Piston Ring Tips
| Piston rings will rotate in the cylinder when
the ring side clearance to the ring land is excessive. A new ring in a new groove has 1 1/2 thousandths of clearance built into the ring. Once the piston grooves wear the ring is not held properly and will rotate. In a horizontal engine the force of gravity will work the gaps to the top. With proper clearances this will not happen. If you see all the gaps lined up you had better check for ring groove wear because trouble is just over the horizon. The greatest old wives tale about piston rings is that there is great importance to the gap whether in size or orientation. The gap is only about 5 percent of the equation that includes the ring side clearance. When there is compression leakage past a ring 95% goes past the sides of the rings and never enters the gap. If you bother to check the end gap why don't you check the most important thing - the fit of the ring to the groove? Most people don't. Then when they don't get any compression they call me. You can live with as much as 5 thousandths of side clearance but 6 or more means you will not be happy with your results. Machine work will be needed. Pins in the grooves will force a ring to seat in one spot but there again when the ring grooves wear the seal will fail. Gap size should be a minimum of 3 thou per inch of bore for easy break ins. Engines that will work hard and hot immediately after overhaul need 4 thou minimum end gap per inch of bore. As much as 8 thou per inch of bore is acceptable.
The other thing people overdo
is hone. They want to see a
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