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The best method for fitting rings to cylinder bores is by squaring the ring approximately
No matter how much we love them, our engines are still basically inefficient air pumps and need all the help they can get to make power. Like any other type of pump, if it leaks, it won't work. And since it's the pistons that are doin' the pumpin', if they're allowed to flop around in the bores, they'll leak and little power would be the result. Not only would power suck, the pistons, along with the rest of the engine would quickly destroy itself.
Your rings may look like ordinary bands of steel, but they are far from simple in their design and construction. They work to locate the pistons in the bores while sealing the cylinders for power and directing oil to the proper spots to keep the engine alive. Ring thickness, tension, shape, material, and profile all play a crucial role in cylinder sealing, power making, and oil control.
The Fire RingThe top ring's main job is sealing the combustion process and many refer to it as the "fire" ring. The top ring works in a dual capacity by holding high vacuum as the piston moves down its bore and by keeping cylinder pressures high when the combustion process begins. Ring gap is critical and, if left uncontrolled, much of the combustion gasses would simply escape into the crankcase. Anytime you allow cylinder pressure past the rings, (otherwise known as "blow by"), you are losing horsepower.
This cut-away clearly shows the gapless top ring's twin overlapping ring design.
Utilizing a two-piece, overlapping ring design with their gaps placed 180 degrees apart; gapless rings are engineered to eliminate as much blow by as possible. Obviously, a small amount of combustion gasses will always leak past the top ring, but that is helpful in creating the proper seal for the second ring. Performance top rings will usually be marked to identify which side faces up in the bore. That's because the inner diameter of the top ring is tapered to force the rings out and increase the seal against the cylinder walls as the piston goes up the bore. If installed upside-down, the top ring will lose power.
The Second RingThe second ring serves as a back up to the top ring in sealing the crankcase from the combustion process. But, more importantly, it acts as an oil scraper to keep any oil that has migrated past the oil control rings from seeping into the combustion chamber. The second ring usually features a smaller gap than the top ring, due to the lower amount of heat and correspondingly less expansion it will see. In almost every case, cast iron is the material of choice for the second ring and it will typically not have a face coating.
The fact that the top ring absorbs the majority of combustion abuse allows a cast iron ring to be used in the second groove of almost any engine. Second rings are designed several ways; with the reverse-torsional taper face being the most common. The taper face allows the ring to ride over the film of oil on the upstroke and scrape oil off the cylinder walls on its way down. The other basic second ring design is the wiper ring that has a groove cut on its bottom face to wipe oil down.
The most affordable compromise between cost and efficiency when filing rings is still a ha
The Oil RingThe last ring set is just as important as the rest, yet often ignored. The oil rings are critical to maintaining engine life, as well as controlling detonation. Oil rings are very thin chrome-faced stainless steel bands with stainless steel expanders in between. Oil rings do not need to be gapped, but their fit should be checked prior to installation to make sure the ends don't butt together. Both standard and low-tension oil rings are available. However, low-tension oil rings should only be used in engines equipped with an external vacuum pump. Otherwise, excess oil may seep into the combustion chambers where it could ignite and cause detonation.
Performance RingsOriginal equipment engines are usually equipped with uncoated cast-iron rings and considering how long most factory engines last, many good things can be said for their durability. The cast-iron ring's biggest advantage over other sets is its low cost and wide availability. Another advantage is that a cast ring is very easy on cylinder walls and has great wear characteristics. The main disadvantage to a cast-iron ring is that it may break if subjected to the rigors of high-compression and/or detonation. Cast-iron rings can safely be used in the top groove of engines up to 11:1 compression.