GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Pistons and Connecting Rods

Print


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.

REMOVAL



See Figures 1, 2, 3 and 4

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine assembly from the vehicle and secure on a suitable workstand.
  4.  
  5. Remove the intake manifold and cylinder heads.
  6.  
  7. Remove the oil pan and oil pump.
  8.  
  9. The position of each piston, connecting rod and connecting rod cap should be noted before any are removed, so they can be reinstalled in the same location.
  10.  
  11. Check the tops of the pistons and the sides of the connecting rods for identifying marks. In some engines, the top of the piston will be numbered to correspond with the cylinder number. The connecting rod and connecting rod cap should have numbers stamped on the machined surfaces next to the rod bolts that correspond with their cylinder number.
  12.  
  13. If no numbers are visible, use a number punch set and stamp the cylinder number on the connecting rod and connecting rod cap. The 2.2L and 2.5L engines are numbered 1-4 front to rear. On the 3.0L, 3.3L, 3.8L and 4.3L diesel V6s, the right (rear) bank is numbered 2,4,6, left (front) bank 1,3,5. The 2.8L and 3.1L engine are numbered 1,3,5 on the right bank, 2,4,6 on the left bank.
  14.  
  15. Rotate the crankshaft until the piston to be removed is at the bottom of the cylinder. Examine the cylinder bore above the ring travel. If the bore is worn so that a shoulder or ridge exists at the top of the cylinder, remove the ridge with a ridge reamer to avoid damaging the rings or cracking the ring lands in the piston during removal. Before operating the ridge reamer, place a shop towel on top of the piston to catch the metal shavings.
  16.  


WARNING
Be very careful when using a ridge reamer. Only remove the cylinder bore material that is necessary to remove the ridge. If too much cylinder bore material is removed, cylinder overboring and piston replacement may be necessary.

  1. Loosen the connecting rod bolt nuts until the nuts are flush with the ends of the bolts. Using a hammer and a brass drift or piece of wood, lightly tap on the nuts/bolts until the connecting rod cap is loosened from the connecting rod. Remove the nuts, rod cap and lower bearing shell.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: Use a brass drift and hammer to loosen the cap



Click image to see an enlarged view

Fig. Fig. 2: Remove the nuts, rod cap and lower bearing shell

All caps and rods are matched pairs and must be assembled together. They must also return to their original locations. Match mark all caps to rods, for both location and direction. Installing the caps on the wrong rod or facing the wrong way will cause permanent engine damage.

  1. Slip a piece of snug fitting rubber hose over each rod bolt, to prevent the bolt threads from damaging the crankshaft during removal. Using a hammer handle or piece of wood or plastic, push the rod and piston upward in the bore until the connecting rod is clear of the crankshaft journal.
  2.  



Click image to see an enlarged view

Fig. Fig. 3: Place lengths of rubber hose over the connecting rod studs in order to protect the crankshaft and cylinders from damage



Click image to see an enlarged view

Fig. Fig. 4: Carefully tap the piston out of the bore using a wooden dowel

  1. Inspect the rod bearings for scoring, chipping or other wear.
  2.  
  3. Inspect the crankshaft rod bearing journal for wear. Measure the journal diameter in several locations around the journal and compare to specification. If the crankshaft journal is scored or has deep ridges, or its diameter is below specification, the crankshaft must be removed from the engine and reground.
  4.  
  5. If the crankshaft journal appears usable, clean it and the rod bearing shells until they are completely free of oil. Blow any oil from the oil hole in the crankshaft.
  6.  

The journal surfaces and bearing shells must be completely free of oil to get an accurate reading with Plastigage®.

  1. Pull the connecting rod back onto the crankshaft rod journal and remove the rubber hoses.
  2.  
  3. Place a strip of Plastigage® lengthwise along the bottom center of the lower bearing shell, then install the cap with the shell and torque the connecting rod nuts to specification. Do not turn the crankshaft with the Plastigage® installed in the bearing.
  4.  
  5. Remove the bearing cap with the shell. The flattened Plastigage® will either be sticking to the bearing shell or the crankshaft journal.
  6.  
  7. Using the printed scale on the Plastigage® package, measure the flattened Plastigage® at its widest point. The number on the scale that most closely corresponds to the width of the Plastigage® indicates the bearing clearance in thousandths of an inch or hundredths of a millimeter.
  8.  
  9. Compare the actual bearing clearance with the bearing clearance specification. If the bearing clearance is excessive, the bearing must be replaced or the crankshaft must be ground and the bearing replaced.
  10.  

