GM Prizm/Nova 1985-1993 Repair Guide

Camshaft and Bearings

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REMOVAL & INSTALLATION



Camshaft end play (throughst clearance) must be checked before the cam is removed. Please refer to the Inspection section for details of this check.

1985-88 VIN Code 4 Engine

See Figures 1, 2 and 3

  1. Remove the valve cover.
  2.  
  3. Drain the cooling system.
  4.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Loosen the water pump pulley bolts.
  2.  
  3. Remove the alternator belt.
  4.  
  5. Raise the vehicle and safely support it on jackstands.
  6.  
  7. Remove the power steering pivot bolt, if so equipped.
  8.  
  9. Remove the bolt which goes through both the upper and lower timing belt covers.
  10.  
  11. Lower the vehicle to the ground. Remove the power steering pump belt if so equipped.
  12.  
  13. Remove the water pump pulley.
  14.  
  15. Disconnect the upper radiator hose at the engine water outlet.
  16.  
  17. Label and disconnect vacuum hoses.
  18.  
  19. Remove the upper timing belt cover and its gasket.
  20.  
  21. At the distributor, label and disconnect the spark plug wires, the vacuum hoses and the electrical connections. Remove the distributor.
  22.  
  23. Disconnect the hoses at the fuel pump and remove the fuel pump.
  24.  
  25. Remove the distributor gear bolt.
  26.  
  27. Remove the rocker arm assembly.
  28.  
  29. Rotate the crankshaft clockwise and set the engine to TDC/compression on No. 1 cylinder. Make sure the rockers for cylinder No. 1 are loose. If not, rotate the crankshaft 1 full turn.
  30.  
  31. Matchmark and remove the timing belt from the camshaft pulley. Support the belt so that it doesn't change position on the crankshaft pulley.
  32.  
  33. Loosen the camshaft bearing cap bolts a little at a time and in the correct sequence. After removal, label each cap.
  34.  



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Fig. Fig. 1: Loosen and remove the bearing caps in this order - 1985-88 VIN Code 4 engine

  1. Remove the camshaft oil seal (at the pulley end) and then remove the camshaft by lifting it straight out of its bearings.
  2.  


WARNING
Although reasonable in weight, the cam is brittle in nature. Handle it gently and do not allow it to fall or hit objects. It may break into pieces.

To install:
  1. When reinstalling, coat all the bearing journals with engine oil and place the camshaft in the cylinder head.
  2.  
  3. Place bearing caps Nos. 2, 3 and 4 on each journal with the arrows pointing towards the front of the engine.
  4.  
  5. Apply multi-purpose grease to the inside of the oil seal. and apply liquid sealer on the outer circumference of the oil seal.
  6.  
  7. Install the seal in position, being very careful to get it straight. Do not allow the seal to cock or move out of place during installation.
  8.  
  9. Install the bearing cap for bearing No. 1 and apply silicone sealant to the lower ends of the of the seal.
  10.  



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Fig. Fig. 2: Apply sealant to these points before reinstalling the Nova valve cover - 1985-88 VIN Code 4 engine

  1. Tighten each bearing cap little at a time and in the correct sequence. Tighten the bolts to 9 ft. lbs.
  2.  



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Fig. Fig. 3: Tighten the bearing caps in this order - 1985-88 VIN Code 4 engine

  1. Hold the camshaft with an adjustable wrench and tighten the drive gear to 22 ft. lbs.
  2.  
  3. Install the timing belt as previously outlined.
  4.  
  5. Install the rocker arm assembly.
  6.  
  7. Install the fuel pump with a new gasket and connect the hoses.
  8.  
  9. Replace the distributor and connect its vacuum hoses, electrical connections and the spark plug wires.
  10.  
  11. Install the upper timing belt cover but don't install the bolt which holds both the upper and the lower covers yet.
  12.  
  13. Connect the vacuum hoses.
  14.  
  15. Connect the upper radiator hose to the water outlet.
  16.  
  17. Install the water pump pulley and tighten the bolts finger tight.
  18.  
  19. Install the power steering drive belt if so equipped.
  20.  
  21. Elevate the vehicle and safely support it on jackstands.
  22.  
  23. Install the bolt which connects the upper and lower timing belt covers.
  24.  
  25. Install the power steering pump pivot bolt and the belt; adjust the belt tension.
  26.  
  27. Lower the vehicle. Install the alternator belt and adjust it to the correct tension.
  28.  
  29. Tighten the water pump pulley bolts.
  30.  
  31. Refill the cooling system.
  32.  
  33. Install the valve cover with a new gasket.
  34.  

