Chevrolet Full Size Cars 1979-1989

Pistons and Connecting Rods

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REMOVAL & INSTALLATION





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Fig. Fig. 1 If present, the cylinder ridge must be removed before the pistons are removed from the block



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Fig. Fig. 2 Match connecting rods to their caps using a scribe mark



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Fig. Fig. 3 Match the connecting rods to their cylinders using a number stamp



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Fig. Fig. 4 Cut lengths of rubber hose for connecting rod bolt guides



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Fig. Fig. 5 Carefully tap the piston and rod assembly out using a wooden hammer handle



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Fig. Fig. 6 Left bank piston and rod assembly 231 V6 engine



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Fig. Fig. 7 Inline 6-cylinder piston-to-rod relationship



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Fig. Fig. 8 Piston-to-rod relationship 262 V6 and small block Chevrolet produced engines

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. For more details, refer to the ridge removal and honing procedures later in this section.

  1. Remove intake manifold and cylinder head or heads.
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  3. Remove oil pan.
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  5. If necessary, remove the oil pump assembly.
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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 host to use as rod bolt guides. 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 and 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 V6 engines, starting at the front the cylinders are numbered 2-4-6 on the right bank and 1-3-5 on the left. On all V8s, starting at the front of the left bank the cylinders are numbered 1-3-5-7 and from the front of the right bank cylinders are 2-4-6-8.

  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 marks 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 AND INSPECTING





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



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



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Fig. Fig. 11 An 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 Cylinder bore measuring points



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Fig. Fig. 14 The cylinder bore may also be measured using a dial gauge

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 piston grooves using an appropriate ring groove cleaning tool, 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 degrees) 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, and/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 both reference and 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 car, but most excessive honing and all cylinder boring must be done with the block stripped and removed from the car.

RIDGE REMOVAL & HONING





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Fig. Fig. 15 Removing cylinder glazing using a flexible hone



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Fig. Fig. 16 Cylinder bore cross-hatch pattern



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Fig. Fig. 17 A properly cross-hatched cylinder bore

  1. Before the piston is removed from the cylinder, check for a ridge at the top of the cylinder bore. This ridge occurs because the piston ring does not travel all the way to the top of the bore, thereby leaving an unworn portion of the bore.
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  3. Clean away any carbon buildup at the top of the cylinder with sand paper, in order to see the extent of the ridge more clearly. If the ridge is slight, it will be safe to remove the pistons without damaging the rings or piston ring lands. If the ridge is severe, and easily catches your fingernail, it will have to be removed using a ridge reamer.
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A severe ridge is an indication of excessive bore wear. Before removing the piston, check the cylinder bore diameter with a bore gauge, as explained in the cleaning and inspection procedure. Compare your measurement with engine specification. If the bore is excessively worn, the cylinder will have to bored oversize and the piston and rings replaced.

  1. Install the ridge removal tool in the top of the cylinder bore. Carefully follow the manufacturers instructions for operation. Only remove the amount of material necessary to remove the ridge. 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.
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WARNING
Be very careful if you are unfamiliar with operating a ridge reamer. It is very easy to remove more cylinder bore material than you want, possibly requiring a cylinder overbore and piston replacement that may not have been necessary.

  1. After the piston and connecting rod assembly have been removed, check the clearances as explained earlier in this section under the cleaning and inspection procedure, to determine whether boring and honing or just light honing are required. If boring is necessary, consult an automotive machine shop. If light honing is all that is necessary, proceed with the next step.
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  3. Honing is best done with the crankshaft removed, to prevent damage to the crankshaft and to make post-honing cleaning easier, as the honing process will scatter metal particles. However, if you do not want to remove the crankshaft, position the connecting rod journal for the cylinder being honed as far away from the bottom of the cylinder bore as possible, and wrap a shop cloth around the journal.
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  5. Honing can be done either with a flexible glaze breaker type hone or with a rigid hone that has honing stones and guide shoes. The flexible hone removes the least amount of metal, and is especially recommended if your piston-to-cylinder bore clearance is on the loose side. The flexible hone is useful to provide a finish on which the new piston rings will seat. A rigid hone will remove more material than the flexible hone and requires more operator skill.
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  7. Regardless of which type of hone you use, carefully follow the manufacturers instructions for operation.
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  9. The hone should be moved up and down the bore at sufficient speed to obtain a uniform finish. A rigid hone will provide a definite cross-hatch finish; operate the rigid hone at a speed to obtain a 45-65 degree included angle in the crosshatch. The finish marks should be clean but not sharp, free from embedded particles and torn or folded metal.
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  11. Periodically during the honing procedure, thoroughly clean the cylinder bore and check the piston-to-bore clearance with the piston for that cylinder.
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  13. After honing is completed, thoroughly wash the cylinder bores and the rest of the engine with hot water and detergent. Scrub the bores well with a stiff bristle brush and rinse thoroughly with hot water. Thorough cleaning is essential, for if any abrasive material is left in the cylinder bore, it will rapidly wear the new rings and the cylinder bore. If any abrasive material is left in the rest of the engine, it will be picked up by the oil and carried throughout the engine, damaging bearings and other parts.
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  15. After the bores are cleaned, wipe them down with a clean cloth coated with light engine oil, to keep them from rusting.
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PISTON RING AND WRIST PIN





