Pistons/Connecting Rods — Check (Mitsubishi Galant 5)

1. Before checking, pistons/connecting rods must be completely cleaned and old piston rings removed.

Note: Always use new piston rings when reassembling the engine.

2. Using a piston ring remover, carefully remove the rings from the pistons. Be careful not to damage the pistons in the process.



3. Remove all traces of carbon deposits from the top of the piston. You can use a hand wire brush or fine sandpaper for this, or scrape off particularly stubborn deposits. Under no circumstances should you use a wire brush attached to a drill to remove carbon deposits from the pistons. The piston material is quite soft and can be ground off with such a tool.

4. Use a special cleaning tool to remove carbon deposits from the piston grooves. If you don't have such a tool, a piece of an old broken piston ring will do. Remove only the carbon deposits - do not grind off the metal or scratch the edges of the grooves (see illustrations).





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5. After removing the carbon deposits, clean the pistons/connecting rods in solvent and dry them with compressed air (if possible). Check the cleanliness of the oil return holes on the back of the piston ring grooves.

6. If the pistons and cylinder walls are not damaged or excessively worn, and if the cylinder block has not been bored, there is no need to install new pistons. Normal piston wear is manifested as uniform vertical wear of the contact surface and a slight play of the upper ring in the groove. However, when assembling the engine, new piston rings must be used.

7. Carefully check each piston for cracks around the skirt, at the piston pin boss and near the ring grooves.

8. Check for scuffs on the bearing surface of the skirt, holes in the piston crown, and burnouts on the edge of the crown. If the skirt has scuffs or deep scratches, the engine may be overheating and/or has an abnormal combustion mode of the fuel mixture, which leads to an excessive increase in operating temperature. It is necessary to completely check the lubrication and cooling systems. A hole in the piston crown indicates abnormal combustion (early ignition). Burnout of the edges of the piston crown is usually a consequence of detonation. If any of the described problems are present, it is necessary to eliminate the cause, otherwise the malfunction will recur. The causes may be air leaks in the intake manifold, incorrect composition of the fuel-air mixture, incorrect ignition timing, and failure of the exhaust gas recirculation (EGR) system.



9. Piston corrosion in the form of small spots indicates that coolant is getting into the combustion chamber and/or crankcase. It is necessary to eliminate the cause so that this does not happen on a newly assembled engine.

10. Measure the piston ring side clearance by installing a new ring in the groove with a feeler gauge (see illustration). Check the clearance at three or four places around the circumference of each groove - they will vary from one to the other. If the side clearance is greater than the specification, new pistons must be installed.



11. Check the clearance between the piston and the cylinder by measuring the cylinder diameters (see section 18) and piston. Make sure that the pistons and cylinders fit together. Measure the diameter of the piston skirt perpendicular and along the piston pin at a distance of 2 mm above the lower edge of the piston (see illustration). Subtract the piston diameter from the cylinder liner diameter, which gives the clearance. If the clearance is greater than the specification, the block must be bored and new pistons and rings installed.





12. Check the piston-to-connecting rod clearance by moving the piston and connecting rod in opposite directions. Any noticeable play indicates excessive wear that must be corrected. The piston/connecting rod assemblies should be taken to a machine shop where the pistons and connecting rods can be rebored and new piston pins installed.

13. If for any reason the pistons need to be separated from the connecting rods, they should be taken to a car service workshop. While they are there, check the connecting rods for twisting and bending, as workshops have special equipment for this.

Note: Do not separate the pistons from the connecting rods unless you are installing new pistons and/or connecting rods.

14. Check the connecting rods for cracks and other damage. Temporarily remove the connecting rod caps, remove the old bearing shells, wipe the bearing surfaces of the connecting rods and caps clean and check for scratches, grooves and gouges. After checking the connecting rods, replace the old shells, reinstall the caps and tighten the nuts with finger force.

Note: If the engine is rebuilt due to connecting rod knocking, new connecting rods should be installed.