Inspection
1. Before starting inspection, the piston/rod assemblies must be cleaned and the piston rings removed from them.
2. Gently spread the rings and remove them from the piston crown. Use two or three old feeler gauges to keep rings from slipping into already empty grooves (refer to accompanying illustration). Please note that the oil scraper ring consists of two parts.
3. Clean off the main deposits from the piston bottom. Then clean it with a wire brush or fine sandpaper.
4. Remove carbon deposits from the piston ring grooves using a piece of the old ring (break the old 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.
5. After removing carbon deposits, clean the piston/connecting rod assembly with kerosene or a suitable solvent and dry it thoroughly. Make sure the oil return holes in the annular grooves are not clogged.
6. If the pistons and cylinder walls are not damaged or worn, and if the cylinder block does not need regrinding, you can install the old pistons. Normal wear of the piston is manifested in the uniform vertical wear of the surfaces of its axial pressure and a small play of the upper ring in the groove. When assembling the engine, the piston rings must be replaced.
7. Carefully inspect each piston for cracks in the skirt, around the piston pin holes, and between the ring grooves.
8. Inspect the piston skirt for damage and the piston crown for holes and burnt edges. If the skirt is scratched or nicked, or there are pits or burn marks on the piston crown, the engine may have overheated and/or misfired (incorrectly adjusted fuel mixture ratio or injection/ignition timing). Carefully check the cooling and lubrication systems. Burnt areas on the sides of the pistons indicate that a gas breakthrough has occurred. If any of the above damage is found, identify the causes and eliminate them, otherwise the damage will occur again. On gasoline engines, the cause may be an intake air leak, improper fuel/air mixture adjustment, or incorrect ignition timing. On diesel engines - the wrong moment of injection of the fuel pump or a defective nozzle.
9. Piston corrosion indicates that coolant has leaked into the combustion chamber and/or crankcase. Find the cause of the leak and fix it.
10. If new rings are installed on old pistons, measure the gap between the ring and the groove wall by inserting a new ring into the groove and measuring the gap with a feeler gauge. Check clearance in three or four places around each groove. No specific data is specified by the manufacturer, but if the measured clearance is greater than 0.10 mm, new pistons will be required. If the new ring is too tight in the groove, it is most likely due to dirt remaining in the groove.
11a. Check clearance between pistons and cylinder/liner walls by measuring the inner diameter of the liner or cylinder (refer to section Removal and installation of an intermediate shaft) and piston diameter. Measure the piston diameter on the skirt perpendicular to the piston pin (refer to illustrations). Subtract the piston diameter from the cylinder/liner diameter to get the clearance. If it is more than the data given in the Specifications, the cylinder block must be bored and new pistons and rings installed. On E7J engines, new pistons and liners are supplied in matched pairs.
11b. The diameter mark is marked on the piston crown.
12a. Check the installation of the piston pin by turning the piston and connecting rod in opposite directions. If there is play, this indicates excessive wear and the pistons and connecting rods must be separated (K7M and E7J engines). This should be entrusted to a Renault workshop or an engine overhaul specialist.
12b. Note that on diesel engines and gasoline engines F3R and F7R, the piston pins are secured with locking rings. Note the location of the piston relative to the connecting rod (refer to illustrations).
13a. Before installing the ring on the piston, check the clearances of the cuts (refer to illustrations).
13b. No data has been specified by the manufacturer, but the following values can be used approximately: 0.50 mm for compression rings and a little more for oil scraper rings. In Renault rings, the gap cannot be adjusted.
Assembly
1a. Install new piston rings (refer to illustrations).
1b. Note that the second compression ring is tapered. Both compression rings must be installed so that the word "TOR" was turned up.
1c. Space the gaps of the ring cuts evenly 120°apart.
1 - Top compression ring;
2 - Lower compression ring;
3 - Oil scraper ring.
2. Note that on E7J engines, if new piston/liner assemblies are received, each piston is matched to the correct liner and they should not be interchanged.