Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Pistons and Connecting Rods

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This procedure requires removal of the cylinder head and oil pan. It is much easier to perform this work with the engine removed from the vehicle and mounted on a stand.These procedures require certain hand tools which may not be in your tool box. A cylinder ridge reamer, a numbered punch set, piston ring expander, snapring tools and piston installation tool (ring compressor) are all necessary for correct piston and rod repair.

REMOVAL



See Figures 1 through 9

  1. Remove the cylinder head, following correct procedures listed earlier in this section.
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  3. Remove the oil pan, following correct procedures listed earlier in this section.
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  5. The connecting rods are marked to indicate which surface faces front, but the bearing caps should be matchmarked with numbers (front to rear) before disassembly. Use a marking punch and a small hammer; install the number over the seam so that each piece will be re-used in its original location.
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  7. Remove the connecting rod cap bolts, pull the caps off the rods, and place them on a bench in order.
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Fig. Fig. 1: Exploded view of pistons, connecting rods and related parts-2.6L engine



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Fig. Fig. 2: Mark the side of the piston rod and rod cap with the cylinder number



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Fig. Fig. 3: Place lengths of rubber hose over the connecting rod studs in order to protect the crankshaft and cylinders from damage



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Fig. Fig. 4: Carefully tap the piston out of the bore using a wooden dowel



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Fig. Fig. 5: Use a ring expander tool to remove the piston rings



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Fig. Fig. 6: Clean the piston grooves using a ring groove cleaner



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Fig. Fig. 7: A piece of an old ring can be used to clean out the grooves, BUT be careful-the ring is very sharp



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Fig. Fig. 8: Remove the glazing on the cylinder walls with a flexible drill hone



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Fig. Fig. 9: Remove the ridge from the cylinder bore using a ridge cutter

  1. Inspect the upper portions of the cylinder (near the head) for a ridge formed by ring wear. If there is a ridge, it must be removed by first shifting the piston down in the cylinder and then covering the piston top completely with a clean rag. Use a ridge reamer to remove metal at the lip until the cylinder is smooth. If this is not done, the rings will be damaged during removal of the piston.
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  3. Once the ridges have been removed, the pistons and rods may be pushed upward and out of the cylinders. Place pieces of rubber tubing over the rod bolts to protect the cylinder walls. Use a piece of wood or a hammer handle under the piston to tap it upward.If you're working under an engine that's still installed in the vehicle with the crankshaft still in position, turn the crankshaft until the crankpin for each cylinder is in a convenient position. Be careful not to subject the piston and/or rod to heavy impact and do not allow the piston rod to damage the cylinder wall on the way out. The slightest nick in the metal can cause problems after reassembly.
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  5. Clean the pistons, rings and rods in parts solvent with a bristle brush. Do not use a wire brush, even to remove heavy carbon. The metal may be damaged. Use a piston groove cleaner to clean the lands (grooves) in the piston.
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INSPECTION



See Figures 10, 11, 12 and 13

  1. Measure the bore of the cylinder at three levels and in two dimensions (fore-and-aft and side-to-side). That's six measurements for each cylinder. By comparing the three vertical readings, the taper of the cylinder can be determined and by comparing the front-rear and left-right readings the out-of-round can be determined. The block should be measured: at the level of the top piston ring at the top of piston travel; in the center of the cylinder; and at the bottom. Compare your readings with the specifications in the chart.
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  3. If the cylinder bore is within specifications for taper and out-of-round, and the wall is not scored or scuffed, it need not be bored. If not, it should be bored oversize as necessary to ensure elimination of out-of-round and taper. Under these circumstances, the block should be taken to a machine shop for proper boring by a qualified machinist using the specialized equipment required.
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If the cylinder is bored, oversize pistons and rings must be installed. Since all pistons must be the same size (for correct balance within the engine) ALL cylinders must be re-bored if any one is out of specification.

