Withdrawal
1. See Section 1A, and remove the cylinder head, flywheel, sump and baffle, oil pump and its intake tube.
2. If a ridge formed by carbon deposits or wear is visible on the top of any of the cylinders, remove it with a scraper or reamer, respectively, to avoid damaging the piston during removal.
3. Using feeler gauges, measure the clearance between the connecting rods and the bearing surface of the crankshaft counterweight and record the results.
4. Rotate the crankshaft so that piston No. 1 is at bottom dead center. If not numbered by the manufacturer, use a hammer and punch or paint to mark the cylinder number on each connecting rod bearing cap and on the connecting rod itself (see illustration). Mark the orientation of the bearing caps relative to the connecting rod to ensure correct assembly.
5. Loosen the bearing cap nuts/bolts by turning them half a turn at a time and remove the cap (see illustrations). Remove the lower bearing shell from the shaft and tape it to the cover so that it does not get lost. Note that if the bushings do not require replacement, they must be installed on the same connecting rod.
6. Where the bearing caps are nutted, wrap the threaded ends of the studs with masking tape to prevent them from scratching the crankshaft journals and cylinders when removing the pistons (see illustration).
7. Remove the piston from the cylinder up by pushing it with the hammer handle. Remove the upper bearing shell and tape it to the connecting rod for safety (see illustration). On engines equipped with piston oil jets (installed at the bottom of the cylinders), make sure that when removing the piston, the connecting rod does not damage the jet.
8. On 5-cylinder engines, turn the crankshaft to bring piston #2 to bottom dead center, then remove the piston. Remove pistons #4, #5, and #3 in the same way. Store components from the same cylinder together to avoid mixing them up during installation (see illustration).
9. Where present, remove the mounting screws and remove the piston cooling oil jets from the base of the cylinders (see illustrations).
Inspection
10. Insert a small flathead screwdriver into the existing groove and pry out the piston pin circlips. Push out the piston pin and separate the piston from the connecting rod (see illustrations). Discard retaining rings - they must be replaced. If the pin cannot be removed, heat the plunger to 60°C with hot water.
11. Before starting the inspection of the pistons, it is necessary to remove the piston rings from them using a special tool or an old feeler gauge. Remove the top piston rings first by gently prying them apart. Be careful not to scratch the piston with the ends of the ring. Rings are brittle and will break if unclenched too much. In addition, they are very sharp - protect your hands with gloves. Throw away the rings, they need to be replaced (see illustration).
12. Remove carbon deposits from the piston ring grooves using a piece of the old ring (break the ring in half, being careful not to cut your fingers). Be careful not to remove metal along with soot and do not scratch the walls of the grooves.
13. Clean off the main deposit from the piston head (see illustration). Then clean it with a wire brush or fine sandpaper. Be careful not to scratch the piston.
14. After removing carbon deposits, clean pistons and connecting rods with kerosene or a suitable solvent and dry them thoroughly. Make sure the oil return holes in the annular grooves are not clogged.
15. Inspect the pistons for damage and signs of excessive wear. Normal wear of the piston is manifested in uniform vertical wear of the surfaces of its axial pressure and a small play of the upper ring in the groove. If you find signs of wear other than those indicated, check whether the component is suitable for further use and what is the reason for the wear.
16. A worn or scratched piston skirt may indicate that the engine has been overheating due to inadequate cooling or lubrication. Burned-out areas on the piston walls indicate that gas breakthrough has occurred, possibly caused by wear on the cylinder walls or piston rings. Dimples or burnt areas on the piston crown usually indicate that the engine is pre-igniting or knocking. In particularly severe cases, the piston head may even melt. Pitting of the piston crown indicates that coolant has leaked into the combustion chamber. If any of the above damage is found, identify the causes and eliminate them, otherwise the damage will occur again.
17. Check pistons, connecting rods, piston pins and bearing caps for cracks. Lay the connecting rods on a flat surface and visually inspect them for deformation. If in any doubt, have a specialist take accurate measurements using appropriate instruments. Inspect the connecting rod bearing for cracks and signs of wear.
18. Using a micrometer, measure the diameter of all four pistons 10 mm from the base of the skirt along an axis perpendicular to the axis of the piston pin (see illustration). Compare the measurement results with the data given in Specifications. If the piston diameter is out of tolerance, replace the piston.
Note: If the cylinder block was bored out during a previous overhaul, oversize pistons may have been installed. Record the results of all measurements, after measuring the diameter of the cylinders, it will be possible to determine the piston clearances from them (see later in this Section).
19. Install a new piston ring in the corresponding groove and measure the gap between the ring and the groove wall using a feeler gauge (see illustration). Please note that the rings have different widths, do not mix up the grooves. Compare the measurement results with the data given in Specifications. If the clearance is out of tolerance, replace the piston.
20. Inspect the connecting rod bearing and piston pin for damage and signs of wear. If the wear is excessive, the piston pin must be replaced and a new bushing installed in the connecting rod. This work should be entrusted to a specialist.
21. Connect the piston to the connecting rod, observing their correct relative position. An arrow is marked on the piston head (may be tarnished) (see illustration), which should be directed towards the front end of the engine. The connecting rod and bearing cap have indentations located near their contact surfaces, which should face the same direction as the arrow on the piston head (see illustration).
7.21b Piston assembly
1 — Piston rings
2 - Piston
3 - Piston pin
4 - Retaining ring
5 - Connecting rod
6 - Insert connecting rod bearing
7 — the Top part of the block of cylinders
8 - Connecting rod bearing cap
9 - Mounting pin (not on all models)
10 - Oil jet for cooling the piston (not on all models)
11 — the Screw of fastening of an oil jet
12 - Bolts of the connecting rod bearing cap
A - Identification marks of the bearing cap / connecting rod
B - Approximate marks of components
Note: On some engines, the connecting rod ends have dowel pins that fit into holes in the bearing caps. The pins must be installed in the connecting rods, not in the caps.
22. Lubricate the piston pin and connecting rod bushing with clean engine oil. Push your finger into the piston through the top end of the connecting rod. Install two new circlips on both ends of the piston pin. Repeat this step for the remaining pistons.
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