Chevrolet Citation/Omega/Phoenix/Skylark 1980-1985 Repair Guide

Pistons and Connecting Rod

Print

REMOVAL





Click image to see an enlarged view

Fig. Fig. 1 Match the connecting rods to their cylinders using a number stamp



Click image to see an enlarged view

Fig. Fig. 2 Place rubber hose over the connecting rod studs to protect the crank and bores from damage



Click image to see an enlarged view

Fig. Fig. 3 Carefully tap the piston out of the bore using a wooden dowel



Click image to see an enlarged view

Fig. Fig. 4 A telescoping gauge may be used to measure the cylinder bore diameter



Click image to see an enlarged view

Fig. Fig. 5 Measure the piston's outer diameter using a micrometer

  1. Remove the engine assembly from the car, see Engine Removal and Installation, earlier in this section.
  2.  
  3. Remove the intake manifold, cylinder head or heads, as applicable.
  4.  
  5. Remove the oil pan.
  6.  
  7. Remove the oil pump assembly.
  8.  
  9. Stamp the cylinder number on the machined 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. The 4-151 engine is numbered 1-4 from front to back; the V6-173 is numbered 1-3-5 on the right bank, 2-4-6 on the left bank.
  10.  
  11. 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.
  12.  
  13. Remove the rod bearing cap and bearing.
  14.  
  15. Install a guide hose over threads of rod bolts. This is to prevent damage to bearing journal and rod bolt threads.
  16.  
  17. Remove the rod and piston assembly through the top of the cylinder bore.
  18.  
  19. Remove any other rod and piston assemblies in the same manner.
  20.  

CLEANING & 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. 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 ring grooves with a groove cleaner and 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 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 REPLACEMENT



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 in 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 piston rings using suitable piston ring remover.
  2.  
  3. Install guide bushing of piston pin removing and installing tool.
  4.  
  5. Install piston and connecting rod assembly on support and place assembly in an arbor press. Press pin out of connecting rod, using the appropriate piston pin tool.
  6.  

MEASURING THE OLD PISTONS



Check used piston to cylinder bore clearance as follows:

  1. Measure the cylinder bore diameter with a telescope gauge or a dial gauge.
  2.  
  3. Measure the piston diameter. When measuring piston for size or taper, measurement must be made with the piston pin removed.
  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. Determine if piston-to-bore clearance is in acceptable range.
  8.  
  9. When measuring taper, the largest reading must be at the bottom of the skirt.
  10.  

SELECTING NEW PISTONS



  1. If the used piston is not acceptable, check service piston sizes and determine if a new piston can be selected. Service pistons are available in standard, high limit and standard .254 mm (.010 in.) oversize.
  2.  
  3. If the cylinder bore must be reconditioned, measure the new piston diameter then hone cylinder bore to obtain preferable clearance.
  4.  
  5. Select new piston and mark piston to identify the cylinder for which it was fitted. On some cars oversize pistons may be found. These pistons will be .254 mm (.010 in.) oversize.
  6.  

CYLINDER HONING





Click image to see an enlarged view

Fig. Fig. 6 Removing cylinder glazing using a flexible hone



Click image to see an enlarged view

Fig. Fig. 7 As with a ball hone, work the hone carefully up and down the bore to achieve the desired results

  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 very fine uniform surface finish marks in a cross hatch pattern of approximately 45 to 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 rapidly wear the new rings and cylinder bores. The bores should be swabbed several times with light engine oil and 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.  



Click image to see an enlarged view

Fig. Fig. 8 A properly cross-hatched cylinder bore

CHECKING CYLINDER BORE



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

Reconditioned cylinder bores should be held to not more than .025 mm (.001 in.) out-of-round and .025 mm (.001 in.) 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.

PISTON RINGS





Click image to see an enlarged view

Fig. Fig. 9 Use a ring expander tool to remove the piston rings



Click image to see an enlarged view

Fig. Fig. 10 Clean the piston grooves using a ring groove cleaner



Click image to see an enlarged view

Fig. Fig. 11 You can use a piece of an old ring to clean the piston grooves, BUT be careful, the ring is sharp

The pistons have three rings (two compression rings and one oil ring). The oil ring consists of two rails and an expander. Pistons do not have oil drain holes behind the rings.

RING TOLERANCES



When installing new rings, ring gap and side clearance should be checked as follows:

PISTON RING & RAIL GAP





Click image to see an enlarged view

Fig. Fig. 12 Check the ring end-gap with the ring installed in the cylinder



Click image to see an enlarged view

Fig. Fig. 13 Checking the ring-to-ring groove clearance



Click image to see an enlarged view

Fig. Fig. 14 Most rings are marked to show which side should face upward

Each ring and rail gap must be measured with the ring or rail positioned squarely and at the bottom of the ring-travel area of the bore.

SIDE CLEARANCE



Each ring must be checked for side clearance in its respective piston groove by inserting a feeler gauge between the ring and its upper land. The piston grooves must be cleaned before checking ring for side clearance. See PISTON RING CLEARANCE specifications at the end of this section for ring side clearance specifications. To check oil ring side clearance, the oil rings must be installed on the piston.

RING INSTALLATION



For service ring specifications and detailed installation productions, refer to the instructions furnished with the parts package.

CONNECTING ROD BEARINGS





Click image to see an enlarged view

Fig. Fig. 15 Apply a strip of gauging material to the bearing journal, then install and torque the cap



Click image to see an enlarged view

Fig. Fig. 16 After the cap is removed again, use the scale supplied with the gauge material to check clearances



Click image to see an enlarged view

Fig. Fig. 17 Most pistons are marked to indicate positioning in the engine (usually a mark means the side facing front)



Click image to see an enlarged view

Fig. Fig. 18 Installing the piston into the block using a ring compressor and the handle of a hammer

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, as outlined in this section. 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 .254 mm undersize and .254 mm will be stamped on the number 4 counterweight.

If plastic gauging material 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 envelope 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. Install connecting rod bolt guide hose over rod bolt threads.
  2.  
  3. Apply engine oil to the rings and piston, then install the piston ring compressing tool on the piston.
  4.  
  5. Install the assembly in its respective cylinder bore.
  6.  
  7. Lubricate the crankshaft journal with engine oil and install connecting rod bearing and cap, with bearing index tang in rod and cap on same side.
  8.  

When more than one rod and piston assembly is being installed, the connecting rod cap attaching nuts should only be tightened enough to keep each rod in position until all have been installed. This will aid installation of remaining piston assemblies.

  1. Tighten the rod bolt nuts to specification.
  2.  
  3. Install all other removed parts.
  4.  
  5. Install the engine in the car, as outlined earlier in this section.
  6.  

 
label.common.footer.alt.autozoneLogo