GM Firebird 1967-1981 Repair Guide

Piston and Connecting Rods

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REMOVAL & INSTALLATION 230 and 250 Engines



See Figures 1, 2 and 3

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Fig. Fig. 1: Position a ring in the cylinder bore using an inverted piston to ensure it is properly seated, then measure the ring end-gap with a feeler gauge



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



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

  1. Remove the rocker arm cover.
  2.  
  3. Disconnect the fuel and vacuum lines from the carburetor.
  4.  
  5. Remove the cylinder head and the intake and exhaust manifold as an assembly.
  6.  
  7. Remove the ring ridge, using an appropriate cutter.
  8.  


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.

  1. Remove the oil pan.
  2.  
  3. Mark the connecting rod and piston assembly to make sure that they go into the same cylinder and that the same piston face is pointing toward the front of the engine upon reassembly. Do not reverse the bearing caps on the end of the connecting rods.
  4.  
  5. Remove the bearing cap and carefully push the piston and rod from its bore. Do not allow the piston and rod assembly to be scratched, nicked, or struck against a hard surface.
  6.  
  7. Using a ring compressor, insert the rod and piston assembly into the cylinder.
  8.  
  9. Pull the assembly into place against the crankpin, install the bearing cap and tighten it to 33 ft. lbs.
  10.  
  11. Install the oil pan.
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  13. Install the cylinder head assembly.
  14.  
  15. Connect the fuel and vacuum lines and install the rocker arm cover.
  16.  

231, 265, 301, 305, 326, 400, 403 and 455 Engines See Figures 4, 5 and 6

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Fig. Fig. 4: Ring gap and piston/connecting rod assembly positioning for 231 V6 engines



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Fig. Fig. 5: On some Pontiac 8-cylinder engines, the dimples on the side of the connecting rod identify the thrust face side



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Fig. Fig. 6: Piston/connecting rod positioning for Pontiac 8-cylinder engines


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.

  1. Drain the crankcase and remove the oil pan. Remove the oil pump as described later in this section.
  2.  


CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Drain the cooling system and remove the cylinder heads.
  2.  
  3. Remove any ridge or deposits from the upper end of the cylinder bores with a ridge reamer. Do this with the piston in the Bottom Dead Center position and a clean rag on top of the piston to collect cuttings.
  4.  
  5. Check the rods and pistons for identification numbers and, if necessary, number them.
  6.  
  7. Remove the connecting rod cap nuts and caps. Push the rods away from the crankshaft and install the caps and nuts loosely on their respective rods.
  8.  
  9. Push the piston and rod assemblies up and out of the cylinders.
  10.  
  11. Before replacing the rings, inspect the cylinder bores. If the cylinder bore is in satisfactory condition, place each ring in its bore in turn and square it in the bore with the head of the piston. Measure the ring end-gap. If the gap is greater than the limit, get a new ring. If the gap is less than the limit, file the end of the ring to obtain the correct gap.
  12.  
  13. Check the ring side-clearance by installing the rings on the piston, and inserting a feeler gauge of the correct dimension between the ring and the lower land. The gauge should slide freely around the circumference of the ring without binding. Any wear will form a step on the lower land. Replace any pistons having high steps. Before checking the ring side-clearance be sure the ring grooves are clean and free of carbon, sludge, or grit.
  14.  
  15. Install piston rings with a ring expander. Compression rings have a mark which must face the top of the piston. The top ring is chrome or molybdenum faced. When installing oil rings, do the following: first, install the oil ring in the ring groove and insert the anti-rotation tang into the oil hole; then, holding the ends of the spacer so they butt up against one another, install the lower steel oil ring rail; repeat this procedure to install the upper rail so that the gap will line up with that of the lower rail; flex the oil ring assembly to make sure it is free if it binds, the ring groove must be dressed at a narrow point, or a distorted ring must be replaced; install the lower compression ring with the gap 120 degrees (one third of a circle) away from oil ring gap; install the top ring with its gap 120 degrees away from that of the second ring. Be sure to install the piston in its original bore. Install the piston and rod assembly with the connecting rod bearing tang slots on the side opposite the camshaft. Install short lengths of rubber tubing over the connecting rod bolts to prevent damage to the rod journals. Lubricate pistons and rod bearings with light engine oil. Install a ring compressor over the rings on the piston. Lower the piston and rod assembly into the bore until the ring compressor contacts the block. Using the wooden handle of a hammer, push the piston into the bore while guiding the rod onto the journal.
  16.  

See Figures 7 through 13

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Fig. Fig. 7: Use a ring expander tool to remove the piston rings



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Fig. Fig. 8: Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 9: You can use a piece of an old ring to clean the piston grooves, BUT be careful, the ring is sharp



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Fig. Fig. 10: Measure the piston's outer diameter using a micrometer



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Fig. Fig. 11: A telescoping gauge may be used to measure the cylinder bore diameter



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Fig. Fig. 12: A properly cross-hatched cylinder bore



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Fig. Fig. 13: Most rings are marked to show which side should face upward

 
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