  1. Even if the cylinders need not be bored, they should be fine honed for proper break-in by a qualified machine shop. A de-glazing tool may be used in a power drill to remove the glossy finish on the cylinder walls. Use only the smooth stone type, not the beaded or bottle-brush type.
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  3. The cylinder head top deck (gasket surface) should be inspected for warpage. Run a straightedge along all four edges of the block, across the center, and diagonally. If you can pass a feeler gauge of 0.004 in. (0.1mm) under the straightedge, the top surface of the block should be machined.
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  5. The rings should be removed from the pistons with a ring expander. Keep all rings in order and with the piston from which they were removed. The rings and piston ring grooves should be cleaned thoroughly with solvent and a brush as deposits will alter readings of ring wear.
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  7. Before any measurements are begun, visually examine the piston for any signs of cracks, particularly in the skirt area or scratches in the metal. Anything other than light surface scoring disqualifies the piston from further use. The metal will become unevenly heated and the piston may break apart during use.
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Fig. Fig. 10: Measure the inside bore of the cylinders



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Fig. Fig. 11: Inspect the top deck of the block in the directions shown



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Fig. Fig. 12: Measuring piston ring side clearance



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Fig. Fig. 13: Use an inverted piston to seat a ring in the cylinder-measure the end-gap with a feeler gauge

  1. Piston diameter should be measured at the skirt, at right angles to the piston pin. Compare either with specified piston diameter or subtract the diameter from the cylinder bore dimension to get clearance, depending upon the information in the specifications.If clearance is excessive, the piston should be replaced. If a new piston still does not produce piston-to-wall clearance within specifications, use an oversize piston and bore out the cylinder accordingly.
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  3. Compression ring side clearance should be measured by using a ring expander to put cleaned rings back in their original positions on the pistons. Measure side clearance on one side by attempting to slide a feeler gauge of the thickness specified between the ring and the edge of the ring groove. If the gauge will not pass into the groove, the ring may be re-used. If the gauge will pass, but a gauge of slightly greater thickness representing the wear limit will not, the piston may be re-used, but new rings must be installed.
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  5. Ring end-gap must be measured for all three rings in the cylinder by using a piston top (upside down) to press the ring squarely into the top of the cylinder. The rings must be at least 0.59 in. (15mm) from the bottom of the bore. Use a feeler gauge to measure the end-gap and compare it with specifications.If cylinder bore wear is very slight, you may use new rings to bring the end-gap to specification without boring the cylinder. Measure the gap with the ring located near the minimum dimension at the bottom of the cylinder, not nearer the top where wear is greatest.
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  7. The connecting rods must be free from wear, cracking and bending. Visually examine the rod, particularly at its upper and lower ends. Look for any sign of metal stretching or wear. The piston pin should fit cleanly and tightly through the upper end, allowing no side-play or wobble. The bottom end should also be an exact half-circle, with no deformity of shape. The bolts must be firmly mounted and parallel.The rods may be taken to a machine shop for exact measurement of twist or bend.
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INSTALLATION



See Figures 14, 15, 16, 17, 18, 19 and 20

  1. Remember that if you are installing an oversize piston, you must also use new rings that are also of the correct oversize.
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  3. Install the rings on the piston, lowest ring first. Generally the side rails for the oil control ring can be installed by hand with care. The other rings require the use of the ring expander. There is a high risk of ring breakage or piston damage if the rings are installed without the expander. The correct spacing of the ring end-gaps is critical to oil control.No two gaps should align; they should be evenly spaced around the piston with the gap in the oil ring expander facing the front of the piston (aligned with the mark on the top of the piston). Once the rings are installed, the pistons must be handled carefully and protected from dirt and impact.
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Fig. Fig. 14: Most rings are marked to show which side should face upward



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Fig. Fig. 15: Stagger the ring gap when installing



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Fig. Fig. 16: Piston ring installation-2.3L diesel engine



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Fig. Fig. 17: Piston installation-2.3L diesel engine



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Fig. Fig. 18: Install the rings with the marks upward-the barrel faced chrome plated ring goes in the No. 1 position while the taper type goes in position No. 2



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Fig. Fig. 19: Piston identification marks-the V6 pistons use L and R depending on which bank contained the piston



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Fig. Fig. 20: Installing the piston into the block using a ring compressor and the handle of a hammer

