GM Full-Size Trucks 1988-1998 Repair Information

Camshaft

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REMOVAL & INSTALLATION



4.3L, 5.0L and 5.7L Engines

See Figures 1, 2, 3, 4 and 5


CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the coolant and remove the radiator.
  4.  
  5. If the vehicle is equipped with a mechanical fuel pump remove it.
  6.  
  7. Remove the drive belt(s).
  8.  
  9. If necessary, loosen the alternator bolts and move the alternator to one side.
  10.  



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Fig. Fig. 1: Camshaft and timing chain-4.3L engines



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Fig. Fig. 2: Camshaft and related parts-5.0L, 5.7L, 6.2L, 6.5L and 7.4L engines



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Fig. Fig. 3: Crankshaft position sensor reluctor ring location-4.3L, 5.0L, 5.7L engines



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Fig. Fig. 4: Removing the camshaft



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Fig. Fig. 5: Camshaft oil gallery plugs at the rear of the block

  1. Remove the valve covers.
  2.  
  3. Mark the lifters, pushrods, and rocker arms as to location so that they may be installed in the same position. Remove these parts.
  4.  
  5. If applicable, remove the air intake duct.
  6.  
  7. If necessary, remove the power steering pump from its brackets and move it out of the way.
  8.  
  9. If necessary, remove the air conditioning compressor from its brackets and move the compressor out of the way without disconnecting the lines.
  10.  
  11. Disconnect the hoses from the water pump.
  12.  
  13. Disengage and tag any electrical or vacuum connections that would interfere with camshaft removal.
  14.  
  15. Mark the distributor as to location in the block. Remove the distributor.
  16.  
  17. If necessary, disconnect the hood release cable at the latch.
  18.  
  19. Rmove the water pump.
  20.  
  21. Remove the front cover.
  22.  


CAUTION
Please refer to Routine Maintenance before discharging the compressor or disconnecting air conditioning lines. Damage to the air conditioning system or personal injury could result. Consult your local laws concerning refrigerant discharge and recycling. In many areas it may be illegal for anyone but a certified technician to service the A/C system. Always use an approved recovery station when discharging the air conditioning.

  1. If necessary, if the truck is equipped with air conditioning, discharge the air conditioning system and remove the condenser.
  2.  
  3. On carbureted engines remove the fuel pump eccentric, camshaft gear, oil slinger, and timing chain.
  4.  
  5. On 5.0L and 5.7L engines, remove the front engine mount through-bolts, place a piece of wood on a hydraulic jack, position the jack with the wood under the engine and raise the engine.
  6.  
  7. Remove the camshaft thrust plate (on front of camshaft) on the 4.3L.
  8.  
  9. Install 2 or 3 5 / 16 -18 bolts, 4-5 in. (101-127mm) long, into the threaded holes in the end of the shaft. Carefully remove the camshaft from the engine.
  10.  
  11. Inspect the camshaft for signs of excessive wear or damage.
  12.  

To install:
  1. Liberally coat camshaft and bearing with heavy engine oil, engine assembly lubricant or engine oil supplement, and carefully insert the cam into the engine.
  2.  
  3. On 5.0L and 5.7L engines, lower the engine and install the front mount through-bolts.
  4.  
  5. Align the timing marks on the camshaft and crankshaft gears. (refer to timing chain removal and installation).
  6.  
  7. Install the distributor using the locating marks made during removal. If any problems are encountered, refer to distributor removal and installation.
  8.  
  9. Install the camshaft thrust plate (on front of camshaft) on the 4.3L. Tighten the bolts to 105 inch lbs. (12 Nm).
  10.  
  11. Install the timing chain assembly and camshaft gear, and if applicable, the fuel pump eccentric.
  12.  
  13. Install the condenser. If the truck is equipped with air conditioning, charge the air conditioning system.
  14.  
  15. Install the lifters, pushrods, and rocker arms.
  16.  
  17. Install the front cover.
  18.  
  19. Install the water pump.
  20.  
  21. Install the torsional damper and pulley.
  22.  
  23. If removed, install the hood release cable.
  24.  
  25. Connect all electrical wiring.
  26.  
  27. Connect all vacuum connections.
  28.  
  29. Connect the hoses at the water pump.
  30.  
  31. Install the air conditioning compressor.
  32.  
  33. Install the power steering pump.
  34.  
  35. Install the alternator and drive belt(s).
  36.  
  37. Install the intake manifold.
  38.  
  39. Install the air cleaner.
  40.  
  41. Install the fuel pump, if removed.
  42.  
  43. Install the radiator.
  44.  
  45. Connect the battery.
  46.  
  47. Fill the crankcase.
  48.  
  49. Fill the cooling system.
  50.  

