Mazda Trucks 1972-1986 Repair Guide

Crankshaft and Main Bearings

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REMOVAL



  1. Remove the engine assembly as previously outlined.
  2.  
  3. Remove the engine front cover.
  4.  
  5. Remove the timing chain/belt/gears and sprockets.
  6.  
  7. Remove the oil pan.
  8.  
  9. Remove the oil pump.
  10.  
  11. Remove the flywheel.
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  13. Stamp the cylinder number on the machined surfaces of the bolt bosses of the connecting rods and caps for identification when installing. If the pistons are to be removed from the connecting rod, mark the cylinder number on each piston with an indelible marker, silver pencil or quick drying paint for proper cylinder identification and cap to rod location.
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  15. Remove the connecting rod caps and store them so that they can be installed in their original positions.
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  17. Remove all the main bearing caps.
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  19. Note the position of the keyway in the crankshaft so it can be installed in the same position.
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  21. Lift the crankshaft out of the block. The rods will pivot to the center of the engine when the crankshaft is removed.
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  23. Remove the rear main oil seal.
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INSPECTION AND INSTALLATION



See Figures 1 through 9

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Fig. Fig. 1: A dial gauge may be used to check crankshaft end-play



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Fig. Fig. 2: Carefully pry the shaft back and forth while reading the dial gauge for play



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Fig. Fig. 3: A dial gauge may also be used to check crankshaft run-out



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Fig. Fig. 4: Turn the crankshaft slowly by hand while checking the gauge



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Fig. Fig. 5: Mounting a dial gauge to read crankshaft run-out



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Fig. Fig. 6: Another method for checking crankshaft end-play is to use a feeler bladegently pry the crankshaft in one direction and insert the feeler blade between the crankshaft and the thrust bearing. Check the crankshaft specifications chart for proper end-play



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Fig. Fig. 7: Align the thrust bearing as illustrated. Torque the caps to specifications



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Fig. Fig. 8: Measure the main bearing clearance by comparing the flattened strip to the Plastigage scale as shown



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Fig. Fig. 9: Fabricate a roll-out pin as illustrated, if necessary

  1. Using a dial indicator, check the crankshaft journal runout. Measure the crankshaft journals with a micrometer to determine the correct size rod and main bearings to be used. Whenever a new or reconditioned crankshaft is installed, new connecting rod bearings and main bearings should be installed. See Main Bearings and Rod Bearings.
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  3. Clean all oil passages in the block (and crankshaft if it is being reused).
  4.  

A new rear main seal should be installed anytime the crankshaft is removed or replaced.

  1. Install sufficient oil pan bolts in the block to align with the connecting rod bolts. Use rubber bands between the bolts to position the connecting rods as required. Connecting rod position can be adjusted by increasing the tension on the rubber bands with additional turns around the pan bolts or thread protectors.
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  3. Position the upper half of main bearings in the block and lubricate them with engine oil.
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  5. Position crankshaft keyway in the same position as removed and lower it into block. The connecting rods will follow the crank pins into the correct position as the crankshaft is lowered.
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  7. Lubricate the thrust flanges with rebuilding oil. Install caps with the lower half of the bearings lubricated with engine oil. Lubricate the cap bolts with engine oil and install, but do not tighten.
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  9. With a block of wood, bump the shaft in each direction to align the thrust flanges of the main bearing. After bumping the shaft in each direction, wedge the shaft to the front and hold it while torquing the thrust bearing cap bolts.
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In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a wood or rubber mallet before the bolts are installed. Do not use attaching bolts to pull the main bearing caps into their seats. Failure to observe this information may damage the cylinder block or a bearing cap.

  1. Torque all main bearing caps to specification. Check crankshaft end-play, using a flat feeler gauge.
  2.  
  3. Remove the connecting rod bolt thread protectors and lubricate the connecting rod bearings with engine oil.
  4.  
  5. Install the connecting rod bearing caps in their original position. Torque the nuts to specification.
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  7. Complete the installation by reversing the removal steps.
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CHECKING BEARING CLEARANCE



  1. Remove the bearing cap and wipe the oil from the crankshaft journal and the outer and inner surfaces of the bearing shell.
  2.  
  3. Place a piece of plastic gauging material in the center of the bearing.
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  5. Use a floor jack or other means to hold the crankshaft against the upper bearing shell. This is necessary to obtain accurate clearance readings when using plastic gauging material.
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  7. Install the bearing cap and bearing. Place engine oil on the cap bolts and install. Torque the bolts to specification.
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  9. Remove the bearing cap and determine the bearing clearance by comparing the width of the flattened plastic gauging material at its widest point with the graduations on the gauging material container. The number within the graduation on the envelope indicates the clearance in millimeters or thousandths of an inch. If the clearance is greater than allowed, REPLACE BOTH BEARING SHELLS AS A SET. Recheck the clearance after replacing the shells. (Refer to Main Bearing Replacement).
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BEARING REPLACEMENT



Main bearing clearances must be corrected by the use of selective upper and lower shells. Undersized bearings are available in sizes of 0.25mm, 0.50mm and 0.75mm. UNDER NO CIRCUMSTANCES should the use of shims behind the shells to compensate for wear be attempted. To install the main bearing shells, proceed as follows:

  1. Remove the oil pan as outlined below. On some models, the oil pump may also have to be removed.
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  3. Loosen all main bearing caps.
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  5. Remove the bearing cap and remove the lower shell.
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  7. Insert a flattened cotter pin or roll pin in the oil passage hole in the crankshaft, then rotate the crankshaft in the direction opposite to cranking rotation. The pin will contact the upper shell and roll it out.
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  9. The main bearing journals should be checked for roughness and wear. Slight roughness may be removed with a fine grit polishing cloth saturated with engine oil. Burrs may be removed with a fine oil stone. If the journals are scored or ridged, the crankshaft must be replaced.
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The journals can be measured for out-of-round with the crankshaft installed by using a crankshaft caliper and inside micrometer or a main bearing micrometer. The upper bearing shell must be removed when measuring the crankshaft journals. Maximum out-of-round of the crankshaft journals must not exceed 0.050mm (0.00197 in.).

  1. Clean the crankshaft journals and bearing caps thoroughly for installing new main bearings.
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  3. Apply clean engine oil or rebuilding oil, to the thrust flanges of bearing shells.
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  5. Place a new upper shell on the crankshaft journal with locating tang in the correct position and rotate the shaft to turn it into place using a cotter pin or roll pin as during removal.
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  7. Place a new bearing shell in the bearing cap.
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  9. Install a new oil seal in the rear main bearing cap and block.
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  11. Lubricate the main bearings with engine oil. Lubricate the thrust surface with lubricant rebuilding oil.
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  13. Lubricate the main bearing cap bolts with engine oil.
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In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a wood or rubber mallet before the attaching bolts are installed. Do not use attaching bolts to pull the main bearing caps into their seats. Failure to observe this information may damage the cylinder block or a bearing cap.

  1. Torque the main bearing cap bolts as specified.
  2.  

 
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