1988 VIN Code 5, 1990 VIN Code 5 and 1991-92 VIN Code 6 Engines

See Figures 4, 5, 6 and 7

  1. Remove the valve covers and the timing belt cover following procedures outlined previously in this section.
  2.  
  3. Make certain the engine is set to TDC/compression on No. 1 cylinder. Remove the timing belt following procedures outlined earlier in this section.
  4.  
  5. Remove the crankshaft pulley if so desired.
  6.  
  7. Remove the camshaft timing belt pulleys.
  8.  
  9. Loosen and remove the camshaft bearing caps in the proper sequence. It it recommended that the bolts be loosened in 2 or 3 passes.
  10.  



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Fig. Fig. 4: Remove the camshaft bearing caps in this order - 1988 VIN Code 5 engine

  1. With the bearing caps removed, the camshaft(s) may be lifted clear of the head. If both cams are to be removed, label them clearly - they are not interchangeable.
  2.  


WARNING
Although reasonable in weight, the cam is brittle in nature. Handle it gently and do not allow it to fall or hit objects. It may break into pieces.

To install:
  1. When reinstalling, place the camshaft(s) in position on the head. The exhaust cam has the distributor drive gear on it. Observe the markings on the bearing caps and place them according to their numbered positions. The arrow should point to the front of the engine.
  2.  



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Fig. Fig. 5: Examples of markings on camshaft bearing caps. Note that the bearing on the right is for position No. 1 only - 1988 VIN Code 5 engine



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Fig. Fig. 6: Tighten the bearing caps (intake and exhaust) in this order - 1988 VIN Code 5 engine

  1. Tighten the bearing cap bolts in the correct sequence and in 3 passes to a final tightness of 115 inch lbs. (13 Nm)
  2.  
  3. Position the camshafts so that the guide pins (knock pins) are in the proper position. This step is critical to the correct valve timing of the engine.
  4.  



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Fig. Fig. 7: Correct position of guide pins - 1988 VIN Code 5 engine

  1. Install the camshaft timing pulleys and tighten the bolts to 34 ft. lbs. (47 Nm). Double check the positioning of the camshaft pulleys and the guide pin.
  2.  
  3. Double check the positioning of the camshaft pulleys and the guide pin.
  4.  
  5. Install the crankshaft pulley if it was removed. Tighten its bolt to 101 ft. lbs. and double check its position to be on TDC.
  6.  
  7. Install the timing belt and tensioner. Adjust the belt according to procedures outlined previously in this section.
  8.  
  9. Install the timing belt covers.
  10.  
  11. Install the valve covers.
  12.  

1989-90 VIN Code 6 Engine 1991-92 VIN Code 5 Engine 1993 VIN Code 6 & 8 Engines

See Figures 8 through 14

  1. Remove the valve cover.
  2.  
  3. Remove the timing belt covers.
  4.  
  5. Remove the timing belt and idler pulley following procedures outlined previously in this section.
  6.  
  7. Hold the exhaust camshaft with an adjustable wrench and remove the camshaft timing belt gear. Be careful not to damage the head or the camshaft during this work.
  8.  
  9. Gently turn the camshafts with an adjustable wrench until the service bolt hole in the intake camshaft end gear is straight up or in the 12 o'clock position.
  10.  



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Fig. Fig. 8: Correct position of the service bolt hole before removal of the intake camshaft - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines



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Fig. Fig. 9: Alternately loosen the bolts for the No. 1 bearing cap on both the intake and exhaust camshafts - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines

  1. Alternately loosen the bearing cap bolts in the number 1 (closest to the pulleys) intake and exhaust bearing caps.
  2.  
  3. Attach the intake camshaft end gear to the sub gear with a service bolt. The service bolt should match the following specifications:

    Thread diameter: 6.0mm
     
    Thread pitch: 1.0mm
     
    Bolt length: 16-20mm
     

  4.  