If the crankshaft is still at standard size (has not been ground undersize), bearing shell sets of 0.001, (0.0254mm) 0.002 (0.050mm) and 0.003 in. (0.0762mm) over standard size may be available to correct excessive bearing clearance.

  1. After clearance measuring is completed, be sure to remove the Plastigage® from the crankshaft and/or bearing shell.
  2.  
  3. Again remove the connecting rod cap and install the rubber hose on the rod bolts. Push the rod and piston upward in the bore until the piston rings clear the cylinder block. Remove the piston and connecting rod assembly from the top of the cylinder bore.
  4.  

CLEANING & INSPECTION



See Figures 5, 6, 7, 8 and 9

  1. Remove the piston rings from the piston. The compression rings must be removed using a piston ring expander, to prevent breakage.
  2.  



Click image to see an enlarged view

Fig. Fig. 5: Use a ring expander tool to remove the piston rings

  1. Clean the ring grooves with a ring groove cleaner, being careful not to cut into the piston metal. Heavy carbon deposits can be cleaned from the top of the piston with a scraper or wire brush, however, do not use a wire wheel on the ring grooves or lands. Clean the oil drain holes in the ring grooves. Clean all remaining dirt, carbon and varnish from the piston with a suitable solvent and a brush; do not use a caustic solution.
  2.  



Click image to see an enlarged view

Fig. Fig. 6: Clean the piston grooves using a ring groove cleaner



Click image to see an enlarged view

Fig. Fig. 7: You can use a piece of an old ring to clean the ring grooves, BUT be careful the ring is sharp

  1. After cleaning, inspect the piston for scuffing, scoring, cracks, pitting or excessive ring groove wear. Replace any piston that is obviously worn.
  2.  
  3. If the piston appears okay, measure the piston diameter using a micrometer. Measure the piston diameter in the thrust direction, 90° to the piston pin axis, 3/4 in. below the center line of the piston pin bore.
  4.  
  5. Measure the cylinder bore diameter using a bore gauge, or with a telescope gauge and micrometer. The measurement should be made in the piston thrust direction at the top, middle and bottom of the bore.
  6.  

Piston diameter and cylinder bore measurements should be made with the parts at room temperature, 70°F (21°C).



Click image to see an enlarged view

Fig. Fig. 8: A telescoping gauge may be used to measure the cylinder bore diameter



Click image to see an enlarged view

Fig. Fig. 9: Measure the piston's outer diameter using a micrometer

  1. Subtract the piston diameter measurement made in Step 4 from the cylinder bore measurement made in Step 5. This is the piston-to-bore clearance. If the clearance is within specification, light finish honing is all that is necessary. If the clearance is excessive, the cylinder must be bored and the piston replaced. If the pistons are replaced, the piston rings must also be replaced.
  2.  
  3. If the piston-to-bore clearance is okay, check the ring groove clearance. Roll the piston ring around the ring groove in which it is to be installed and check the clearance with a feeler gauge. Compare the measurement with specification. High points in the ring groove that may cause the ring to bind may be cleaned up carefully with a points file. Replace the piston if the ring groove clearance is not within specification.
  4.  
  5. Check the connecting rod for damage or obvious wear. Check for signs of fractures and check the bearing bore for out-of-round and taper.
  6.  
  7. A shiny surface on the pin boss side of the piston usually indicates that the connecting rod is bent or the wrist pin hole is not in proper relation to the piston skirt and ring grooves.
  8.  
  9. Abnormal connecting rod bearing wear can be caused by either a bent connecting rod, an improperly machined journal, or a tapered connecting rod bore.
  10.  
  11. Twisted connecting rods will not create an easily identifiable wear pattern, but badly twisted rods will disturb the action of the entire piston, rings, and connecting rod assembly and may be the cause of excessive oil consumption.
  12.  
  13. If the piston must be removed from the connecting rod, mark the side of the connecting rod that corresponds with the side of the piston that faces the front of the engine, so the new piston will be installed facing the same direction. Most pistons have an arrow or notch on the top of the piston, indicating that this side should face the front of the engine. If the original piston is to be reinstalled, use paint or a marker to indicate the cylinder number on the piston, so it can be reinstalled on the same connecting rod.
  14.  
  15. The piston pin is a press fit in the connecting rod. If the piston and/or connecting rod must be replaced, the pin must be pressed into the connecting rod using a fixture that will not damage or distort the piston and/or connecting rod. The piston must move freely on the pin after installation.
  16.  

