Dodge Colt/Challenger/Conquest/Vista 1971-1989 Repair Guide

Pistons and Connecting Rods

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REMOVAL & INSTALLATION





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Fig. Fig. 1 Cylinder bore ridge



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Fig. Fig. 2 Install a ring compressor around the piston, then install the assembly into the block as shown

Although, in most cases, the pistons and connecting rods can be removed from the engine (after the cylinder head and oil pan are removed) while the engine is still in the car: it is far easier to work on the engine when removed from the car.

If removing pistons with the engine still installed, disconnect the radiator hoses, automatic transmission cooler lines and radiator shroud. Unbolt front mounts before jacking up the engine and block the engine in position with wooden blocks between the mounts.

  1. Remove the engine from the car. Remove cylinder head, oil pan and front cover.
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  3. Because the top piston ring does not travel to the very top of the cylinder bore, a ridge is built up between the end of the travel and the top of the cylinder. Pushing the piston and connecting rod assembly past the ridge is difficult and may cause damage to the piston. If new rings are installed the ridge has not been removed, ring breakage and piston damage can occur when the ridge is encountered at engine speed.
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  5. Turn the crankshaft to position the piston at the bottom of the cylinder bore. Cover the top of the piston with a rag. Install a ridge reamer in the bore and follow the manufacture's instructions to remove the ridge. Use caution, avoid cutting too deeply. Remove the rag and cutting from the top of the piston. Remove the ridge from all cylinders.
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  7. Check the edges of the connecting rod and bearing cap for numbers or matchmarks, if none are present mark the rod and cap numerically and in sequence from front to back of engine. The numbers or marks not only tell from which cylinder the piston came from but also helps ensure that the rod caps are installed in the correct matching position.
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  9. Turn the crankshaft until the connecting rod is at the bottom of travel. Remove the two attaching nuts and the bearing cap. Take two pieces of rubber tubing and cover the rod bolts to prevent crank or cylinder scoring. Use a wooden hammer handle to help push the piston and rod up and out of the cylinder. Reinstall the rod cap in proper position. Remove all pistons and connecting rods. Inspect cylinder walls and deglaze or hone as necessary.
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  11. Lubricate each piston, rod bearing and cylinder wall. Install a ring compressor over the piston, position the piston with mark toward front of engine and carefully install it into engine. Tap the piston into the bore with a wooden hammer handle or rubber hammer. Position connecting rod with bearing insert installed over the crank journal. Install the rod cap with bearing in proper position. Secure with rod nuts and torque to proper specifications. Install all of the remaining piston assemblies.
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CLEANING AND INSPECTION





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



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



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Fig. Fig. 5 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. 6 A telescoping gauge may be used to measure the cylinder bore diameter



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

  1. Use a piston ring expander and remove the rings from the piston.
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  3. Clean the ring grooves using an appropriate cleaning tool, exercise care to avoid cutting too deeply.
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  5. Clean all varnish and carbon from the piston with a safe solvent. Do not use a wire brush or caustic solution on the pistons.
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  7. Inspect the pistons for scuffing, scoring, cracks, pitting or excessive ring groove wear. If wear is evident, the piston must be replaced.
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  9. Have the piston and connecting rod assembly checked by a machine shop for correct alignment, piston pin wear and piston diameter. If the piston had Collapsed it will have to be replaced or knurled to restore original diameter. Connecting rod bushing replacement, piston pin fitting and piston changing can be handled by the machine shop.
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CYLINDER BORE





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Fig. Fig. 8 Using a gauge, check the piston ring and cap for wear



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Fig. Fig. 9 Removing cylinder glazing using a flexible hone



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Fig. Fig. 10 As with a ball hone, work the hone carefully up and down the bore to achieve the desired results

Check the cylinder bore for wear using a telescope gauge and a micrometer, measure the cylinder bore diameter perpendicular to the piston pin at a point 63.5mm below the top of the engine block. Measure the piston skirt perpendicular to the piston pin. The difference between the two measurements is the piston clearance. If the clearance is within specifications, finish honing or glaze breaking is all that is required. If clearance is excessive a slightly oversize piston may be required. If greatly oversize, the engine will have to be bored and 0.25mm or larger oversized pistons installed.

PISTON PINS





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Fig. Fig. 11 A solid hone can also be used to cross-hatch the cylinder bore



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

The pin connecting the piston and connecting rod is press fitted. If too much free-play develops take the piston assemblies to the machine shop and have oversize pins installed. Installing new rods or pistons requires the use of a press. Have the machine shop handle the job for you.

FITTING AND POSITIONING PISTON RINGS





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



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Fig. Fig. 14 Check the piston side clearance with a feeler gauge



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Fig. Fig. 15 Piston ring installation order



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Fig. Fig. 16 Piston ring positioning

  1. Take the new piston rings and care install, one at a time into the cylinder that they will be used in. Push the ring about 25mm below the top of the cylinder block using an inverted piston.
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  3. Use a feeler gauge and measure the distance between the ends of the ring, this is called measuring the ring end-gap. Compare the reading to the one called for in the specifications table. File the ends of the ring with a fine file to obtain necessary clearance.
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If inadequate ring end-gap is utilized, ring breakage will result.

  1. Inspect the ring grooves on the piston for excessive wear or taper. If necessary have the grooves recut for use with a standard ring and spacer. The machine shop can handle the job for you.
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  3. Check the ring groove by rolling the new piston ring around the groove to check for burrs or carbon deposits. If any are found, remove with a fine file. Hold the ring in the groove and measure side clearance with a feeler gauge. If clearance is excessive, spacer(s) will have to be added.
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Always add spacers above the piston ring.

  1. Install the rings on the piston, lower ring first using a ring installing tool. Consult the instruction sheet that comes with the rings to be sure they are installed with the correct side up. A mark on the ring usually faces upward.
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  3. When installing oil rings: install the center spreader (ring) in the groove. Hold the ends of the ring butted together (they must not overlap) and install the bottom rail (scraper) with the end about 25mm away from the butted end of the control ring. Install the top rail about 25mm away from the butted end of the control but on the opposite side from the lower rail.
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  5. Install the two compression rings (the rings usually have a stamped marked that faces up).
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  7. Consult the illustration with piston ring set instruction sheet for ring positioning, arrange the rings as shown, install a ring compressor and insert the piston and rod assembly into the engine.
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ROD BEARING REPLACEMENT





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Fig. Fig. 17 Place rubber hose over the connecting rod studs to protect the crank and bores from damage

  1. Rod bearings can be installed when the pistons have been removed for servicing (rings etc) or, in most cases, while the engine is still in the car. Bearing replacement, however, is far easier with the engine out of the car and disassembled.
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  3. For in car service, remove the oil pan, spark plugs and front cover if necessary, Turn the engine until the connecting rod to be serviced is at the bottom of its travel. Remove the bearing cap, place two pieces of rubber hose over the rod cap bolts and push the piston and rod assembly up the cylinder bore until enough room is gained for bearing insert removal. Take care not to push the rod assembly up too far or the top ring will engage the cylinder ridge or come out of the cylinder and require head removal for reinstallation.
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  5. Clean the rod journal, the connecting rod end and the bearing cap after removing the old bearing inserts. Install the new inserts in the rod and bearing cap, lubricate them with oil. Position the rod over the crankshaft journal and install the rod cap. Make sure the cap and rod numbers match, torque the rod nuts to specifications.
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  7. Install the front cover, oil pan, etc.
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