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Fig. Fig. 10: Always install a service bolt to lock the intake cam gears together - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines

  1. Uniformly loosen each intake camshaft bearing cap bolt a little at a time and in the correct sequence.
  2.  



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Fig. Fig. 11: Remove the camshaft bearing caps in this order. Intake cam shown, exhaust cam uses identical order - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines


WARNING
The camshaft must be held level while it is being removed. If the camshaft is not kept level, the portion of the cylinder head receiving the throughst may crack or become damaged. This in turn could cause the camshaft to bind or break.Before removing the intake camshaft, make sure the rotational force has been removed from the sub gear; that is, the gear should be in a neutral or unloaded state.

  1. Remove the bearing caps and remove the intake camshaft.
  2.  

If the camshaft cannot be removed straight and level, retighten the No. 3 bearing cap. Alternately loosen the bolts on the bearing cap a little at a time while pulling upwards on the camshaft gear. DO NOT attempt to pry or force the cam loose with tools.

  1. With the intake camshaft removed, turn the exhaust camshaft approximately 105°, so that the guide pin in the end is just past the 5 o'clock position. This puts equal loadings on the camshaft, allowing easier and safer removal.
  2.  



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Fig. Fig. 12: Setting the exhaust cam guide pin to the just past 5'O'clock position - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines

  1. Loosen the exhaust camshaft bearing cap bolts a little at a time and in the correct sequence.
  2.  
  3. Remove the bearing caps and remove the exhaust camshaft.
  4.  

If the camshaft cannot be removed straight and level, retighten the No. 3 bearing cap. Alternately loosen the bolts on the bearing cap a little at a time while pulling upwards on the camshaft gear. DO NOT attempt to pry or force the cam loose with tools.

To install:
  1. When reinstalling, remember that the camshafts must be handled carefully and kept straight and level to avoid damage.
  2.  
  3. Place the exhaust camshaft on the cylinder head so that the cam lobes press evenly on the lifters for cylinders Nos. 1 and 3. This will put the guide pin in the just past 5 o'clock position.
  4.  
  5. Place the bearing caps in position according to the number cast into the cap. The arrow should point towards the pulley end of the motor.
  6.  



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Fig. Fig. 13: Examples of bearing cap markings and position. Exhaust cam shown - 1989-90 VIN Code 6 engine, 1990 VIN Code 5 engine, 1991-92 VIN Code 5 engine and all 1993 engines



Click image to see an enlarged view

Fig. Fig. 14: Tighten the camshaft bearing cap bolts in this order. Exhaust cam shown, intake uses identical order - 1989-90 VIN Code 6 engine, 1991-92 VIN Code 5 engine and all 1993 engines

  1. Tighten the bearing cap bolts gradually and in the proper sequence to 9.5 ft. lbs. (115 inch lbs.)
  2.  
  3. Apply multi-purpose grease, such as GM 1051344 or similar, to a new exhaust camshaft oil seal.
  4.  
  5. Install the exhaust camshaft oil seal using tool J 35403 or similar. Be very careful not to install the seal on a slant or allow it to tilt during installation.
  6.  
  7. Turn the exhaust cam until the cam lobes of No.4 cylinder press down on their lifters.
  8.  
  9. Hold the intake camshaft next to the exhaust camshaft and engage the gears by matching the alignment marks on each gear.
  10.  
  11. Keeping the gears engaged, roll the intake camshaft down and into its bearing journals. This is tricky, but not hard to do. Take your time and pay close attention.
  12.  
  13. Place the bearing caps for Nos. 2, 3, 4 and 5 in position. Observe the numbers on each cap and make certain the arrows point to the pulley end of the motor.
  14.  
  15. Gradually tighten each bearing cap bolt in the same order as the exhaust camshaft bolts. Tighten each bolt to 9.5 ft. lbs. (115 inch lbs.)
  16.  
  17. Remove any retaining pins or bolts in the intake camshaft gears.
  18.  
  19. Install the number 1 bearing cap for the intake camshaft.
  20.  