HONING



See Figures 10 and 11

  1. After the piston and connecting rod assembly have been removed, check the clearances as explained in the cleaning and inspection procedure, to determine whether boring and honing or just light honing are required.
  2.  
  3. Honing is best done with the crankshaft removed. This prevents damage to the crankshaft and makes post-honing cleaning easier, as the honing process will scatter metal particles. However, if the crankshaft is in the cylinder block, position the connecting rod journal for the cylinder being honed as far away from the bottom of the cylinder bore as possible, and wrap a shop cloth around the journal.
  4.  



Click image to see an enlarged view

Fig. Fig. 10: Removing cylinder glazing using a flexible hone

  1. Honing can be done either with a flexible glaze breaker type hone or with a rigid hone that has honing stones and guide shoes. The flexible hone removes the least amount of metal, and is especially recommended if the piston-to-cylinder bore clearance is on the loose side. The flexible hone is useful to provide a finish on which the new piston rings will seat. A rigid hone will remove more material than the flexible hone and requires more operator skill.
  2.  



Click image to see an enlarged view

Fig. Fig. 11: A properly cross-hatched cylinder bore

  1. Regardless of the type of hone used, carefully follow the manufacturers instructions for operation.
  2.  
  3. The hone should be moved up and down the bore at sufficient speed to obtain a uniform finish. A rigid hone will provide a more definite cross-hatch finish; operate the rigid hone at a speed to obtain a 45° included angle in the cross-hatch. The finish marks should be clean but not sharp, free from embedded particles and torn or folded metal.
  4.  
  5. Periodically during the honing procedure, thoroughly clean the cylinder bore and check the piston-to-bore clearance with the piston for that cylinder.
  6.  
  7. After honing is completed, thoroughly wash the cylinder bores and the rest of the engine with hot water and detergent. Scrub the bores well with a stiff bristle brush and rinse thoroughly with hot water. Thorough cleaning is essential, for if any abrasive material is left in the cylinder bore, it will rapidly wear the new rings and the cylinder bore. If any abrasive material is left in the rest of the engine, it will be picked up by the oil and carried throughout the engine, damaging bearings and other parts.
  8.  
  9. After the bores are cleaned, wipe them down with a clean cloth coated with light engine oil, to keep them from rusting.
  10.  

PISTON PIN REPLACEMENT



Gasoline Engines

See Figure 12

Use care at all times when handling and servicing connecting rods and pistons To prevent possible damage to these units, do not clamp rod or piston is vise since they may become distorted. Do not allow pistons to strike against one another, against hard objects or bench surfaces, since distortion of piston contour or nicks in the soft aluminum material may result.

  1. Remove the piston rings using a suitable piston ring remover.
  2.  
  3. Install the guide bushing of the piston pin removing and installing tool.
  4.  
  5. Install the piston and connecting rod assembly on the support, then place the assembly in an arbor press. Press the pin out of the connecting rod, using tool J-24086-B or equivalent.
  6.  



Click image to see an enlarged view

Fig. Fig. 12: Pressing the pin out of the connecting rod

  1. Clean all disassembled parts completely.
  2.  
  3. Use a micrometer to measure the diameter of the piston pin. Use an inside micrometer to measure to piston pin bore.
  4.  

If the piston pin-to-piston clearance is in excess of 0.001 in. (0.0254mm), the piston and pin assembly must be replaced.