4.8L Engines

See Figures 6 and 7

  1. Remove the grille. Remove the radiator hoses and remove the radiator.
  2.  
  3. Remove the hydraulic lifters.
  4.  
  5. Remove the timing gear cover.
  6.  
  7. Remove the fuel pump.
  8.  
  9. Remove the distributor.
  10.  
  11. Align the timing marks on the camshaft and crankshaft gears.
  12.  
  13. Remove the camshaft thrust plate bolts.
  14.  
  15. Support and carefully remove the camshaft.
  16.  
  17. If either the camshaft or the camshaft gear is being renewed, the gear must be pressed off the camshaft. The replacement parts must be assembled in the same way. When placing the gear on the camshaft, press the gear onto the shaft until it bottoms against the gear spacer ring. The end clearance of the thrust plate should be 0.003-0.008 in. -0.031mm)
  18.  

To install:
  1. Pre-lube the camshaft lobes with clean engine oil or engine oil supplement, and then install the camshaft assembly in the engine. Be careful not to damage the bearings.
  2.  
  3. Turn the crankshaft and the camshaft gears so that the timing marks align. Push the camshaft into position and install and tighten the thrust plate bolts to 80 inch lbs. (9 Nm).
  4.  



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Fig. Fig. 6: Camshaft and related parts-4.8L engines



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Fig. Fig. 7: Removing the camshaft thrust plate bolts

  1. Check camshaft and crankshaft gear run-out with a dial indicator. Camshaft gear run-out should not exceed 0.004 in. (0.012mm) and crankshaft gear run-out should not be above 0.003 in. (0.011mm).
  2.  
  3. Using a dial indicator, check the backlash at several points between the camshaft and crankshaft gear teeth. Backlash should be 0.004-0.006 inches. (0.015-0.023mm).
  4.  
  5. Install the timing gear cover.
  6.  
  7. Install the distributor.
  8.  
  9. Install the fuel pump.
  10.  
  11. Install the valve lifters and the pushrods.
  12.  
  13. Install the radiator and fill with coolant.
  14.  

7.4L Engines

See Figure 8

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Remove the grille.
  6.  
  7. Remove the air conditioning compressor from its brackets and move the compressor out of the way without disconnecting the lines.
  8.  
  9. Drain the cooling system.
  10.  
  11. Remove the fan shroud and radiator.
  12.  
  13. Remove the drive belt(s), loosen the alternator bolts and move the alternator to one side.
  14.  



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Fig. Fig. 8: Crankshaft position sensor reluctor ring location-7.4L engines

  1. Remove the cylinder head covers.
  2.  
  3. Disconnect the hoses from the water pump.
  4.  
  5. Remove the water pump.
  6.  
  7. Remove the torsional damper and pulley.
  8.  
  9. Remove the front cover.
  10.  
  11. Mark the distributor as to location in the block. Remove the distributor.
  12.  
  13. Remove the intake manifold.
  14.  
  15. Mark the lifters, pushrods, and rocker arms as to location so that they may be installed in the same position. Remove these parts.
  16.  
  17. Rotate the camshaft so that the timing marks align.
  18.  
  19. Remove the camshaft sprocket bolts.
  20.  
  21. Pull the camshaft sprocket and timing chain off. The sprocket is a tight fit, so you'll have to tap it loose with a plastic mallet.
  22.  
  23. If equipped, unfasten the camshaft retainer bolts and remove the retainer.
  24.  
  25. Install two 5 / 16 in.-18 bolts in the holes in the front of the camshaft and carefully pull the camshaft from the block.
  26.  

To install:
  1. Liberally coat camshaft and bearing with heavy engine oil or engine assembly lubricant and insert the cam into the engine.
  2.  
  3. If equipped, install the camshaft retainer and bolts. Tighten the bolts to 10 ft lbs. (14 Nm).
  4.  
  5. Install the distributor using the locating marks made during removal. (If any problems are encountered, refer to distributor removal and installation)
  6.  
  7. Install the camshaft sprocket bolts and tighten them to 20 ft. lbs. (27 Nm) on 1988-95 models and 25 ft. lbs. (34 Nm) on 1996-98 models.
  8.  
  9. Install the lifters, pushrods, and rocker.
  10.  
  11. Install the intake manifold.
  12.  
  13. Install the front cover.
  14.  
  15. Install the torsional damper and pulley.
  16.  
  17. Install the water pump.
  18.  
  19. Connect the hoses at the water pump.
  20.  
  21. Install the cylinder head covers.
  22.  
  23. Install the alternator and drive belt(s).
  24.  
  25. Install the fan shroud and radiator.
  26.  
  27. Fill the cooling system.
  28.  
  29. Install the air conditioning compressor.
  30.  
  31. Install the grille.
  32.  
  33. Install the air cleaner.
  34.  
  35. Connect the battery.
  36.  

