Caution! Old piston rings must always be replaced when disassembling the engine.
1. Carefully remove the rings from the piston using a special tool.
2. When removing the rings, be careful not to damage the piston surfaces. If a special tool is not available, the rings can be removed using old feeler gauges or equivalent narrow metal strips. Carefully spread the ring, insert the plates between the ring and the piston, remove the ring by sliding it along the plates.
3. Repeat the operation with the remaining rings, making sure not to allow the bottom ring to enter the groove above. Since rings are subject to mandatory replacement, their accidental breakage should not be ignored, but the experience gained when removing rings will be very useful when installing new rings on the piston.
4. Scrape off any carbon deposits from the bottom of the pistons. After removing the top rough layer of carbon, clean the piston crown with a brush or sandpaper on a cloth backing. Never attempt to remove any remaining carbon deposits with a wire brush attached to a power drill, as this may erode the soft alloy from which the pistons are cast.
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5. Using a special tool, remove carbon deposits from the piston ring grooves. If such a device is not available, you can use an old broken piston ring. Remove only the carbon deposits, being careful not to remove any piston material. Be careful not to damage the ring groove seating surfaces. Be careful not to cut yourself, as the edges of the broken ring are sharp.
6. After removing the carbon deposits, thoroughly rinse the ring groove surfaces with solvent and dry thoroughly. Make sure the oil drain grooves where the oil scraper ring is installed are clean.
7. If there are no signs of significant wear and if cylinder boring is not required, then the pistons should not be replaced. Normal wear is evident as traces of uniform vertical wear on the piston's friction surface and as a slight loosening of the upper compression ring's fit. Replacement of piston rings is mandatory.
8. Carefully check for cracks in the piston skirt, piston pin bosses and piston ring seats.
9. Check for chips and burrs on the friction surface of the piston skirt, traces of burnout in the central part of the piston crown, and burnout on its crown. If chips and scuffs are observed, this indicates frequent engine overheating, one of the causes of which may be abnormal combustion of the fuel mixture. In this case, a thorough check of the lubrication and cooling systems is required.
10. Burnout at the bottom of the piston indicates that the engine is running with incorrect ignition timing. Piston crown burns are usually caused by abnormal combustion (detonation). If these defects are detected, their cause must be identified and corrected; otherwise, serious damage may occur.
11. Piston corrosion in the form of pits indicates penetration into the combustion chamber (and also in the crankcase) coolant. Here again, it is necessary to find their cause and eliminate it, otherwise the repaired engine may fail.
12. Measure the gap between the ring groove area and the piston ring by inserting a new ring into the groove and passing a feeler gauge between the groove and the ring. Check the clearance in three or four places along the entire length of the groove.
13. Make sure this ring fits the groove it will be installed in, as different grooves vary in size. If the clearance exceeds the established limit, the piston should be replaced.
[Based on website data: MazBook]
14. Check the clearance between the piston and cylinder by measuring the corresponding diameters. Make sure that measurements are taken on a pair of mating parts.
15. Measure the piston skirt diameter. The clearance value is determined as the difference between the diameters of the cylinder and the piston skirt. If the clearance exceeds the established limit, the cylinder block must be bored, and the pistons and rings must be replaced with repair ones. (The clearance between the piston and the cylinder can also be measured, but with less accuracy, using a feeler gauge placed between the piston inserted into the cylinder and the cylinder).
16. Check the clearance between the piston pin and the connecting rod head by rocking the piston and connecting rod in opposite directions. A noticeable amount of play will indicate an increased gap and the need to repair this connection. The piston assembly with the connecting rod must be submitted for repair to replace the piston pins, as well as to bore the connecting rod head and the piston hole to the repair dimensions.
17. If you need to remove the pistons from the connecting rods to replace the pistons or to eliminate piston pin play, you should take them to an auto service workshop. At the same time, it will be necessary to check the bending and twisting of the connecting rods, for which the workshops have the necessary equipment. If new pistons or connecting rods need to be installed, the pistons should not be disconnected from the connecting rods.
18. Check the connecting rods for cracks or other damage. At this stage, remove the connecting rod bearing caps, take out the bearings, wipe the bearing seating surfaces on the connecting rod cap and on the connecting rod, and check for cracks, scratches and burrs. After checking, reassemble the connecting rod, installing the bearings in place, and tighten the nuts by hand.