Note: Use new rings for assembly.
2. When dismantling the rings, be careful not to damage the piston surfaces.
3. Free the piston head from carbon deposits. To do this, you can use a brush or fine sandpaper. Never use a power wire brush: the piston material is very soft and easily damaged.
4. Clean the piston grooves from carbon deposits with a special tool or ring fragments. Remove only carbon deposits without damaging the groove surfaces.
Pic. 17.4 Piston grooves can be cleaned with a piece of old ring
5. Wash the piston/connecting rod assembly and dry it. Make sure the drain holes in the oil ring groove are free of deposits.
6. If the block has not been bored, the pistons are not needed, but the rings must be replaced anyway.
7. Inspect the piston for cracks around the skirt, pin bosses, and interrings.
8. There should be no risks and scuffs on the skirt, holes in the head and burnout of the piston edges. If there are signs of scuffing on the skirt, the engine has overheated during operation or has abnormal combustion. In this case, carefully inspect the cooling and lubrication systems. Holes in the piston head indicate abnormal combustion ("glow ignition").
Burnout of the edges of the piston head indicates detonation combustion. This should be kept in mind when starting a repaired engine and correcting the carburetor, ignition, EGR, air leakage past the carburetor.
9. Small spots of piston corrosion indicate coolant leakage into the combustion chamber and/or crankcase. Eliminate leaks during assembly.
10. Measure the backlash between the new piston ring and groove. Take measurements in three or four places around the circumference. If the clearance is more than acceptable, replace the pistons.
Pic. 17.10 Measure the backlash between the ring and the groove at several points along the circumference
11. Measure the piston diameter and calculate the clearance in the piston-cylinder pair (see section 15). Piston measurements are carried out along the skirt in two planes, parallel and perpendicular to the axis of the finger and spaced 16 mm from the bottom of the skirt. If the gap is greater than the allowable, then the block requires boring to the next repair size, with the corresponding replacement of the piston and rings.
Pic. 17.11 The piston diameter is measured in a plane perpendicular to the axis of the piston ring and at a distance of 16 mm from the skirt cut
12. Check up a backlash in a joint the piston/pin/rod by twisting of the piston and a rod in opposite directions. Excessive mutual movement indicates the need to replace the node.
13. It is not recommended to carry out work on disassembling the piston / connecting rod assembly and restoring its performance on your own.
14. Check up a rod on existence of cracks and other damages. Remove the connecting rod cap and remove the bushings. Make sure that there are no scratches, abrasions or dents on the landings of the liners. Assemble the connecting rod, tightening the nuts by hand.
Note: If the engine was stalled by the sound of a pin or connecting rod bearing, replace the connecting rod.