Chevrolet Full-size Cars 1968-1978 Repair Guide

Pistons and Connecting Rods

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REMOVAL & INSTALLATION





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



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Fig. Fig. 2 Carefully tap the piston out of the bore using a wooden dowel



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Fig. Fig. 3 This ridge must be removed before the pistons can be taken out of the engine



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Fig. Fig. 4 Match the connecting rods to their caps, and identify their cylinders, by using a scribe ...



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Fig. Fig. 5 ... or by using a number punch/stamp

Before removing the pistons, the top of the cylinder bore must be examined for a ridge. A ridge at the top of the bore is the result of normal cylinder wear, caused by the piston rings only traveling so far up the bore in the course of the piston stroke. The ridge can be felt by hand; it must be removed before the pistons are removed.

A ridge reamer is necessary for this operation. Place the piston at the bottom of its stroke, and cover it with a rag. Cut the ridge away with the ridge reamer, using extreme care to avoid cutting too deeply. Remove the rag, and remove the cuttings that remain on the piston with a magnet and a rag soaked in clean oil. Make sure the piston top and cylinder bore are absolutely clean before moving the piston.

  1. Remove intake manifold and cylinder heads.
  2.  
  3. Remove oil pan.
  4.  
  5. Remove oil pump assembly if necessary.
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  7. Matchmark the connecting rod cap to the connecting rod with a scribe; each cap must be reinstalled on its proper rod in the proper direction. Remove the connecting rod bearing cap and the rod bearing. Number the top of each piston with silver paint or a felt-tip pen for later assembly.
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  9. Cut lengths of 3 / 8 in. diameter hose to use as rod bolt guide. Install the hose over the threads of the rod bolts, to prevent the bolt threads from damaging the crankshaft journals and cylinder walls when the piston is removed.
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  11. Squirt some clean engine oil onto the cylinder wall from above, until the wall is coated. Carefully push the piston and rod assembly up and out of the cylinder by tapping on the bottom of the connecting rod with a wooden hammer handle.
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  13. Place the rod bearing cap back on the connecting rod, and install the nut temporarily. Using a number stamp or punch, stamp the cylinder number on the side of the connecting rod and cap; this will help keep the proper piston and rod assembly on the proper cylinder.
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On all V8s, starting at the front the right bank cylinders are 2-4-6-8 and the left bank 1-3-5-7.

  1. Remove remaining pistons in similar manner.
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On all engines, the notch on the piston will face the front of the engine for assembly. The chamfered corners of the bearing caps should face toward the front of the left bank and toward the rear of the right bank, and the boss on the connecting rod should face toward the front of the engine for the right bank and to the rear of the engine on the left.

On various engines, the piston compression rings are marked with a dimple, a letter T, a letter O, GM or the word TOP to identify the side of the ring which must face toward the top of the piston.

CLEANING & INSPECTING





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Fig. Fig. 6 Cylinder bore measuring points



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Fig. Fig. 7 Measuring the cylinder bore with a dial gauge



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Fig. Fig. 8 Use a ring expander tool to remove the piston rings



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Fig. Fig. 9 Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 10 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. 11 A telescoping gauge may be used to measure the cylinder bore diameter



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Fig. Fig. 12 Measure the piston's outer diameter using a micrometer



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Fig. Fig. 13 Removing cylinder glazing using a flexible hone



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Fig. Fig. 14 As with a ball hone, work the hone carefully up and down the bore to achieve the desired results



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Fig. Fig. 15 A solid hone can also be used to cross-hatch the cylinder bore



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Fig. Fig. 16 A properly cross-hatched cylinder bore



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Fig. Fig. 17 Most rings are marked to show which side should face upward

A piston ring expander is necessary for removing piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the ring being bent, scratched or distorted, or the piston itself being damaged. When the rings are removed, clean the ring grooves using an appropriate ring groove cleaning too, using care not to cut too deeply. Thoroughly clean all carbon and varnish from the piston with solvent.


WARNING
Do not use a wire brush or caustic solvent (acids, etc.) on piston. Inspect the pistons for scuffing, scoring, cranks, pitting, or excessive ring groove wear. If these are evident, the piston must be replaced.

The piston should also be checked in relation to the cylinder diameter. Using a telescoping gauge and micrometer, or a dial gauge, measure the cylinder bore diameter perpendicular (90%) to the piston pin, 2 1 / 2 in. below the cylinder block deck (surface where the block mates with the heads). Then, with the micrometer, measure the piston perpendicular to its wrist pin on the skirt. The difference between the two measurements is the piston clearance.

If the clearance is within specifications or slightly below (after the cylinders have been bored or honed), finish honing is all that is necessary. If the clearance is excessive, try to obtain a slightly larger piston to bring clearance to within specifications. If this is not possible obtain the first oversize piston and hone (or if necessary, bore) the cylinder to size. Generally, if the cylinder bore is tapered 0.005 in. or more or is out-of-round 0.003 in. or more, it is advisable to rebore for the smallest possible oversize piston and rings. After measuring, mark pistons with a felt-tip pen for reference and for assembly.

Cylinder block boring should be performed by a reputable machine shop with the proper equipment. In some cases, cleanup honing can be done with the cylinder block in the vehicle, but most excessive honing and all cylinder boring must be done with the block stripped and removed from the vehicle.

 
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