GM: Electra/Park Avenue/Ninety-Eight 1990-1993

Pistons and Connecting Rods

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Fig. Fig. 1 Measuring piston diameter



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Fig. Fig. 2 Measuring piston ring side clearance



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Fig. Fig. 3 Cylinder wall wear pattern



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Fig. Fig. 4 Measuring connecting rod side clearance



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Fig. Fig. 5 Piston pin service using a special press



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Fig. Fig. 6 On Supercharged engine, the piston pin is held by retaining rings



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Fig. Fig. 7 Piston installation using a ring compressor



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Fig. Fig. 8 Piston installation positioning



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Fig. Fig. 9 Piston ring gap locations

REMOVAL



The engine does not have to be removed to remove a piston and connecting rod assembly. The cylinder head has to be removed, as well as the oil pan in order to access the connecting rod bolts. If more than one assembly needs to be serviced though, it is easier to remove the engine from the vehicle.

  1. Remove the engine assembly from the vehicle, see `Engine' removal and installation procedures.
  2.  
  3. Remove the intake manifold and the cylinder head over the piston assembly being removed.
  4.  
  5. Drain the oil and remove the oil pan.
  6.  
  7. Remove the oil pump and sump assembly.
  8.  
  9. Stamp the cylinder number on the machine surfaces of the bolt bosses of the connecting rod and cap for identification when reinstalling. If the pistons are to be removed from the connecting rod, mark the cylinder number on the piston with a silver pencil or quick drying paint for proper cylinder identification and cap-to-rod location. All engines are numbered 1-3-5 on the left (front) bank, 2-4-6 on the right (rear) bank.
  10.  

If the pistons or connecting rods are not marked from the factory, mark each assembly by scratching the number in the part with a scribe.

  1. Examine the cylinder bore above the ring travel. If a ridge exists, remove the ridge with a ridge reamer before attempting to remove the piston and rod assembly. This tool can be purchased at your local parts distributor or rented at a tool rental.
  2.  
  3. Remove the rod bearing cap and bearing. Tap on the lower cap to dislodge it from the connecting rod.
  4.  
  5. Install a guide hose over threads of rod bolts. This is to prevent damage to bearing journal and rod bolt threads. Use two pieces of 3 / 8 inch fuel hose.
  6.  
  7. Remove the rod and piston assembly through the top of the cylinder bore by lightly tapping the connecting rod with a wooden hammer handle. Do not use any metal tools to remove the piston and connecting rod assembly.
  8.  

If the piston rings will not clear the top of the cylinder, check to see if the ridge is completely removed.

  1. Remove all other rod and piston assemblies in the same manner.
  2.  

CLEANING AND INSPECTION



Connecting Rods

Wash connecting rods in cleaning solvent and dry with compressed air. Check for twisted or bent rods and inspect for nicks or cracks. Also check the length of the rods and replace connecting rods that are damaged.

Pistons

Clean varnish from piston skirts and pins with a cleaning solvent. Do not wire brush any part of the piston. Clean the carbon out of the ring grooves with a ring groove cleaner or use a no-longer-usable ring broken in half. Make sure oil ring holes and slots are clean.

Inspect the piston for cracked ring lands, skirts or pin bosses, wavy or worn ring lands, scuffed or damaged skirts, eroded areas at the top of the piston. Replace pistons that are damaged or show signs of excessive wear. Inspect the grooves for nicks or burrs that might cause the rings to hang up.

Measure piston skirt (across center line of piston pin) and check piston clearance.

PISTON PIN REMOVAL & INSTALLATION



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

Removing the piston from the connecting rod requires the use of expensive tools that would not be practical to purchase for a one time basis (except Supercharged engine). This procedure should be performed by a qualified engine machine shop.

3.8L VIN 1 Supercharged Engine

The piston pin is held in by retaining clips on either side of the pin, requiring no special tools to remove. Remove the retaining clips and push out the piston pin. Reuse the old retainers if not damaged. Make sure the clips are fully seated before installing into cylinder block.