  1. Lubricate the piston and pin assembly and press fit together.
  2.  

Never exceed 5000 lbs. of pressure when press fitting piston and pins.

  1. After installing the piston pins, check that the piston has freedom of motion.
  2.  

Diesel Engines

The piston pin is free floating. The pin bore in the piston is 0.0003-0.0005 in. (0.0076-0.0127mm) and 0.003-0.0013 in. (0.0076-0.033mm) in the rod. If the pin-to-piston clearance is to the high limit (0.005 in./0.0127mm piston or 0.0013 in./0.033mm rod), the pin can be inserted in the piston or rod with very little hand pressure and will fall through the piston or rod by its own weight. If the clearance is okay, the pin will not fall through. It is important that the piston and rod pin hole be clean and free of oil when checking pin fit.

The rod may be installed in the piston with either side facing up. Whenever the replacement of a piston pin is necessary, remove the snapring retaining the pin. Then remove pin.

It is very important that after installing the piston pin retaining snaprings that the rings be rotated to make sure they are fully seated in their grooves. The snapring must be installed with the flat side out.

PISTON RING REPLACEMENT



  1. After the cylinder bores have been finish honed and cleaned, check the piston ring end-gap. Compress the piston rings to be used in the cylinder, one at a time, into that cylinder. Using an inverted piston, push the ring down into the cylinder bore area where normal ring wear is not encountered.
  2.  
  3. Measure the ring end-gap with a feeler gauge and compare to specification. A gap that is too tight is more harmful than one that is too loose (If ring end-gap is excessively loose, the cylinder bore is probably worn beyond specification).
  4.  
  5. If the ring end-gap is too tight, carefully remove the ring and file the ends squarely with a fine file to obtain the proper clearance.
  6.  
  7. Install the rings on the piston, lowest ring first. The lowest (oil) ring is installed by hand; the top 2 (compression) rings must be installed using a piston ring expander tool. There is a high risk of breaking or distorting the compression rings if they are installed by hand.
  8.  
  9. Install the oil ring expander in the bottom ring groove. Make sure the ends butt together and do not overlap. The expander end-gap should be parallel to the piston pin, facing the right cylinder bank.
  10.  
  11. Start the end of an oil ring rail ring into the oil ring groove above the expander. The rail end-gap should be positioned 135° from the expander end-gap. Finish installing the rail ring by spiraling it the remainder of the way on. Repeat the rail installation with the other rail ring. Its gap position must be 135° from the other side of the expander end-gap, 90° from the other rail ring end-gap.
  12.  

If the instructions on the ring packaging differ from this information regarding ring gap positioning, follow the ring manufacturers instructions.

  1. Install the lower compression ring in the piston ring expander tool with the proper side up (usually the manufacturer's mark faces UP). The piston ring packaging should contain instructions as to the directions the ring sides should face. Spread the ring with the expander tool and install it on the piston. Position the end-gap 180° from the oil ring expander end-gap.
  2.  
  3. Repeat Step 7 to install the top compression ring. Position the end-gap in line with the oil ring expander end-gap. The compression ring end-gaps must not be aligned.
  4.  

ROD BEARING REPLACEMENT



If you have already removed the connecting rod and piston assemblies from the engine, follow only steps 3-7 of the following procedure.

The connecting rod bearings are designed to have a slight projection above the rod and cap faces to insure a positive contact. The bearings can be replaced without removing the rod and piston assembly from the engine.

  1. Remove the oil pan. It may be necessary to remove the oil pump to provide access to rear connecting rod bearings.
  2.  
  3. With the connecting rod journal at the bottom, stamp the cylinder number on the machined surfaces of connecting rod and cap for identification when reinstalling, then remove caps.
  4.  
  5. Inspect journals 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 by moving the stone on the journal circumference. Do not move the stone back and forth across the journal. If the journals are scored or ridged, the crankshaft must be replaced.
  6.  
  7. The connecting rod journals should be checked for out-of-round and correct size with a micrometer.
  8.  

Crankshaft rod journals will normally be standard size. If any undersized crankshafts are used, all will be 0.254mm undersize and 0.254mm will be stamped the number 4 counterweight.