  1. Install the number two compression ring next and then the top compression ring using a ring expander. Note that these rings have the same thickness but different cross-sections; make sure positioning is correct. Make sure all markings face upward and that the gaps are all staggered. Gaps must also not be in line with either the piston pin or thrust faces of the piston.
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  3. All the pistons, rods and caps must be reinstalled in the correct cylinder. Make certain that all labels and stamped numbers are present and legible. Double check the piston rings; make certain that the ring gaps DO NOT line up, but are evenly spaced around the piston at about 120° intervals. Double check the bearing insert at the bottom of the rod for proper mounting. Reinstall the protective rubber hose pieces on the bolts.
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  5. Liberally coat the cylinder walls and the crankshaft journals with clean, fresh engine oil. Also apply oil to the bearing surfaces on the connecting rod and the cap.
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  7. Identify the front mark on each piston and rod and position the piston loosely in its cylinder with the marks facing the front (pulley end) of the motor.
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WARNING
Failure to observe the "Front" marking and its correct placement can lead to sudden engine failure.

  1. Install the ring compressor (piston installation tool) around one piston and tighten it gently until the rings are compressed almost completely.
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  3. Gently push down on the piston top with a wooden hammer handle or similar soft-faced tool and drive the piston into the cylinder bore. Once all three rings are within the bore, the piston will move with some ease.
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WARNING
If any resistance or binding is encountered during the installation, DO NOT apply force. Tighten or adjust the ring compressor and/or reposition the piston. Brute force will break the ring(s) or damage the piston.

  1. From underneath, pull the connecting rod into place on the crankshaft. Remove the rubber hoses from the bolts. Check the rod cap to confirm that the bearing is present and correctly mounted, then install the rod cap (observing the correct number and position) and its nuts. Leaving the nuts finger-tight will make installation of the remaining pistons and rods easier.
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  3. Assemble the remaining pistons in the same fashion, repeating steps 7, 8 and 9.
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  5. With all the pistons installed and the bearing caps secured finger-tight, the retaining nuts may be tightened to their final setting. Refer to the torque specifications chart for the correct torque for the engine in your vehicle. For each pair of nuts, make three passes alternating between the two nuts on any given rod cap. The three tightening steps should each be about one third of the final torque. The intent is to draw each cap up to the crank straight and under even pressure at the nuts.
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  7. Turn the crankshaft through several clockwise rotations, making sure everything moves smoothly and there is no binding. With the piston rods connected, the crank may be stiff to turn. Try to turn it in a smooth continuous motion so that any binding or stiff spots may be felt.
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  9. Reinstall the oil pan. Even if the engine is to remain apart for other repairs, install the oil pan to protect the bottom end and tighten the bolts to the correct specification; this eliminates one easily overlooked mistake during future reassembly.
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  11. If the engine is to remain apart for other repairs, pack the cylinders with crumpled newspaper or clean rags (to keep out dust and grit) and cover the top of the motor with a large rag. If the engine is on a stand, the whole block can be protected with a large plastic trash bag.
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  13. If no further work is to be performed, continue reassembly by installing the head, timing belt, etc.
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PISTON PIN (WRIST PIN) REPLACEMENT



See Figures 21, 22, 23, 24 and 25

The piston and pin are a matched set and must be kept together. Label everything and store parts in identified containers.The use of the correct special tools or their equivalent is very important for this procedure. You will need tool set MD 998184-01 for removing and installing the piston pin. You will also need access to a hydraulic press, capable of delivering up to 4000 lbs. (17,792 N) of force.

  1. Remove the pistons from the engine and remove the rings from the pistons.
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  3. Set up the tool set with the pin pusher on the press bed. Make certain the press plates are securely fastened to the press frame.
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  5. Fit the piston and rod assembly onto the body of the special tool, with the front marks on the rod and piston facing up. The numbers or letters on the side of the rod serve as the front mark for the rod; the piston usually has an arrowhead pointing to the front. The V6 pistons are marked "L" and "R"; if the piston came from the left (firewall) side, the "L" designates the front. If from the right bank, use the "R" as the front marker.
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  7. Position the piston so that the lip of the tool insert fits between the connecting rod boss and the inside of the piston. The boss should contact as much of the tool insert as possible to support it.
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  9. Adjust the support at the rear of the connecting rod until the rod is horizontal (level) to the press bed. Misalignment of the pin and receiving tube may occur if the rod is crooked.
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  11. Position the pin pusher on the pin and use the press to drive the pin out. As the pin is removed, it must pass through the receiving tube. Adjust the alignment as necessary.
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  13. Remove the rod and piston from the press. Check the pin for obvious wear or damage. A quick check of piston pin wear is to push the pin into the piston (without the rod) with your thumb. The pin should fit with slight resistance. If the pin is too loose or has any play, either the pin or piston is worn; both should be replaced.
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Fig. Fig. 21: Assemble the piston pin tools onto hydraulic press



