Mazda Trucks 1972-1986 Repair Guide

Timing Belt

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The correct installation and adjustment of the camshaft drive belt is mandatory if the engine is to run properly. The camshaft controls the opening of the engine valves through coordination of the movement of the crankshaft and camshaft. When any given piston is on the intake stroke the corresponding intake valve must open to admit air/fuel mixture into the cylinder. When the same piston is on the compression and power strokes, both valves in that cylinder must be closed. When the piston is on the exhaust stroke, the exhaust valve for that cylinder must be open. If the opening and closing of the valves is not coordinated with the movements of the pistons, the engine will run very poorly, if at all.

INSPECTION



Inspect the belt for any visible signs of damage such as missing teeth, deep cracks or scores, or loose threads along the edges of the belt. Check that there is no oil or antifreeze leaking onto the belt, as this will soften the rubber compound and cause premature failure. As as average rule of thumb, the timing belt should be replaced every 60,000 miles (96,000 km). If the belt breaks while the engine is running, or the crankshaft and/or camshaft has been turned separately after the timing belt has been removed from the engine, the valves may strike the piston heads, and cause engine damage. If replacement is necessary, follow the precedures very closely.

REMOVAL & INSTALLATION 1,998cc Engine



See Figures 1 through 21

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Fig. Fig. 1: Do not bend, twist or turn the timing belt inside out. Never allow oil, water or steam to contact the belt



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Fig. Fig. 2: Check for premature parting of the belt



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Fig. Fig. 3: Check if the teeth are cracked or damaged



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Fig. Fig. 4: Inspect the timing belt for cracks, fraying, glazing or damage of any kind



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Fig. Fig. 5: Look for noticeable cracks or wear on the belt face



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Fig. Fig. 6: You may only have damage on one side of the belt; if so, the guide could be the culprit



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Fig. Fig. 7: Foreign materials can get in between the teeth and cause damage



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Fig. Fig. 8: Damage on only one side of the timing belt may indicate a faulty guide



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Fig. Fig. 9: ALWAYS replace the timing belt at the interval specified by the manufacturer



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Fig. Fig. 10: Camshaft (left) and crankshaft (right) timing marks on the 1,998cc engine



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Fig. Fig. 11: Camshaft sprocket removal



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Fig. Fig. 12: Always mark the timing belt for forward rotation if reinstalling an old belt



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Fig. Fig. 13: Check the timing belt tensioner for smoothness of rotationit's a good idea to replace the tensioner pulley while replacing the timing belt, as it is cheap insurance against a future failure



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Fig. Fig. 14: View of the attaching bolts for the camshaft and crankshaft sprockets on the 1,998cc engine



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Fig. Fig. 15: Closeup view of aligning the crankshaft sprocket notch with the mating mark on the 1,998cc engine



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Fig. Fig. 16: Camshaft sprocket installation on the 1,998cc engine



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Fig. Fig. 17: Align all timing marks prior to belt installation



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Fig. Fig. 18: Timing belt tensioner pulley installation on the 1,998cc engine



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Fig. Fig. 19: Location of the timing belt tensioner lockbolt on the 1,998cc engine



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Fig. Fig. 20: Tightening the tensioner lockbolt with a torque wrench



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Fig. Fig. 21: Measuring timing belt deflection

Photos of the timing belt removal can be found in the Water Pump and Cylinder Head procedures, earlier in this section.

  1. Disconnect the battery ground.
  2.  
  3. Drain the cooling system.
  4.  


CAUTION
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 quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Remove the distributor.
  2.  
  3. Remove the fan shroud and fan.
  4.  
  5. Remove the alternator.
  6.  
  7. Disconnect the air injection pipes.
  8.  
  9. Remove the fan pulley, hub and bracket.
  10.  
  11. If so equipped, remove the air conditioning compressor drive belt.
  12.  
  13. If so equipped, remove the power steering pump drive belt.
  14.  
  15. Remove the crankshaft pulley and baffle plate.
  16.  
  17. Remove the upper, then the lower, belt covers.
  18.  
  19. Turn the crankshaft so that the A mark on the camshaft pulley is at the top, aligned with the notch in the front housing.
  20.  
  21. Loosen the tensioner lockbolt and remove the tensioner spring.
  22.  
  23. Mark the forward rotation of the belt with paint to avoid confusion upon installation. Remove the belt.
  24.  
  25. Replace the belt if it has been contaminated by oil or grease, or shows any sign of damage, wear, cracks or peeling.
  26.  

To install:
  1. To ease installation of the belt, remove all the spark plugs.
  2.  
  3. Make sure that the timing mark on the camshaft is aligned as described above, and that the timing mark (notch) on the crankshaft sprocket is aligned with the triangular shaped mark on the front housing.
  4.  
  5. Install the tensioner and spring, positioning the tensioner all the way to the intake manifold side and temporarily secure it there with the lockbolt.
  6.  
  7. Install the belt onto the sprockets from YOUR right side. If you are reusing the original belt, make sure you follow the directional mark previously made.
  8.  
  9. Loosen the lockbolt so that the tensioner applies tension to the belt.
  10.  
  11. Turn the crankshaft two full revolutions in the direction of normal rotation. This will apply equal tension to all points of the belt.
  12.  
  13. Make sure that the timing marks are still aligned. If not, repeat the belt installation procedure.
  14.  
  15. Tighten the tensioner lockbolt to 30-35 ft. lbs.
  16.  
  17. Measure the timing belt tension by pressing on the belt at the midpoint of the longest straight run. Belt deflection should be 11-13mm (0.433-0.510 in.). If not, repeat the belt adjustment procedure, above.
  18.  
  19. Install the lower, then the upper, belt covers. Torque the belt cover bolts to 80 in. lbs.
  20.  
  21. Install the baffle plate and crankshaft pulley.
  22.  
  23. Install the power steering pump drive belt.
  24.  
  25. Install the air conditioning compressor drive belt.
  26.  
  27. Install the hub and bracket, and fan pulley. Torque the fan bracket bolts to 40 ft. lbs.
  28.  
  29. Connect the air injection pipes.
  30.  
  31. Install the alternator.
  32.  
  33. Install the fan shroud and fan.
  34.  
  35. Install the distributor.
  36.  
  37. Fill the cooling system.
  38.  
  39. Connect the battery ground.
  40.  

When installing the drive belts on the various accessories, check the belt deflection as follows:



Alternator
 

New: 7-8mm (0.276-0.315 in.) Used: 8-9mm (0.315-0.354 in.)



Power steering pump
 

New: 9-11mm (0.354-0.433 in.) Used: 12-14mm (0.472-0.552 in.)



Air conditioning compressor
 

New: 10-12mm (0.394-0.472 in.) Used: 12-14mm (0.472-0.552 in.)

 
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