If a plastic gauging material (Plastigage® or equivalent) is to be used:

  1. Clean oil from the journal bearing cap, connecting rod and outer and inner surface of the bearing inserts. Position insert so that tang is properly aligned with notch in rod and cap.
  2.  
  3. Place a piece of plastic gauging material in the center of lower bearing shell.
  4.  
  5. Remove bearing cap and determine bearing clearances by comparing the width of the flattened plastic gauging material at its widest point with the graduation on the container. The number within the graduation on the envelopes indicates the clearance in thousandths of an inch or millimeters. If this clearance is excessive, replace the bearing and recheck clearance with plastic gauging material. Lubricate bearing with engine oil before installation. Repeat Steps 2 through 7 on remaining connecting rod bearings. All rods must be connected to their journals when rotating the crankshaft to prevent engine damage.
  6.  

INSTALLATION



  1. Make sure the connecting rod and rod cap bearing saddles are clean and free of nicks or burrs. Install the bearing shells in the connecting rod, making sure the bearing shell tangs are seated in the notches.
  2.  

Be careful when handling any bearings. Hands and working area should be clean. Dirt is easily embedded in the bearing surface and the bearings are easily scratched or damaged.

  1. Make sure the cylinder bore and crankshaft journal are clean.
  2.  
  3. Position the crankshaft journal at its furthest position away from the bottom of the cylinder bore.
  4.  
  5. Coat the cylinder bore with light engine oil.
  6.  
  7. Install the rubber hoses over the connecting rod bolts to protect the crankshaft during installation.
  8.  
  9. Make sure the piston rings are properly installed and the ring end-gaps are correctly positioned. Install a piston ring compressor over the piston and rings and compress the piston rings into their grooves. Follow the ring compressor manufacturers instructions.
  10.  
  11. Place the piston and connecting rod assembly into the cylinder bore. Make sure the assembly is the correct one for that bore and that the piston and connecting rod are facing in the proper direction. Most pistons have an arrow or notch on the top of the piston, indicating that this side should face the front of the engine.
  12.  
  13. Make sure the ring compressor is seated squarely on the block deck surface. If the compressor is not seated squarely, a ring could pop out from beneath the compressor and hang up on the deck surface. As the piston is tapped into the bore, possibly breaking the ring.
  14.  
  15. Make sure that the connecting rod is not hung up on the crankshaft counterweights and is in position to come straight on to the crankshaft.
  16.  
  17. Tap the piston slowly into the bore, making sure the compressor remains squarely against the block deck. When the piston is completely in the bore, remove the ring compressor.
  18.  

If the connecting rod bearings were replaced, recheck the bearing clearance as described during the removal procedure, before proceeding further.

  1. Coat the crankshaft journal and the bearing shells with engine assembly lube or clean engine oil. Pull the connecting rod onto the crankshaft journal. After the rod is seated, remove the rubber hoses.
  2.  
  3. Install the rod bearing cap, making sure it is the correct one for the connecting rod. Lightly oil the connecting rod bolt threads and install the rod nuts, then tighten the nuts.
  4.  
  5. After each piston and connecting rod assembly is installed, turn the crankshaft over several times and check for binding. If there is a problem and the crankshaft will not turn, or turns with great difficulty, it will be easier to find the problem (rod cap on backwards, broken ring, etc.) than if all the assemblies are installed.
  6.  
  7. Check the clearance between the sides of the connecting rods and the crankshaft using a feeler gauge. Spread the rods slightly with a screwdriver to insert the gauge. If the clearance is below the minimum specification, the connecting rod will have to be removed and machined to provide adequate clearance. If the clearance is excessive, substitute an unworn rod and recheck. If the clearance is still excessive, the crankshaft must be welded and reground, or replaced.
  8.  
  9. Install the oil pump and oil pan.
  10.  
  11. Install the cylinder heads and intake manifold.
  12.  
  13. Install the engine in the vehicle.
  14.  
  15. Run the engine and check for leaks and proper engine operation.
  16.  

 
label.common.footer.alt.autozoneLogo