Mazda Trucks 1972-1986 Repair Guide

Timing Chain and Tensioner

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The correct installation and adjustment of the camshaft drive chain 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.

REMOVAL & INSTALLATION 1,586cc and 1,796cc Engines



See Figure 1

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Fig. Fig. 1: View of the tensioner retainer plate being inserted into a fully compressed timing chain tensioner, to ease installation on the 1,586cc and 1,796cc engines

  1. Remove the cylinder head and front cover. It is not necessary that the intake and exhaust manifolds be removed from the head.
  2.  
  3. Remove the oil pump and chain.
  4.  
  5. Remove the timing chain tensioner.
  6.  
  7. Loosen the timing chain guide strip screws.
  8.  
  9. Remove the oil slinger.
  10.  
  11. Remove the oil pump gear and chain as an assembly.
  12.  
  13. Remove the timing chain, crankshaft gear and camshaft gears from the engine.
  14.  

To install:
  1. Position the crankshaft gear in the timing chain.
  2.  
  3. Position the oil pump chain and gear on the crankshaft and oil pump. Check the oil pump drive chain slack. It should be 4mm (0.1575 in.). Adjusting the shims (between the oil pump body and cylinder block) are available in thickness of 0.15mm (0.0059 in.).
  4.  
  5. Install the oil slinger.
  6.  
  7. Install the oil pump washer and nut. Bend the washer over the nut.
  8.  
  9. Install the timing chain tensioner. Fully compress the snubber spring and wedge a screwdriver into the tensioner release mechanism. Without removing the screwdriver, install the tensioner.
  10.  
  11. Install the cylinder head and camshaft. Be sure that the valve timing is as illustrated. It must be exact. You may have to move the cam gear one or two teeth to obtain the correct alignment.
  12.  
  13. Install the rocker arm shafts and cam bearing caps.
  14.  
  15. Install and torque the cylinder head bolts.
  16.  
  17. Adjust the timing chain tension. Press in on the chain guide strip. Tighten the guide strip attaching screws. Remove the screwdriver from the tensioner, allowing the snubber to take up the chain slack.
  18.  
  19. Replace the front cover.
  20.  
  21. Adjust the valve clearance cold.
  22.  

1,970cc Engine See Figures 2, 3 and 4

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Fig. Fig. 2: View of the timing chain tension adjusting guide for the 1,970cc engine



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Fig. Fig. 3: Checking timing chain stretch on the 1,970cc engineon 1,586cc and 1,796cc engines, the measurement between the arrows should be less than 0.315 inches (8mm)



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Fig. Fig. 4: Timing chain installation on the 1,970cc engine (note that the illustration shows a view of the engine with the cylinder head down)

Chain adjuster guide, 49 3953 260, is necessary for this procedure.

  1. Remove the cylinder head and front cover. It is not necessary that the intake and exhaust manifolds be removed from the head.
  2.  
  3. Remove the oil pan, oil pump and pump drive chain.
  4.  
  5. Install the chain adjuster guide mentioned above.
  6.  
  7. Loosen the chain guide strip adjusting screws. Slightly rotate the timing chain in the direction of normal engine rotation. Press the top of the chain guide strip with a prybar and tighten the guide strip adjusting screws. Check the protrusion of the chain adjuster head, as shown. If protrusion exceeds 17mm (0.66929 in.), replace the chain.
  8.  
  9. Remove the timing chain tensioner.
  10.  
  11. Remove the timing chain from the gears.
  12.  
  13. When installing the chain, make sure that the gears and chains are aligned as shown. The alignment marks on the gears must appear on the left, and fall between the nickel plated links.
  14.  
  15. Check the slack in the oil pump drive chain, after installation. Press on the chain, midway between the gears. If slack exceeds 4.0mm (0.1575 in.), install adjusting shims between the block and oil pump body. Shims are available in thicknesses of 0.15mm (0.0059 in.). Tighten the oil pump sprocket bolt to 25 ft. lbs.
  16.  
  17. Follow step 4, above, and adjust the timing chain. Remove the guide tool.
  18.  
  19. Install the oil pan, using a new gasket and sealer.
  20.  
  21. Install all other parts in reverse order of removal.
  22.  

 
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