Chevrolet Chevette/1000 1976-1988 Repair Guide

Pistons and Connecting Rods (Gasoline Engine)

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REMOVAL





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Fig. Fig. 1Place rubber hose over the connecting rod studs to protect the crank and bores from damage

  1. Remove the oil pan, oil pump and cylinder head as previously outlined.
  2.  
  3. For the cylinder being serviced, turn crankshaft until piston is at bottom of the stroke. Place a cloth on top of the piston.
  4.  
  5. Use a ridge reamer to remove any ridge and/or deposits from the upper end of the cylinder bore.
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  7. Turn the crankshaft until the piston is at top of stroke and remove cloth and cuttings.
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  9. Remove the connecting rod cap and cover the studs with plastic tubing or other similar devices. Remove assembly.
  10.  

DISASSEMBLY





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Fig. Fig. 2Remove the piston pin using a suitable arbor press



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Fig. Fig. 3Use a ring expander tool to remove the piston rings

  1. Remove connecting rod bearings from connecting rods and caps. If bearings are being reused, place them in a rack so they may be reinstalled in their original position.
  2.  
  3. Remove piston rings by expanding and sliding them off the pistons. Tool J-25220 is available for this purpose.
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  5. Place connecting rod and piston assembly on Tool J-24086-20. Using an arbor press and piston pin remover, J-24086-8, press the piston pin out of connecting rod and piston.
  6.  

The above special tools or their equivalents may be used.

CLEANING AND INSPECTION



Connecting Rods
  1. Wash connecting rods in cleaning solvent and dry with compressed air.
  2.  
  3. Check for twisted or bent rods and inspect for nicks or cracks. Replace connecting rods that are damaged.
  4.  

Pistons


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Fig. Fig. 4Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 5You can use a piece of an old ring to clean the piston grooves, BUT be careful, the ring is sharp

  1. Clean varnish from piston skirts and pins with a cleaning solvent. Clean the ring grooves with a groove cleaner and make sure oil ring holes and slots are clean.
  2.  


WARNING
Do not wire brush any part of the piston.

  1. Inspect the piston for cracked ring lands, skirts or pin bosses, wavy or worn ring lands, scuffed or damaged skirts, eroded areas at 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.
  2.  

Piston Pins

The piston pin clearance is designed to maintain adequate clearance under all engine operating conditions. Because of this, the piston and piston pin are a matched set and not serviced separately.

Inspect piston pin bores and piston pins for wear. Piston pin bores and piston pins must be free of varnish or scuffing when being measured. The piston pin should be measured with a micrometer and the piston pin bore should be measured with a dial bore gauge or an inside micrometer. If clearance is in excess of the 0.026mm wear limit, the piston and piston pin assembly should be replaced.

Piston Selection
  1. Check used piston to cylinder bore clearance as follows:
  2.  
    1. Measure the cylinder bore diameter with a telescopic gauge.
    2.  
    3. Measure the piston diameter (at skirt across centerline of piston pin).
    4.  
    5. Subtract piston diameter from cylinder bore diameter to determine piston-to-bore clearance.
    6.  
    7. Compare piston-to-bore clearance obtained with those clearances recommended in specifications section, and determine if piston-to-bore clearance is in acceptable range.
    8.  

  3. If used piston is not acceptable, check piston size and determine if a new piston can be selected to fit cylinder bore.
  4.  
  5. If cylinder bore must be reconditioned, measure new piston diameter (across centerline of piston pin) then hone cylinder bore to obtain preferable clearance.
  6.  
  7. Select new piston and mark piston to identify the cylinder for which it was fitted.
  8.  



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Fig. Fig. 6A telescoping gauge may be used to measure the cylinder bore diameter



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Fig. Fig. 7Measure the piston's outer diameter using a micrometer

ASSEMBLY





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Fig. Fig. 8Installation of the piston pin



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Fig. Fig. 9Most rings are marked to show which side should face upward



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Fig. Fig. 10Checking the ring-to-ring groove clearance

  1. Lubricate piston pin holes in piston and connecting rod to facilitate installation of pin.
  2.  
  3. Place connecting rod in piston and hold in place with piston pin guide and piston pin. Place assembly on fixture and support assembly.
  4.  
  5. Using piston pin installer, J-24086-9, press the piston pin into the piston and connecting rod.
  6.  


WARNING
After installer hub bottoms on support assembly, do not exceed 5000 psi pressure, as this could cause structural damage to the tool.

  1. Remove piston and connecting rod assembly from tool and check piston for freedom of movement on piston pin.
  2.  

Piston Rings

All compression rings are marked on the upper side of the ring. When installing compression rings, make sure the marked side is toward the top of the piston. The top ring is treated with molybdenum for maximum life.

The oil control rings are of the three piece type, consisting of two segments (rails) and a spacer.

