Note. Always use new piston rings when reassembling the engine.
2. Using a piston ring installer, carefully remove the rings from the pistons. Be careful not to scratch the pistons.
3. Clean off all traces of carbon deposits from the top of the piston. Most of the carbon deposits can be removed with a hand brush or a piece of fine-grained sandpaper. Under no circumstances should you use a wire brush mounted on a drill to remove carbon deposits. The piston material is soft and easy to remove with a brush.
4. Use a piston ring groove cleaner to remove carbon deposits from the grooves. If you do not have such a tool, a piece of an old ring will do. Be careful - only remove carbon deposits, but do not remove metal from the surface and do not scratch the walls of the grooves under the rings (see illustrations).
18.4a. The piston ring grooves must be cleaned with a special tool, as shown in the illustration... | 18.4b....or a piece of a broken ring |
5. After removing deposits, clean the pistons with connecting rods and dry them with compressed air (if it exists).
Attention! Wear safety goggles. Make sure the oil drain holes on the back of the ring grooves are clean.
6. If the pistons and cylinder walls are not damaged or excessively worn, and if the block cylinders have not been bored, then new pistons are not needed. Normal piston wear manifests itself as uniform vertical wear of its thrust surfaces and a small clearance of the upper ring in its groove. However, when overhauling an engine, it is always necessary to use new piston rings.
7. Carefully check each piston for cracks around the skirt, near the bulges under the finger and in the areas of the rings.
8. Check for scratches and abrasion marks on the thrust surfaces of the skirt, holes in the piston head, and burnout areas on the edge of the head. The presence of scratches or abrasions on the skirt means that the engine may have overheated and/or is not combustion properly, resulting in abnormally high operating temperatures. The lubrication and cooling systems must be carefully checked. The presence of a hole in the bottom of the piston indicates improper combustion of the mixture (early ignition). Areas of burnout on the edge of the piston head are usually the result of detonation. If these problems do occur, their causes must be eliminated, otherwise further damage is inevitable. These reasons may be: air leakage, improper air-fuel mixture, use of fuel with a low octane rating, malfunction of the ignition system and the EGR system (exhaust gas recirculation).
9. Piston corrosion shaped small "sores" indicates a coolant leak into the combustion chamber and/or crankcase. This fault must be repaired immediately, as similar problems can occur with a rebuilt engine.
10. Measure the backlash of the piston rings by installing a new ring in each groove and inserting a feeler gauge behind it into the groove (see illustration). Check clearance at three or four places around the circumference of the groove. Make sure that the appropriate rings are installed in the grooves (they are different). If the backlash exceeds the value given in this chapter, the pistons must be replaced with new ones.
18.10. Check the ring backlash with a feeler gauge at several points around the circumference of the groove
11. Check the piston clearance in the cylinder by measuring the diameters of the cylinder liners (see section 16) and pistons. Make sure pistons and cylinders match. Measure the piston across the skirt at a 90°angle to the piston pin (see illustration). To obtain an accurate result, the measurement must be carried out at a specific location, which depends on the type of engine.
- A) Piston diameter for engines with a displacement of 3.8 liters (with balance shaft) measured directly at the center line of the piston pin.
- b) Pistons for engines with a displacement of 3.1 liters are measured at a distance of 5/8 inches (15 mm) from the bottom edge of the skirt.
18.11. Measure the piston diameter at a 90°angle to the piston pin and also in line with the pin
12. To obtain the clearance value, the piston diameter is subtracted from the diameter of the cylinder barrel. If the gap exceeds the prescribed value, it is required to bore the cylinders of the block and install new pistons and rings.
13. Check up a backlash between the piston and a rod, twisting the piston and a rod in opposite directions. Any noticeable play indicates excessive wear and must be corrected. Pistons complete with connecting rods should be taken to a car repair shop, where the required dimensions will be restored and new pins installed.
14. If, for any reason, the pistons must be removed from the connecting rods, they must be taken to an auto repair shop. In the workshop, check the connecting rods for bending and twisting, since they have special equipment for this purpose.
Note. Unless new pistons and/or connecting rods are required, do not disassemble pistons with connecting rods.
15. Check up, whether there are no scratches or other damages on rods. Temporarily remove the connecting rod caps, remove the old bearing shells, wipe the connecting rod and cap contact surfaces clean and check for scratches, nicks, and abrasion marks. After checking the connecting rods, replace the old bearings, replace the caps and tighten the nuts by hand.
Note. If an engine overhaul is due to connecting rod knocking, be sure to install new connecting rods.