Chrysler Full-Size Trucks 1967-1988 Repair Guide

Pistons and Connecting Rods

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REMOVAL & INSTALLATION




CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted to 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.

All Gasoline Engines

See Figures 1 through 5

On all but the 6-251, the notch on the top of each piston must face the front of the engine.



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Fig. Fig. 1: 6-225 piston and connecting rod assembly with oil squirt holes and notch location

On the 6-251, the slot in the piston should be on the side away from the valves.


CAUTION
The EPA warns that prolonged contact with used engine oil may cause a number of skin disorders, including cancer! You should make every effort to minimize your exposure to used engine oil. Protective gloves should be worn when changing the oil. Wash your hands and any other exposed skin areas as soon as possible after exposure to used engine oil. Soap and water, or waterless hand cleaner should be used.

To position the connecting rod correctly, the oil squirt hole should point to the right side on all six-cylinder engines. On all V8 engines, the larger chamfer of the lower connecting rod bore must face to the rear on the right bank and to the front on the left bank.



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Fig. Fig. 2: V8 piston and connecting rod assembly with oil squirt holes and notch location

  1. Disconnect the battery ground cable.
  2.  
  3. Drain the engine oil and cooling system.
  4.  
  5. Disconnect and remove parts for removal of the cylinder head.
  6.  
  7. Remove the cylinder head.
  8.  
  9. Remove the timing chain/gears.
  10.  
  11. Remove the oil pan.
  12.  
  13. Pistons should be removed following the firing order of the engine. Turn the crankshaft until the piston to be removed is at the bottom of its stroke.
  14.  
  15. Place a cloth on the head of the piston to be removed and, using a ridge reamer, remove the deposits from the upper end of the cylinder bore.
  16.  


WARNING
Never remove more than1/32in. (25.4mm) from the ring travel area when removing the ridges!

  1. Mark all connecting rod bearing caps so that they may be returned to their original locations in the engine. The connecting rod caps are usually marked. The marks must be matched when re-assembling the engine. Mark all pistons so they can be returned to their original cylinders.
  2.  

After removing the connecting rod cap and bearing, place a short length of rubber hose over the rod bolts to prevent cylinder wall and crank journal scoring when removing or installing the piston and rod assembly.

  1. Using an internal micrometer, measure the bores across the thrust faces of the cylinder and parallel to the axis of the crankshaft at a minimum of four equally spaced locations. The bore must not be out-of-round by more than 0.005 in. (0.12mm) and it must not taper more than 0.010 in. (0.25mm). Taper is the difference in wear between two bore measurements in any one cylinder.
  2.  
  3. If the cylinder bore is in satisfactory condition, place each ring in the bore in turn and square it in the bore with the head of the piston. Measure the ring gap. If the ring gap is greater than the limit, get a new ring. If the ring gap is less than the limit, file the end of the ring to obtain the correct gap.
  4.  
  5. Check the ring side clearance by installing rings on the piston, and inserting a feeler gauge of the correct dimension between the ring and the lower land. The gauge should slide freely around the ring circumference without binding. Any wear will form a step on the lower land. Replace any pistons having high steps. Before checking the ring side clearance, be sure that the ring grooves are clean and free of carbon, sludge, or grit.
  6.  



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Fig. Fig. 3: Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 4: You can use a piece of an old ring to clean the ring grooves, BUT be careful the ring is sharp

  1. Piston rings should be installed so that their ends are at three equal spacings. Avoid installing rings with their ends in line with the piston pin bosses and the thrust direction.
  2.  
  3. Install the pistons in their original bores, if you are reusing the same pistons. Install short lengths of rubber hose over the connecting rod bolts to prevent damage to the cylinder walls or rod journal.
  4.  



Click image to see an enlarged view

Fig. Fig. 5: Place lengths of rubber hose over the connecting rod studs in order to protect the crankshaft and cylinders from damage

  1. Install a ring compressor over the rings on the piston. Lower the piston and rod assembly into the bore until the ring compressor contacts the block. Using a wooden hammer handle, push the rod into the bore while guiding the rod onto the journal.
  2.  

Diesel Engines

See Figures 6, 7 and 8

  1. Disconnect the battery ground.
  2.  
  3. Drain the cooling system.
  4.  
  5. Remove the dipstick and tube.
  6.  
  7. Disconnect and remove the road draft tube from the oil pan.
  8.  
  9. Remove the automatic transmission cooling lines and bracket.
  10.  
  11. Remove the oil pan.
  12.  
  13. Remove the oil pick-up tube and gasket.
  14.  
  15. Turn the crankshaft until the connecting rod journal of the piston to be removed is at bottom center. Remove the connecting rod cap nuts. Install short pieces of hose on the studs to prevent journal damage. Mark the rod cap to ensure proper identification. Remove the cap and bearing inserts.
  16.  



Click image to see an enlarged view

Fig. Fig. 6: Number each rod and cap with its cylinder number for correct assembly and installation

  1. Push the connecting rod and piston assembly up and out of the way and measure the rod journal OD with a micrometer. It should be 2.281-2.282 in. (57.945-57.965mm). The crankpin repair limit is 0.006 in. (0.15mm). If the crankpin OD measures 0.035 in. (0.9mm) or more, the crankshaft must be replaced.
  2.  
  3. Remove the cylinder head.
  4.  
  5. Remove the ridge from the top of the sleeve with a ridge reamer.
  6.  
  7. Using a hardwood block, drive the piston up and out of the block.
  8.  
  9. Using an internal micrometer, measure the bores across the thrust faces of the cylinder and parallel to the axis of the crankshaft at a minimum of four equally spaced locations. The bore must not be out-of-round by more than 0.005 in. (0.12mm) and it must not taper more than 0.010 in. (0.25mm). Taper is the difference in wear between two bore measurements in any one cylinder.
  10.  
  11. If the cylinder bore is in satisfactory condition, place each ring in the bore in turn and square it in the bore with the head of the piston. Measure the ring gap. If the ring gap is greater than the limit, get a new ring. If the ring gap is less than the limit, file the end of the ring to obtain the correct gap.
  12.  



Click image to see an enlarged view

Fig. Fig. 7: Piston ring gap positioning

  1. Check the ring side clearance by installing rings on the piston, and inserting a feeler gauge of the correct dimension between the ring and the lower land. The gauge should slide freely around the ring circumference without binding. Any wear will form a step on the lower land. Replace any pistons having high steps. Before checking the ring side clearance, be sure that the ring grooves are clean and free of carbon, sludge, or grit.
  2.  
  3. Piston rings should be installed so that their ends are at three equal spacings. Avoid installing rings with their ends in line with the piston pin bosses and the thrust direction.
  4.  



Click image to see an enlarged view

Fig. Fig. 8: Piston ring installation

  1. Install the pistons in their original bores, if you are reusing the same pistons. Install short lengths of rubber hose over the connecting rod bolts to prevent damage to the cylinder walls or rod journal.
  2.  
  3. Install a ring compressor over the rings on the piston. Lower the piston and rod assembly into the bore until the ring compressor contacts the block. Using a wooden hammer handle, push the rod into the bore while guiding the rod onto the journal.
  4.  

 
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