2. Remove carbon deposits from the piston ring grooves (photo).
15.2a Clean the piston grooves using the tool...
15.2b... or an old piston ring
3. Wash the pistons and connecting rods with solvent, carefully clean the drainage holes in the piston grooves and the hole in the connecting rod (photo).
15.3 Oil drain hole in connecting rod
4. If there are no signs of significant wear and if cylinder boring is not required, then the pistons should not be changed. Normal wear shows up in the form of traces of uniform vertical wear on the rubbing surface of the piston and in the form of a slight weakening of the fit of the upper compression ring. However, the replacement of piston rings during engine overhaul is mandatory.
5. Carefully check up presence of cracks on a skirt of the piston, on bosses of a piston pin and on landing platforms of piston rings.
6. If chips and scuffs are observed on the piston, then this indicates frequent overheating of the engine. In this case, a thorough check of the lubrication and cooling systems is required. Burning in the bottom of the piston indicates the operation of the engine with an incorrect setting of the ignition timing. The cause of burning of the piston crown at the edges is usually abnormal combustion (detonation). If these defects are found, then their cause must be found and eliminated.
7. Piston corrosion in the form of small pits (pitting) indicates penetration into the combustion chamber (as well as in the crankcase) coolant.
8. Measure the gap between the groove and the new ring (photo). If the clearance exceeds the specified limit, the piston should be replaced.
15.8 Measuring the gap between the groove and the new ring
9. Check the clearance between the piston and the cylinder by measuring the diameter of the cylinder (see above) and the piston diameter of the given cylinder (photo). If the gap exceeds the established limit, then the cylinder block must be bored, and the pistons and rings should be replaced with repair ones.
15.9 Measuring the piston diameter. Diameter measured perpendicular to the axis of the finger 1.20.3 mm
10. Check up a backlash between a piston finger and a rod head for what shake the piston and a rod in opposite directions. If the play is noticeable, then the finger hole must be unrolled and a new finger installed.
11. Repair of pistons and connecting rods is carried out in a car service.
12. Check up existence on rods of cracks and other damages. Remove the connecting rod bearing caps, remove the bearings, wipe the seating surfaces on the cap and on the connecting rod, check for cracks, scratches and burrs. After checking, assemble the connecting rod, installing the bearings in place, tighten the nuts by hand.