  1. Select rings comparable in size to the piston being used.
  2.  
  3. Slip the compression ring in the cylinder bore; then press the ring down into the cylinder bore about 6mm (above ring travel). Be sure ring is square with cylinder wall.
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  5. Measure the space or gap between the ends of the ring with a feeler gauge.
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  7. If the gap between the ends of the ring is below specifications, remove the ring and try another for fit.
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  9. Fit each compression ring to the cylinder in which it is going to be used.
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  11. If the pistons have not been cleaned and inspected as outlined, do so.
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  13. Slip the outer surface of the top and second compression ring into the respective piston ring groove and roll the ring entirely around the groove to make sure that the ring is free. If binding occurs at any point the cause should be determined, and if caused by ring groove, remove by dressing with a fine cut file. If the binding is caused by a distorted ring, check a new ring.
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  15. Install piston rings as follows:
  16.  
    1. Install oil ring spacer in groove.
    2.  
    3. Hold spacer ends butted and install lower steel oil ring rail with gap properly located.
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    5. Install upper steel oil ring rail with gap properly located.
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    7. Flex the oil ring assembly to make sure the ring is free. If binding occurs at any point the cause should be determined, and if caused by ring groove, remove by dressing groove with a fine cut file. If binding is caused by a distorted ring, check a new ring.
    8.  
    9. Install second compression ring with gaps properly located.
    10.  
    11. Install top compression ring with gap properly located.
    12.  

  17. Proper clearance of the piston ring in its piston ring groove is very important to provide proper ring action and reduce wear. Therefore, when fitting new rings, the clearances between the surfaces of the ring and groove should be measured.
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INSTALLATION





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Fig. Fig. 11Most pistons are marked to indicate positioning in the engine (usually a mark means the side facing front)



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Fig. Fig. 12Installing the piston into the block using a ring compressor and the handle of a hammer

Cylinder bores must be clean before piston installation. This may be accomplished with a hot water and detergent wash. After cleaning, the bores should be swabbed several times with light engine oil and a clean dry cloth.

  1. Lubricate connecting rod bearings and install in rods and rod caps.
  2.  
  3. Lightly coat pistons, rings and cylinder walls with light engine oil.
  4.  
  5. With bearing caps removed, cover the connecting rod bolts with plastic tubing or other similar device.
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  7. Install each connecting rod and piston assembly in its respective bore. Install with notch on piston facing front of engine. Use tool J-26468 to compress the rings. Guide the connecting rod into place on the crankshaft journal. Use a hammer handle and light blows to install the piston into the bore. Hold the ring compressor firmly against the cylinder block until all piston rings have entered the cylinder bore.
  8.  
  9. Remove the plastic tubing from the connecting rod bolts.
  10.  
  11. Install the bearing caps and torque retaining nuts to specification. Be sure to install new pistons in the same cylinders for which they were fitted, and used pistons in the same cylinder from which they were removed. Each connecting rod and bearing cap should be marked, beginning at the front of the engine. The numbers on the connecting rod and bearing cap must be on the same side when installed in the cylinder bore. If a connecting rod is ever transposed from one block or cylinder to another, new bearings should be fitted and the connecting rod should be numbered to correspond with the new cylinder number.
  12.  

ROD BEARING INSPECTION AND REPLACEMENT





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Fig. Fig. 13Apply a strip of gauging material to the bearing journal, then install and torque the cap



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Fig. Fig. 14After the cap is removed again, use the scale supplied with the gauge material to check clearances

Connecting rod bearings are of the precision insert type and do not utilize shims for adjustment. If clearances are found to be excessive, a new bearing will be required. Service bearings are available in standard, 0.026mm U.S. and 0.050mm U.S. for use with new and used standard crankshafts, and in 0.250mm U.S. and 0.500mm U.S. for reconditioned crankshafts.

  1. Remove the connecting rod cap and bearing.
  2.  
  3. Inspect the bearing for evidence of wear or damage. Bearings showing the above should not be reinstalled.
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  5. Wipe both upper and lower bearing shells and crankpin clean of oil.
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  7. Measure the crankpin for out-of-round or taper with a micrometer. If not within specifications, replace or recondition the crankshaft. If within specifications and a new bearing is to be installed, measure the maximum diameter of the crankpin to determine new bearing size required.
  8.  
  9. If within specifications, measure new or used bearing clearances with Plastigage® or its equivalent. If a bearing is being fitted to an out-of-round crankpin, be sure to fit the maximum diameter of the crankpin. If the bearing is fitted to the minimum diameter and the crankpin is out-of-round 0.025mm, interference between the bearing and crankpin will result in rapid bearing failure.
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    1. Place a piece of gauging plastic the full width of the crankpin, parallel to the crankshaft.
    2.  
    3. Install the bearing in the connecting rod and cap.
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    5. Install the bearing cap and evenly torque the nuts to specifications. Do not turn the crankshaft with the gauging plastic installed.
    6.  
    7. Remove the bearing cap and using the scale on the gauging plastic envelope, measure the gauging plastic width at its widest point.
    8.  

  11. If the clearance exceeds specifications select a new, correct size bearing and remeasure the clearance. Be sure to check what size bearing is being removed in order to determine proper replacement size bearing.
  12.  

If the clearance cannot be brought to within specifications, the crankpin will have to be machined to the closest undersize. If the crankpin is already at maximum undersize, replace the crankshaft.

  1. Coat the bearing surface with oil, install the rod cap and torque the nuts to specifications.
  2.  
  3. When all connecting rod bearings have been installed, tap each rod lightly (parallel to the crankpin) to make sure they have clearance.
  4.  
  5. Measure all connecting rod side clearances (see specifications), between the connecting rod cap and side of crankpin.
  6.  

 
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