assemblies. Mount dial indicator on rocker arm stud. 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. Zero dial indicator. Rotate engine until push rod is fully raised. Record lobe lift reading and compare with specifications. If not within limits, replace camshaft and lifters.

Remove engine from vehicle. Remove oil pan, oil pump, crankshaft and camshaft. Push pistons to top of cylinder bores. Remove rear bore plug. Using camshaft bearing remover/installer, remove camshaft bearings.

Bearings are installed using bearing remover/installer. 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. Coat camshaft rear bore plug with sealer, and install flush to 1/32" (.79 mm) deep.

OIL PAN

See OIL PAN REMOVAL article.

1. Remove oil pan, oil pump and cylinder heads. Position piston at bottom of stroke and cover with cloth to collect metal cuttings. Remove any ridge from top of cylinder bore with a ridge reamer.
2. If necessary, mark connecting rod and cap for cylinder identification. Remove connecting rod cap, and cover rod bolts with rubber hose. Push piston and rod assembly out top of cylinder bore.

Scheme 7

1. Before installing piston and rod assembly, ensure ring gaps are properly spaced. (Scheme 7) Lightly coat pistons, rings and cylinder walls with engine oil. Install rod bearings in rod and cap, and lubricate with engine oil. (Scheme 7): Desired Ring Gap Spacing
2. Compress piston rings with ring compressor. Do not allow ring position to change. Cover rod bolts with rubber hose. Install piston and rod assembly into cylinder bore, with bearing tang slots facing away from camshaft. Install and tighten rod cap.

FITTING PISTONS

1. Using telescopic gauge and micrometer, measure cylinder bore diameter at a point 2 1/2" from top of bore. Measure piston diameter across piston skirt, at centerline of piston pin. Difference between two measurements is piston-to-cylinder bore clearance.
2. Using cylinder bore gauge, measure cylinder bore taper by working gauge up and down in bore. Taper must not exceed .001" (.03 mm). To determine out-of-round, take measurements at different points in bore, by rotating bore gauge horizontally, around entire circumference of bore. Out-of-round must not exceed .002" (.05 mm).
3. If taper or out-of-round are not within limits, hone or bore cylinders for installation of new pistons.

FITTING RINGS

1. Position ring 1/4" from top of cylinder bore. Ring must be square in bore. Measure ring end gap with a feeler gauge. Check side clearance of compression rings prior to installing.
2. Check ring for binding in ring groove. To check for binding, insert outer edge of ring in its respective groove, and slide ring around entire circumference of piston groove. If binding occurs, check piston groove for high steps, or check ring for distortion.

Using an arbor press and piston pin remover/installer, press piston pin from piston and connecting rod.

Check clearance of piston pin in piston. Replace piston and pin if not within limits. Lubricate piston pin holes in piston and connecting rod with engine oil. Using pin remover/installer and arbor press, press piston pin into piston and connecting rod. Check piston for freedom of movement on piston pin.

CONNECTING ROD BEARINGS

Note. Following procedures are performed with oil pan and oil pump removed. Remove oil film from surfaces to be checked.

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. Check rod bearing clearance using the Plastigage method. If clearance exceeds specifications, undersize bearings may be used in combination to produce correct clearance. If clearance is still excessive, crankshaft must be reconditioned.
4. 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. Install and tighten rod cap.

CRANKSHAFT MAIN BEARINGS

Note. Some production crankshafts are ground to .009" (.23 mm) undersize at the assembly plant. They are identified as follows: crankshaft counterweight of undersize journal, will be stamped on one side with the number "9", along with a large spot of Light Green paint. Main bearing cap will be painted Light Green on each side.

Note. Following procedures are performed with oil pan and oil pump removed. Remove oil film from surfaces to be checked.