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Fig. Fig. 22: The insert will support the rod during removal and installation



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Fig. Fig. 23: Adjust the rear support so the rod is horizontal and parallel to the press bed



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Fig. Fig. 24: Install the spring, spacer and guide into the receiving tube



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Fig. Fig. 25: The clearance measurement is important-the pin must be centered after installation

  1. To reinstall, set up the special press tools with the stop plug threaded about halfway into the bottom of the receiving tube.
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  3. Select the largest piston pin guide that will pass through the piston and rod. Install the spring, spacer and guide into the receiving tube.
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  5. With the connecting rod removed from the piston, insert the piston pin into the piston so that it is centered in the piston. Accurately measure the amount of protrusion (or recess) between the pin and piston and make certain the measurement is the same on the opposite side. Record the measurement.
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  7. Place the connecting rod and piston over the special tool on the press with the front marks facing up. The spring loaded piston guide will pass through the piston and rod and align them.
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  9. Coat the piston pin with fresh motor oil and install it into the piston. Place the pin pusher on the piston pin and use the press to insert it through the connecting rod and opposite side of the piston.
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  11. Continue pressing until the pin projection (or recess) is equal to that measured in Step 10. apply pressure to the pin and adjust the stop plug until it comes into contact with the spacer.
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  13. Remove the piston assembly from the press and check the piston pin for centering. If it is not centered, adjust the stop plug up or down to obtain the correct position. The pin stop is now set for any remaining pistons.
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WARNING
Installation pressure on the press ranges from about 1100 lbs. (4,893 N) to about 3600 lbs. (16,013 N). If the pin cannot be installed within this range, replace the rod and/or pin. Pressure extremes will break the piston or rod.

ROD BEARING REPLACEMENT



See Figures 26, 27, 28 and 29

  1. Crankshaft crankpins (the part of the crank on which the bearing rides) should be inspected for clogged oil holes and scoring. If scoring is evident, the crankpins should be machined undersize and the proper undersize (thicker) bearings installed in all the rods.
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  3. If the crankpins and rod bearing shells appear to show minimal wear and normal wear patterns, they still must be checked for proper fit with Plastigage®. Clean all the surfaces of oil and then cut plastic measuring media (Plastigage® or similar) inserts to a length that will fit the width of the bearing. Apply the insert to an area of the crankpin away from an oil hole and install the rod cap. Tighten the bolts to specification. Make sure you don't turn the crankshaft.
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Fig. Fig. 26: Apply a strip of gauging material to the bearing journal, then install and tighten the cap



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Fig. Fig. 27: Reading the width of the mark left by Plastigage®



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Fig. Fig. 28: Checking connecting rod side clearance



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Fig. Fig. 29: Notches in the connecting rod and connecting rod cap should be on the same side

  1. Remove the connecting rod bolts and then remove the caps. Read the width of the Plastigage® at its widest part by comparing it with the scale on the package to get actual bearing clearance. If the bearing clearance is within specification, the bearings may be reused.
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  3. You must also measure side clearance between the connecting rod side surface and the crank with the rod assembled and tightened to the specified torque. Excessive wear here indicates the rod and cap must be replaced to restore clearance.
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  5. When the bearing shells are replaced, make sure bearing backs and inner surfaces of the rod and cap are dry and that bearings and crankpins are well lubricated with clean engine oil. It is important to insure that all bearings are installed with the notches (in the bearings, rod and cap) aligned; this will keep the bearing from spinning out of position.Notches in the rod and cap should be on the same side. This is a way to make sure rod and cap are properly assembled.
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  7. Tighten the rod bolts to specification, going back and forth in several steps.
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