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Fig. Fig. 18 Exploded view of a common piston and wrist pin assembly



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Fig. Fig. 19 Removing wrist pin snaprings



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Fig. Fig. 20 Ring gap locations for all gasoline engines except the 231 V6. For diesel engine ring gaps, refer to the diagram supplied with the replacement rings.



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Fig. Fig. 21 Piston wring gap location 231 V6 engine



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Fig. Fig. 22 Checking piston ring end gap using a feeler gauge



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Fig. Fig. 23 Checking ring side clearance on a piston from a gasoline engine



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Fig. Fig. 24 Most rings are marked to show which side should face upward

Removal

Some of the engines covered in this guide utilize pistons with pressed-in wrist pins; these must be removed by a special press designed for this purpose. Other pistons have their wrist pins secured by snaprings, which are easily removed with snapring pliers. Determine which piston type your engine is equipped with and separate the piston from the connecting rod using the appropriate method.

A piston ring expander is necessary for removing piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the rings 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 tool, 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 pistons. Inspect the pistons for scuffing, scoring, cracks, 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 degrees) 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, and/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 both reference and assembly.

After measuring, mark pistons with a felt-tip pen for reference and for assembly.

Cylinder honing and/or boring should be performed by a reputable, professional mechanic with the proper equipment. In some cases, clean-up honing can be done with the cylinder block in the car, but most excessive honing and all cylinder boring must be done with the block stripped and removed from the car.

Piston Ring End Gap

Piston ring end gap should be checked while the rings are removed from the pistons. Incorrect end gap indicates the wrong size rings are being used; ring breakage could occur and engine damage could result.

Squirt clean engine oil into the cylinder, then carefully compress and insert the piston rings to be used in a cylinder, one at a time, into that cylinder. Position the rings approximately 1 in. below the deck of the block (on diesels, measure ring gap clearance with the ring positioned at the bottom of ring travel in the bore). The ring can be carefully positioned using the top of the piston, this will assure that the ring is properly squared to the cylinder walls. Measure the ring end gap with a feeler gauge, and compare to the piston and ring chart earlier in this section. Carefully pull the ring out of the cylinder and, if a larger clearance is necessary, file the ends squarely with a fine file to obtain the proper clearance.

Piston Ring Side Clearance Check & Installation

Check the pistons to see that the ring grooves and oil return holes have been properly cleaned. Slide a piston ring into its groove, and check the side clearance with a feeler gauge. On gasoline engines, make sure you insert the gauge between the ring and its lower land (lower edge of the groove), because any wear that occurs forms a step at the inner portion of the lower land. On diesels, insert the gauge between the ring and the upper land. If the piston grooves have worn to the extent that relatively high steps exist on the lower land, the piston should be replaced, because these will interfere with the operation of the new rings and ring clearance will be excessive. Piston ring are not furnished in oversize widths to compensate for ring groove wear.

Install the rings on the piston, lowest ring first, using a piston ring expander. There is a high risk of breaking or distorting the rings, or scratching the piston, if the rings are installed by hand or other means.

Position the rings on the piston as illustrated; spacing of the various piston ring gaps is crucial to proper oil retention and even cylinder wear. When installing new rings, refer to the installation diagram furnished with the new parts.

ROD BEARING REPLACEMENT





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Fig. Fig. 25 Apply a strip of gauging material to the bearing



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Fig. Fig. 26 Install the bearing cap and tighten to specification



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Fig. Fig. 27 Remove the bearing cap and compare the gauging material to the scale provided with the package



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Fig. Fig. 28 Always oil the bearings prior to installation



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Fig. Fig. 29 The line on the scale that is closest to the thickness of the gauging material represents the bearing clearance

Connecting rod bearings for the engines covered in this guide consist of two halves or shells which are interchangeable in the rod and cap. When the shells are placed in position, the ends extend slightly beyond the rod and cap surfaces so that when the rod bolts are torqued the shells will be clamped tightly in place to insure positive seating and to prevent turning. A tang holds the shells in place.

The ends of the bearing shells must never be filed flush with the mating surface of the rod and cap.

If a rod bearing becomes noisy or is worn so that its clearance on the crank journal is sloppy, a new bearing of the correct undersize must be selected and installed since there is no provision for adjustment.


