Acura Coupes and Sedans 1986-1993 Repair Guide

Pistons and Connecting Rods

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REMOVAL



See Figures 1, 2 and 3

Although the pistons and connecting rods can be removed from the engine (after the cylinder head and oil pan are removed) while the engine is still in the car; it is far easier to work on the engine when removed from the car, and advisable for assembly cleanliness.

  1. Remove the engine from the vehicle and mount it on a suitable workstand.
  2.  
  3. Remove the cylinder head(s) and the oil pan.
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  5. 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.
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  7. 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 them where they meet that also correspond with their cylinder number. Refer to the firing order diagrams in Engine Electrical to see how the cylinders are numbered. If you cannot see any identifying numbers, use a number punch set and stamp in the numbers yourself.
  8.  
  9. Rotate the crankshaft until the piston to be removed is at the bottom of the cylinder. Check for a ridge at the top of the cylinder bore before removing the piston and connecting rod assembly, referring to the Ridge Removal and Honing procedure.
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  11. Loosen the connecting rod nuts until the nuts are flush with the ends of the rod 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 insert.
  12.  
  13. Slip a piece of snug fitting rubber hose over each rod bolt, to prevent the bolt threads from damaging the crankshaft during removal.
  14.  
  15. Using a hammer handle or piece of wood or plastic, tap 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.
  16.  



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Fig. Fig. 1: Removing a ridge from the cylinder block using a ridge reamer



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Fig. Fig. 2: The proper way to remove the piston is by pushing it to the top of the bore and then removing it



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Fig. Fig. 3: Remove the piston from the block by using a hammer handle to push it out

CLEANING AND INSPECTION



See Figures 4, 5, 6 and 7

  1. Remove the piston rings using a piston ring expander. Refer to the Piston Ring Replacement procedure.
  2.  
  3. 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 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.
  4.  
  5. After cleaning, inspect the piston for scuffing, scoring, cracks, pitting or excessive ring groove wear. Replace any piston that is obviously worn.
  6.  
  7. If the piston appears okay, measure the piston diameter using a micrometer. Measure the piston diameter in the thrust direction. On all engines, measure 0.0709 in. (18mm) from the bottom of the skirt.
  8.  
  9. 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 (perpendicular to the piston pin), about 2 1 / 2 in. (63.5mm) below the cylinder block deck.
  10.  
  11. 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. Consult an automotive machine shop. If the pistons are replaced, the piston rings must also be replaced.
  12.  
  13. If the piston-to-bore clearance is okay, check the ring groove clearance. Insert the ring that will be used in the ring groove and check the clearance with a feeler gauge. Compare your measurement with specification. Replace the piston if the ring groove clearance is not within specification.
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  15. 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.
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  17. 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.
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  19. Abnormal connecting rod bearing wear can be caused by either a bent connecting rod, an improperly machined journal, or a tapered connecting rod bore.
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  21. 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.
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  23. If a connecting rod problem is suspected, consult an automotive machine shop to have the rod checked.
  24.  



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Fig. Fig. 4: Checking the cylinder bore diameter



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Fig. Fig. 5: Checking the piston diameter



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Fig. Fig. 6: Checking the piston-to-bore clearance



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Fig. Fig. 7: Checking the ring clearance using a feeler gauge

RIDGE REMOVAL AND HONING



See Figure 8

  1. Before the piston is removed from the cylinder, check for a ridge at the top of the cylinder bore. This ridge occurs because the piston ring does not travel all the way to the top of the bore, thereby leaving an unused portion of cylinder bore.
  2.  
  3. Clean away any carbon buildup at the top of the cylinder with sand paper, in order to see the extent of the ridge more clearly. If the ridge is slight, it will be safe to remove the pistons without damaging the rings or piston ring lands. If the ridge is severe, and easily catches your fingernail, it will have to be removed using a ridge reamer.
  4.  

A severe ridge is an indication of excessive bore wear. Before removing the piston, check the cylinder bore diameter with a bore gauge, as explained in the piston and connecting rod cleaning and inspection procedure. Compare your measurement with specification. If the bore is excessively worn, the cylinder will have to bored oversize and the piston and rings replaced.

  1. Install the ridge removal tool in the top of the cylinder bore. Carefully follow the manufacturers instructions for operation. Only remove the amount of material necessary to remove the ridge.
  2.  


WARNING
Be very careful if you are unfamiliar with operating a ridge reamer. It is very easy to remove more cylinder bore material than you want, possibly requiring a cylinder overbore and piston replacement that may not have been necessary.