6.2L and 6.5L Diesel Engines


CAUTION
Please refer to Routine Maintenance before discharging the compressor or disconnecting air conditioning lines. Damage to the air conditioning system or personal injury could result. Consult your local laws concerning refrigerant discharge and recycling. In many areas it may be illegal for anyone but a certified technician to service the A/C system. Always use an approved recovery station when discharging the air conditioning.

  1. Disconnect the negative battery cable.
  2.  
  3. If the truck is equipped with A/C, have the A/C system evacuated by a qualified technician using approved equipment.
  4.  
  5. Drain the cooling system.
  6.  
  7. Remove the radiator and condenser.
  8.  
  9. Remove the grille and the parking lamp assemblies.
  10.  
  11. Remove the hood latch and brace assembly.
  12.  
  13. If necessary, remove the power steering pump, alternator and air conditioning compressor and set them aside.
  14.  
  15. Remove the valve covers.
  16.  
  17. Mark the lifters, pushrods, and rocker arms as to location so that they may be installed in the same position. Remove these parts.
  18.  
  19. Remove the cylinder head and the oil pump drive.
  20.  
  21. Remove the timing chain.
  22.  
  23. If applicable, remove the fuel pump (lift pump).
  24.  
  25. Remove the front engine mount through-bolts, place a piece of wood on a hydraulic jack, position the jack with the wood under the engine and raise the engine.
  26.  
  27. Remove the camshaft retainer plate.
  28.  
  29. Remove the spacer, if equipped.
  30.  
  31. Remove the camshaft by carefully sliding it out of the block.
  32.  

Whenever a new camshaft is installed, GM recommends replacing all the valve lifters, as well as the oil filter. The engine oil must be changed. These measures will help ensure proper wear characteristics of the new camshaft.

To install:
  1. Coat the camshaft lobes with Molykote® or an equivalent lube. Liberally tube the camshaft journals with clean engine oil and install the camshaft carefully.
  2.  
  3. Install the camshaft retainer plate and tighten the bolts to 17 ft. lbs. (23 Nm).
  4.  
  5. Lower the engine, install the front engine mount bolts and tighten them to 70 ft. lbs. (95 Nm). Tighten the nut to 50 ft. lbs. (70 Nm).
  6.  
  7. Align the timing marks.
  8.  
  9. Install the fuel pump (lift pump), if removed.
  10.  
  11. Install the timing chain assembly.
  12.  
  13. Install the front cover.
  14.  
  15. Install the valve lifters, guide plates and clamps, and rotate the crankshaft so that the lifters are free to travel.
  16.  
  17. Install the pushrods in their original order. Install the rocker shaft assemblies, then install the cylinder head covers.
  18.  
  19. Install the oil pump drive gear and the cylinder heads.
  20.  
  21. If removed, install the power steering pump, alternator and air conditioning compressor.
  22.  
  23. Install the hood latch and brace assembly.
  24.  
  25. Install the radiator and condenser.
  26.  
  27. Install the grille and the parking lamp assemblies.
  28.  
  29. Fill the cooling system and connect the battery.
  30.  
  31. Have the A/C system charged by a qualified technician.
  32.  

INSPECTION



Run-Out

See Figure 9

Camshaft run-out should be checked when the camshaft has been removed from the engine. An accurate dial indicator is needed for this procedure; engine specialists and most machine shops have this equipment. If you have access to a dial indicator, or can take your camshaft to someone who does, measure the camshaft bearing journal run-out. If the run-out exceeds the limit replace the camshaft.



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Fig. Fig. 9: Checking camshaft run-out

Lobe Height

See Figures 10 and 11

Use a micrometer to check camshaft (lobe) height, making sure the anvil and the spindle of the micrometer are positioned directly on the heel and tip of the camshaft lobe as shown in the accompanying illustration.



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Fig. Fig. 10: Checking camshaft lobe height



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Fig. Fig. 11: Checking camshaft journal diameter

End-Play

See Figure 12

After the camshaft has been installed, end-play should be checked. The camshaft sprocket should be installed on the cam. Use a dial gauge to check the end-play, by moving the camshaft forward and backward. End-play specifications should be as noted in the Camshaft Specifications chart.



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Fig. Fig. 12: Checking camshaft end-play

 
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