1. Measure main bearing clearances one at a time, while all other main caps are properly tightened. Mark or identify main bearing cap before removing. Support crankshaft weight, using a jack placed under counterweight next to the bearing being checked.
2. Start with rear main bearing (No. 5) and work forward. Also, remove drive belts from crankshaft pulley, prior to checking front (No. 1) bearing. Check main bearing clearance using Plastigage method. Install cap and tighten to specifications. Do not allow crankshaft to turn.
3. Remove cap and measure width of Plastigage with scale furnished. Undersize bearing halves may be used in combination to obtain correct clearance. Always replace both upper and lower bearing halves.
4. Upper main bearings are removed from cylinder block using Upper Main Bearing Remover/Installer (J-8080). Insert remover/installer in crankshaft oil hole and rotate crankshaft clockwise. If remover/installer is not available, a cotter pin may be bent, as necessary, to do the job.
5. Lubricate journal and bearings. Insert plain end of new bearing between crankshaft and notched side of block. Insert bearing remover/installer into crankshaft oil hole, and rotate bearing into place.
6. Install lower bearing half into cap. Install and tighten main bearing caps with arrows pointing toward front of engine. Check crankshaft end play after aligning thrust bearing. Check end play by prying crankshaft forward, and inserting feeler gauge between crankshaft counterweight and forward face of rear main bearing cap.

CRANKSHAFT END PLAY

1. Ensure all other main bearing caps have been properly tightened. Tighten rear main bearing cap to 10-12 ft. lbs. (14-16 N.m). Tap crankshaft rearward, then forward, using a lead hammer. Tighten rear main bearing cap. Retighten all main bearing caps.
2. Measure crankshaft end play with a feeler gauge. Pry crankshaft forward and measure clearance between front of rear main bearing and crankshaft thrust surface.

Remove transmission, clutch (if equipped) and flywheel. Install screw driver in notches located on rear seal retainer. (Scheme 8) Pry seal from retainer. Note direction of seal lip.

Scheme 8

1. Ensure all surfaces are clean. Lubricate inner and outer seal area with engine oil. Place seal on Seal Installer (J-35621). Place seal installer against crankshaft.
2. Thread attaching screws in crankshaft. Tighten screws to square seal with crankshaft. Rotate handle until it bottoms. Remove seal installer and components. Install flywheel, clutch and transmission.

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. Apply 1/8" bead silicone sealer to water pump gasket surfaces. Using new gaskets, install and tighten water pump. 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 4 qts. (3.8L). Add one qt. (.95L) when replacing oil filter.

OIL FILTER

Replace oil filter at every other oil change, or more often under dusty or severe conditions.

NORMAL OIL PRESSURE

With engine at normal operating temperature, oil pressure should be 30-35 psi (2.1-2.5 kg/cm 2 ).

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, 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. Timing chain and sprockets are lubricated by oil drainage from No. 1 camshaft bearing. (Scheme 9)

Engine Oiling System. Scheme 9

Remove oil pan. Remove pump-to-rear main bearing cap bolt, and remove pump 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. Be sure to mark gears at a meshing point, prior to disassembly of pump. (Scheme 10)

Oil Pump Assembly. Scheme 10

Inspection

1. Wash all parts and dry with compressed air. Inspect pump body and cover for cracks or excessive wear. Inspect pump gears for damage or excessive wear. If pump gears or body are damaged or worn, replace entire pump assembly.
2. Check drive gear shaft for looseness in pump body. Inspect oil inlet tube and screen assembly for damage. Check pressure regulator valve for fit in bore.

Reassembly

If removed, install oil inlet tube and screen assembly. Apply sealer to end of tube, and tap tube into place, using plastic hammer. Install pump gears into pump body, with marked gear teeth indexing. Idler gear must be installed with smooth side of gear toward cover opening. Reassemble remaining components in reverse order of disassembly.

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 and tighten attaching bolt. Install oil pan.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

GENERAL ENGINE SPECIFICATIONS

GENERAL SPECIFICATIONS (VIN N)

GENERAL SPECIFICATIONS (VIN Z)

VALVE SPECIFICATIONS

VALVE SPECIFICATIONS

PISTON/PIN/RING SPECIFICATIONS

PISTONS, PINS & RINGS SPECIFICATIONS

BEARING SPECIFICATIONS

CRANKSHAFT MAIN & CONNECTING ROD BEARING SPECIFICATIONS

VALVE SPRING SPECIFICATIONS

VALVE SPRINGS SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

CAMSHAFT SPECIFICATIONS

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