  1. After the piston and connecting rod assembly have been removed, check the clearances as explained in the piston and connecting rod cleaning and inspection procedure, to determine whether boring and honing or just light honing are required. If boring is necessary, consult an automotive machine shop. If light honing is all that is necessary, proceed to Step 5.
  2.  
  3. Honing is best done with the crankshaft removed, to prevent damage to the crankshaft and to make post-honing cleaning easier, as the honing process will scatter metal particles. However, if you do not want to remove the crankshaft, 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.  
  5. 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 your 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.
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  7. Regardless of which type of hone you use, carefully follow the manufacturers instructions for operation.
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  9. The hone should be moved up and down the bore at sufficient speed to obtain a uniform finish. A rigid hone will provide a definite cross-hatch finish; operate the rigid hone at a speed to obtain a 45-65° included angle in the cross-hatch. The finish marks should be clean but not sharp, free from embedded particles and torn or folded metal.
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  11. Periodically during the honing procedure, thoroughly clean the cylinder bore and check the piston-to-bore clearance with the piston for that cylinder.
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  13. 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.
  14.  
  15. After the bores are cleaned, wipe them down with a clean cloth coated with light engine oil, to keep them from rusting.
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Fig. Fig. 8: Honing the cylinder bore to remove any fine scratches or wear marks

PISTON PIN REPLACEMENT



All Acura engines utilize pressed-in wrist pins, which can only be removed with a press and special fixtures. Attempting to remove the wrist pins with other than these special fixtures can result in damage to the piston and/or connecting rod. If a wrist pin problem is suspected (too tight, too loose, etc.) consult an automotive machine shop.

PISTON RING REPLACEMENT



See Figures 9, 10 and 11

  1. Remove the piston rings from the piston using a piston ring expander.
  2.  
  3. Clean the piston ring grooves, check the piston-to-cylinder bore clearance and check the ring groove clearance as explained in the piston and connecting rod cleaning and inspection procedure.
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  5. 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.
  6.  
  7. 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).
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  9. 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.
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  11. 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. There is a high risk of breaking or distorting the compression rings if they are installed by hand.
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  13. Install the oil ring spacer in the bottom ring groove. Make sure the ends butt together and do not overlap. The ends must be on a solid portion of the piston, not over a drain hole.
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  15. Start the end of an oil ring rail ring into the oil ring groove above the spacer. The end gap must be approximately 1 in. (25.4mm) away from the spacer ends. 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 must be approximately 1 in. (25.4mm) on the other side of the spacer ends.
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  17. Install the lower compression ring in the piston ring expander with the proper side up. The piston ring packaging should contain instructions as to the directions the ring sides should face. Spread the ring with the expander and install it on the piston.
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  19. Repeat Step 9 to install the top compression ring. Space the compression ring gaps approximately 2 in. (50.8mm) on opposite sides of the oil ring gaps.
  20.  

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

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Fig. Fig. 9: Identifying the rings by the chamfered edge



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Fig. Fig. 10: Ring identification and general arrangement



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Fig. Fig. 11: Exact ring positioning on the piston

ROD BEARING REPLACEMENT



See Figures 12, 13 and 14

  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. Consult an automotive machine shop.
  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. 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.
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  3. Remove the bearing cap with the shell. The flattened Plastigage® will either be sticking to the bearing shell or the crankshaft journal.
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  5. 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 hundreths of a millimeter.
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  7. Compare your findings 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.
  8.  

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 are 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. For final bearing shell installation, 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.
  4.  

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

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Fig. Fig. 12: Checking rod bearing clearance using Plastigage®



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Fig. Fig. 13: Connecting rod bearing identification and selection-Vigor



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Fig. Fig. 14: Connecting rod bearing identification and selection-2.5L (V6), 2.7L and 3.2L engines

INSTALLATION



See Figures 15, 16 and 17

  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.
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  5. Coat the cylinder bore with light engine oil.
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  7. Make sure the rod bearing shells are correctly installed. 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.
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  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, or the letter F appears somewhere on the piston to indicate "front", meaning this side should face the front of the engine.
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  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.
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  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.
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  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.
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  19. 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 from the rod bolts.
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  21. Install the rod bearing cap. Lightly oil the connecting rod bolt threads and install the rod nuts. Torque to specification.
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  23. 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.
  24.  
  25. 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.
  26.  
  27. Install the oil pump, oil pan and cylinder head(s).
  28.  
  29. Install the engine in the vehicle.
  30.  



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Fig. Fig. 15: Installing the piston into the block



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Fig. Fig. 16: Piston must be installed in the proper position



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Fig. Fig. 17: Using a ring compressor to ease piston installation

 
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