WARNING
Under no circumstances should the rod end or cap be filed to adjust the bearing clearance, nor should shims of any kink be used.

Inspect the rod bearings while the rod assemblies are out of the engine. If the shells are scored or show flaking, they should be replaced. If they are in good shape check for proper clearance on the crank journal (see below). Any scoring or ridges on the crank journal means the crankshaft must be replaced, or reground and fitted with undersized bearings.

If turbo V6 crank journals are scored or ridged the crankshaft must be replaced, as regrinding will reduce the durability of the crankshaft.

Checking Bearing Clearance and Replacing Bearings

Make sure connecting rods and their caps are kept together, and that the caps are installed in the proper direction

Replacement bearings are available in standard size, and in undersizes for reground crankshaft. Connecting rod-to-crankshaft bearing clearance is checked using Plastigage® or an equivalent gauging material at either the top or bottom of each crank journal. The Plastigage® has a range of 0.001-0.003 in.

  1. Remove the rod cap with the bearing shell. completely clean the bearing shell and the crank journal, and blow any oil from the oil hole in the crankshaft; Plastigage® is soluble in oil.
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  3. Place a piece of Plastigage® lengthwise along the bottom center of the lower bearing shell, then install the cap with shell and torque the bolt or nuts to specification. DO NOT turn the crankshaft with Plastigage® in the bearing.
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  5. Remove the bearing cap with the shell. the flattened Plastigage® will be found sticking to either the bearing shell or crank journal. Do not remove it yet.
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  7. Use the scale printed on the Plastigage® envelope to measure the flattened material to its widest point. The number within the scale which most closely corresponds to the width of the Plastigage® indicates bearing clearance in thousandths of an inch.
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  9. Check the specifications chart earlier this section for the desired clearance. It is advisable to install a new bearing if clearance exceeds 0.003 in.; however, if the bearing is in good condition and is not being checked because of bearing noise, bearing replacement is not necessary.
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  11. If you are installing new bearings, try a standard size, then each undersize in order until one is found that is within the specified limits when checked for clearance with Plastigage®. Each undersize shell has its size stamped on it.
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  13. When the proper size shell is found, clean off the Plastigage® and oil the bearing thoroughly, then reinstall the cap with its shell and torque the rod fasteners to specification.
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With the proper bearing selected and the nuts torqued, it should be possible to move the connecting rod back and forth freely on the crank journal as allowed by the specified connecting rod end clearance. If the rod cannot be moved, either the rod bearing is too far undersize or the rod is misaligned.

ASSEMBLY AND INSTALLATION





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Fig. Fig. 30 Piston locations in block diesel engine



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Fig. Fig. 31 Using a wooden hammer handle, carefully tap the piston down through the ring compressor and into the cylinder bore



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Fig. Fig. 32 Check the connecting rod side clearance using a feeler gauge. A small prybar should be used to carefully spread the connecting rods.

Install the connecting rod to the piston, making sure the piston installation notches and any marks on the rod are in proper relation to one another. Lubricate the wrist pin with clean engine oil, and install the pin into the rod and piston assembly, either by hand or by using a wrist pin press as required. If equipped, install the snaprings and rotate them in their grooves to make sure they are seated. Once the piston and connecting rod assembly is prepared, it may be installed to the block and crankshaft.

  1. Make sure connecting rod big-end bearings (including end cap) are of the correct size and properly installed.
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  3. Fit rubber hoses over the connecting rod bolts to protect the crankshaft journals, as done during removal. Coat the rod bearings with clean oil.
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It is a good idea to lightly coat the walls of the cylinder bore with clean engine oil during assembly.

  1. Using the proper ring compressor, insert the piston assembly into the cylinder so that the notch in the top of the piston faces the front of the engine (this assumes that the dimple(s) or other markings on the connecting rods are in correct relation to the piston notch(s). The marks made during disassembly should serve as a guide here.
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  3. From beneath the engine, coat each crank journal with clean oil. Pull the connecting rod, with the bearing shell in place, into position against the crank journal.
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  5. Remove the rubber hoses. Install the bearing cap and cap nuts, then torque to specification.
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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 ease the installation of the remaining piston assemblies.

  1. Check the clearance between the sides of the connecting rods and the crankshaft using a feeler gauge. Spread the rods slightly with a small prybar and insert the gauge. If clearance is below the minimum tolerance, the rod may be machined to provide adequate clearance. If clearance is excessive, substitute an unworn rod, and recheck. If clearance is still outside specifications, the crankshaft must be welded and reground, or replaced.
  2.  
  3. Replace the oil pump if removed and the oil pan.
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  5. Install the cylinder head(s) and intake manifold.
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