Note: Always replace piston rings whenever the engine is overhauled.
2. To remove piston tracks, you can use a tool specially designed for this purpose. When removing the rings, be careful not to scratch the piston.
3. Scrape off any carbon deposits from the piston crown. To complete this operation, you can use a hand-held wire brush or fine sandpaper. Do not, under any circumstances, use a brush inserted into a drill on this chain. The piston is made of a soft material and such a brush can significantly damage it.
4. Clean the grooves under the ring with a special tool (figure 18.4,a) or a fragment of an old ring (figure 18.4,b). Be careful to remove only carbon deposits from the grooves, not piston metal.
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5. After removing the carbon deposits, wash the pistons and connecting rods with solvent and dry them, if possible, with compressed air. Don't forget to clean the oil holes in the piston grooves and in the connecting rods.
6. If traces of uniform, slight wear are observed on the more heavily loaded tank surface of the piston, and the compression ring in the upper groove has a slight play, this condition of the piston is considered normal and there is no need to replace the piston (if the cylinder has not been bored). However, the piston rings should be replaced in any case.
7. Carefully inspect each piston for cracks in the skirt, bosses and between the grooves.
8. Inspect the piston walls for scuffs and deep scratches, and the bottom for burns and scorch marks. If there are scuffs on the piston skirt, this may be the result of engine overheating due to a faulty cooling system or a violation of the composition of the working mixture. Check the cooling and lubrication systems. Burnout of the piston crown is usually a result of incorrect ignition timing. Bottom burns usually occur during detonation. If defects of this kind are discovered during inspection, the causes that caused them must be eliminated, otherwise they will recur. The causes may be intake manifold leaks, incorrect mixture composition, incorrect ignition timing, or malfunctions in the exhaust gas recirculation system.
9. Piston corrosion, manifested as fine pitting, may be the result of coolant leaks into the combustion chamber or crankcase. In this case, the cause must also be eliminated. otherwise the defect will appear again.
10. Measure the gaps between the rings and the groove walls. To do this, insert the ring into the groove from the side and use a flat feeler gauge (figure 18.10). Check the clearance in three or four places in the groove. Don't mix up the rings - they have different thicknesses. If the gap exceeds the permissible level specified in Technical data, the piston should be replaced.
11. Check the clearances between the pistons and cylinders. To do this, measure the inner diameters of the cylinders (see paragraph 16) and the outer diameters of the pistons. Measure the piston diameter on the skirt in a direction perpendicular to the axis of the piston pin (figure 18.11). Calculate the clearance as the difference between the diameters of the cylinder and piston. If the clearance exceeds the permissible value, it is necessary to ream the cylinders and use pistons of the next repair size.
12. Check the clearance in the connection between the upper connecting rod head and the pin. trying to swing the connecting rod relative to the pin. Noticeable play indicates increased wear that should be eliminated.
13. If for some reason it is necessary to separate the connecting rods from the pistons, it is better to do this at a service station or workshop. There you can also check whether there are any deviations in the shape of the connecting rods.
14. Measure the length of the connecting rod lower head bolts from the bottom surface of the head to the end of the thread. On 4-cylinder engines, the bolt length should not exceed 46 mm, and on V-engines, 48 mm. If the bolt length exceeds these values, it means the bolts have stretched during operation and should be replaced. If even one bolt is found to be defective, replace the entire bolt set.
15. Inspect the connecting rods for cracks and other defects. Temporarily remove the lower head covers, remove the old bearings, wipe the bearing surfaces with a clean cloth and inspect them for dents, cracks or burrs. After inspection, reinsert the old liners, install the covers and tighten the mounting nuts by hand.