If the No. 1 bearing cap does not fit properly, gently push the cam gear towards the rear of the engine by levering between the gear and the head.

  1. Turn the exhaust camshaft 1 full revolution from TDC/compression on No.1 cylinder to the same position. Check that the mark on the exhaust camshaft gear matches exactly with the mark on the intake camshaft gear.
  2.  
  3. Counterhold the exhaust camshaft and install the timing belt pulley. Tighten the bolt to 43 ft. lbs.
  4.  
  5. Double check both the crankshaft and camshaft positions, insuring that they are both set to TDC/compression for No. 1 cylinder.
  6.  
  7. Install the timing belt following procedures outlined previously in this section.
  8.  
  9. Install the timing belt covers and the valve cover.
  10.  

INSPECTION AND MEASUREMENT



See Figures 15, 16, 17 and 18

The end-play or throughst clearance of the camshaft(s) must be measured with the camshaft installed in the head. It may be checked before removal or after reinstallation. To check the end-play, mount a dial indicator accurate to ten one-thousandths (4 decimal places) on the end of the block, so that the tip bears on the end of the camshaft. (The timing belt must be removed. On some motors, it will be necessary to remove the pulleys for unobstructed access to the camshaft.) Set the scale on the dial indicator to zero. Using a screwdriver or similar tool, gently lever the camshaft fore-and-aft in its mounts. Record the amount of deflection shown on the gauge and compare this number to the Camshaft Specifications Chart at the beginning of this section.



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Fig. Fig. 15: Checking camshaft end play. GM tool number shown

Excessive end-play may indicate either a worn camshaft or a worn head; the worn cam is most likely and much cheaper to replace. Chances are good that if the cam is worn in this dimension (axial), substantial wear will show up in other measurements.

Mount the cam in V-blocks and set the dial indicator up on the round center journal. Zero the dial and rotate the camshaft. The circular runout should not exceed 0.06mm on the 1985-88 VIN Code 4 engine or 0.04mm on all others. Excess runout means the cam must be replaced.



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Fig. Fig. 16: Use a dial indicator to check the run-out (eccentricity of the center camshaft bearing

Using a micrometer or Vernier caliper, measure the diameter of all the journals and the height of all the lobes. Record the readings and compare them to the Camshaft Specifications Chart in the beginning of this section. Any measurement beyond the stated limits indicates wear and the camshaft must be replaced.



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Fig. Fig. 17: Use a micrometer to check the camshaft journal diameter



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Fig. Fig. 18: Measure the height of each camshaft lobe. Wear may be caused by infrequent oil changes

Lobe wear is generally accompanied by scoring or visible metal damage on the lobes. Overhead camshaft engines are very sensitive to proper lubrication with clean, fresh oil. A worn cam may be your report card for poor maintenance intervals and late oil changes.

If a new cam is required on the 1985-88 VIN Code 4 engine, order new rockers to accompany it so that there are 2 new surfaces in contact. On the twin-cam motors, a new cam will require readjusting the valves, so new shims are in order. If, by coincidence, one valve measures out the same as before, replace the present shim with a new one to get 2 new surfaces in contact.

The clearance between the camshaft and its journals (bearings) must also be measured. Clean the camshaft, the journals and the bearing caps of any remaining oil and place the camshaft in position on the head. Lay a piece of compressible gauging material (Plastigage® or similar) on top of each journal on the cam.

Install the bearing caps in their correct order with the arrows pointing towards the front (pulley end) of the motor. Install the bearing cap bolts and tighten them in 3 passes to the correct tightness of 9 ft. lbs.


WARNING
Do not turn the camshaft with the gauging material installed.

Remove the bearing caps (in the correct order) and measure the gauging material at its widest point by comparing it to the scale provided with the package. Compare these measurements to the Camshaft Specifications Chart at the beginning of this section. Any measurement beyond specifications indicates wear. If you have already measured the cam (or replaced it) and determined it to be usable, excess bearing clearance indicates the need for a new head due to wear of the journals.

Remove the camshaft from the head and remove all traces of the gauging material. Check carefully for any small pieces clinging to contact faces.

 
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