Note. Piston rings must be replaced without fail.
2. Using a special tool, remove the rings from the pistons - try not to accidentally damage the walls of the latter.
3. Scrape off any carbon deposits from the piston crowns. After removing the main layer of deposits, sand the surface by hand with a wire brush or a piece of fine sandpaper.
Note. Under no circumstances should wire attachments for an electric drill be used to clean pistons made of soft material and easily eroded!
4. Using a special tool, clean the grooves for the installation of rings on the pistons. Alternatively, you can use a piece of an old piston ring for this purpose, but be careful not to scratch the bottom and walls of the groove and do not cut your fingers.
5. After removing the main deposits, wash the connecting rod assemblies with a solvent and dry them thoroughly, if possible using compressed air. Check the patency of the oil return holes in the rear walls of the grooves for the installation of piston rings, as well as the oil holes in the lower heads of the connecting rods.
Attention! Remember to wear protective goggles when using compressed air!
6. If the piston walls and cylinder bores are not damaged or excessively worn, and the engine block has not been machined or replaced, there is no need to replace the pistons either. Normal wear of the pistons is manifested in the form of vertical wear marks along the thrust surface and a slight slack in the fit of the upper compression ring in its groove. Do not forget that the replacement of piston rings is mandatory, regardless of their condition.
7. Carefully inspect each of the pistons for cracks in the skirt, around the protrusions for the installation of piston pins and in the area of \u200b\u200bthe rings.
8. Check the thrust surfaces of the piston skirt for scratches, the bottom for through holes and burnouts along the edge. The presence of scratches on the skirt can be regarded as a sign of prolonged overheating of the engine, or too early ignition of the air-fuel mixture - check the correct functioning of the cooling system. Burnouts along the edges of the bottom are evidence of detonation. In any case, the cause of the identified violation must be eliminated in order to avoid relapses. Intake air leaks, incorrect air-fuel mixture layout, incorrect ignition timing, incorrect functioning of ignition and EGR systems can also be possible reasons for the formation of the listed defects.
9. Pitting of pistons in the form of cavities indicates that coolant has entered the combustion chambers and / or crankcase of the engine. Again, make sure that the cause of the internal leaks is corrected.
10. Assess the backlash of the piston rings in their grooves by inserting a new ring from the outside into your groove on the piston and using a blade-type feeler gauge to measure the remaining gap. Repeat the measurement at two or three points along the perimeter of the groove. Be careful not to mix up the compression rings - the top one is different from the second one. If the gap exceeds the allowable value (see specs), pistons must be replaced.
11. Determine the clearance of the pistons in your cylinders, for which measure the diameters of the latter (see Section Block Status Check) and subtract from them the diameters of the corresponding pistons. The piston diameter is measured along the thrust surface at an angle of 90°to the axis of the piston pin and at a given distance from the bottom. If the piston clearance in the cylinder exceeds the allowable value (see specs), the block should be given to the groove with a selection of new pistons and piston rings of a repair diameter.
12. Assess the correct fit of the pistons on the connecting rods by trying to rotate the components in opposite directions. The presence of any noticeable play indicates excessive wear on the joint. To correct the situation, the connecting rod and piston assemblies should be delivered to a car service workshop, where the necessary refurbishment and replacement of fingers will be carried out.
13. Performing the procedure for removing the pistons from the connecting rods (in case such a need arises) should also be entrusted to car service specialists. In parallel, connecting rods can be checked for signs of bending, twisting and other deformations using special diagnostic equipment.
Note. Unless necessary, pistons should not be removed from the connecting rods.
14. Check up rods on existence of cracks and other mechanical damages. Temporarily remove the lower head covers, remove the old bearing shells, wipe the beds in the covers and heads and check them for burrs, scuffs and roughness. When finished checking, put the liners in place, install the caps on the lower connecting rod heads, and finger-tighten the mounting bolts.
Note. If the engine is being repaired to eliminate finger knocking, replace the connecting rod assemblies.