Non-supercharged Engines
  1. Remove the piston rings using a suitable piston right 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 a support, and place the assembly in an arbor press. Press the pin out of the connecting rod, using the appropriate piston pin tool.
  6.  
  7. When installing the new piston, apply clean engine oil to the pin and press in with a piston pin installing tool. Make sure the connecting rod moves freely without binding after pin in installed. If not, reaming the pin hole may have to be performed.
  8.  

MEASURING THE OLD PISTONS



Check used piston-to-cylinder bore clearance as follows:

  1. Measure the cylinder bore diameter with a telescope gauge.
  2.  
  3. Measure the piston diameter. When measuring the pistons for size or taper, measurements must be made with the piston pin removed.
  4.  
  5. Subtract the piston diameter from the cylinder bore diameter to determine piston-to-bore clearance.
  6.  
  7. Compare the piston-to-bore clearances obtained with those clearances recommended in the `Piston and Connecting Rod' chart in the beginning of this Section. Determine if the piston-to-bore clearance is in the acceptable range.
  8.  
  9. When measuring taper, the largest reading must be at the bottom of the skirt.
  10.  
  11. If the measurement is not within specifications, the cylinders should be bored and new oversize pistons should be installed.
  12.  

SELECTING NEW PISTONS



  1. If the used piston is not acceptable, check the service piston size and determine if a new piston can be selected. (Service pistons are available in standard high limit and standard 0.254mm (0.010 inch) oversize.
  2.  
  3. If the cylinder bore must be reconditioned, measure the new piston diameter, then hone the cylinder bore to obtain the preferred clearance.
  4.  
  5. Select a new piston and mark the piston to identify the cylinder for which it was fitted. Aftermarket piston manufacturers can supply oversized pistons at 0.030 inch, 0.040 inch, and 0.060 inch over in most cases.
  6.  
  7. After the cylinder has been reconditioned and new pistons purchased, remeasure bore and piston to ensure proper piston fit.
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CYLINDER HONING



  1. When cylinders are being honed, follow the manufacturer's recommendations for the use of the hone.
  2.  
  3. Occasionally during the honing operation, the cylinder bore should be thoroughly cleaned and the selected piston checked for correct fit.
  4.  
  5. When finish-honing a cylinder bore, the hone should be moved up and down at a sufficient speed to obtain a very find uniform surface finish in a cross-hatch pattern of approximately 45-65 degrees included angle. The finish marks should be clean but not sharp, free from imbedded particles and torn or folded metal.
  6.  
  7. Permanently mark the piston for the cylinder to which it has been fitted and proceed to hone the remaining cylinders.
  8.  

Handle pistons with care. Do not attempt to force pistons through cylinders until the cylinders have been honed to correct size. Pistons can be distorted through careless handling.

  1. Thoroughly clean the bores with hot water and detergent. Scrub well with a stiff bristle brush and rinse thoroughly with hot water. It is extremely essential that a good cleaning operation be performed. If any of the abrasive material is allowed to remain in the cylinder bores, it will apidly wear the new rings and cylinder bores. The bores should be swabbed several times and light engine oil with a clean cloth and then wiped with a clean dry cloth. Cylinders should not be cleaned with kerosene or gasoline. Clean the remainder of the cylinder block to remove the excess material spread during the honing operation.
  2.  

CHECKING CYLINDER BORE



Cylinder bore size can be measured with inside micrometers or a cylinder gauge. The most wear will occur at the top of the ring travel.

Reconditioned cylinder bores should be held to not more than 0.025mm (0.001 inch) taper.

If the cylinder bores are smooth, the cylinder walls should not be deglazed. If the cylinder walls are scored, the walls may have to be honed before installing new rings. It is important that reconditioned cylinder bores be thoroughly washed with a soap and water solution to remove all traces of abrasive material to eliminate premature wear.

 
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