Place the face of the new ring in the groove, as shown in Figure 7.12, and roll it around the piston. it should be free in all parts of the groove. If the ring is tight in any spot, the groove should be cleaned and the ring tried again.
The side clearance of the ring in the groove is checked with a feeler gauge (Figure 7.13). This can be done by holding the ring in its groove, or with the ring installed on the piston. Average specifications for side clearance are 0.035 mm for petrol engines and 0.05 mm for diesel engines.
The steel rails and separators of segmental rings are carefully wound into the groove in the piston, one piece at a time, making sure that they are correctly seated (Figure 7.14). The ring can be turned in its groove if it is correctly installed.
Cast iron compression rings can be installed in a similar way, but care must be taken that the
A compression ring with a tapered face or counter-bore must be installed with the correct side of the ring to the top, as shown in Figure 7.15. If a ring is fitted upside down, its action will be reversed. A scraper ring, for example, would carry oil up the cylinder wall into the
When the rings are installed in their grooves, the ring gaps should be staggered so that all the gaps are not in line. The gaps are kept away from the thrust sides of the piston. Figure
Following are related points:
1. Oil the piston and rings and stagger the ring gaps.
2. Fit a piece of plastic tube over the connecting-rod bolts so that they will not scratch the crank-pin journal (Figure 7.18).
5. Insert the piston using light even taps with a hammer handle on the head of the piston. Only light taps will be needed if a good compressor is used and operated correctly. Heavy
6. Hold the compressor firmly against the surface of the cylinder block so that there is no gap for the rings to escape.
New precision connecting-rod bearings are required if the old ones are defective or have worn so much that clearances are excessive. New bearings will also be required if the crankpin journals have worn out-of- round or tapered to the extent that