Another sign of piston wear is piston knocking, similar to crankshaft noise, which must be distinguished from bearing knocking. It can be clearly heard at low engine speeds when there is no load (e.g., in idle mode), and is much less audible as engine speed increases. Piston wear usually occurs in the area of the skirt or lower end of the piston. It is also noticeable where the skirt thickness differs from normal.
To check the wear of the piston rings, remove the rings from the piston, insert the rings into the cylinders from above, pushing them down approximately 40 mm using the piston (from which the rings were removed). Then measure the gap in the ring joints using a feeler gauge. If the gap exceeds the specified maximum, the rings need to be replaced.
Over time, the grooves in which the rings are located on the piston can also increase in size. The gap between the ring and the piston in the groove should not exceed 0.102 mm for the two upper sealing rings and 0.076 mm for the lower oil scraper ring.
However, it is rare for a piston to be worn only in the ring grooves, and replacement is unlikely to be necessary for this reason alone. Whenever pistons are replaced, the weight of the four sets of pistons and connecting rods must be within 8 grams of change to maintain overall engine balance.
1. To remove the piston rings, carefully slide them towards the top of the piston so as not to scratch the aluminum alloy; never move them towards the piston skirt.
Caution! Piston rings can be easily damaged if removed carelessly, so this operation must be performed with extreme caution. You can use old feeler gauges.
2. Lift one edge of the piston ring that needs to be removed from the groove and insert a feeler gauge under it.
3. Slowly move the feeler gauge around the piston and when the ring comes out of its groove, remove it upwards, with the feeler gauge holding it from slipping into an empty groove, if there is one already.
Caution: Piston rings should always be removed through the top of the piston.
4. Check that the piston ring grooves are clean.
The easiest way to install the rings is to use a feeler gauge and install the rings one at a time, starting with the bottom oil ring. The feeler gauge can then be moved down over the other piston ring grooves until the correct groove is reached. The piston ring is then slid off the feeler gauge into the correct groove.
Another method of inserting rings is to hold them between your thumb and forefinger. This method requires strong hands and great care, as the ring can be opened too much and broken.