We used the ProForm filing-tool...
We used the ProForm filing-tool for our 440's rings. The tool is first setup to square the rings of the bore size to the abrasive wheel by adjusting the eccentric locator. The ring is only square at one distance from the abrasive wheel, so we set the slide .100 inch from the stop, and then adjusted the eccentric with the ring end just touching.
Ring Tricks and Trick Rings
Conventional rings do a good job, but in any kind of competitive environment, there will always be those looking for something to gain a competitive edge. There are many unconventional ring systems and designs available, and, as with anything different, there will be detractors and advocates. Gapless rings seek to effectively close the endgap of a ring completely to gas flow, with the goal of achieving a bare minimum of pressure loss through the end gap. Two manufactures have had success in this marketplace, with substantially different approaches to closing the endgap. Total Seal rings are actually a two-piece design, in which the main ring carries a secondary rail. By staggering the gaps in these two portions of the ring, the gap is effectively closed. Childs and Albert produces their ZGS ring with each end of the gap formed with a fitted step, which when installed overlap at the endgap also effectively closes the path to gas flow. Both of these ring designs can be installed in conventionally designed ring lands, and can be employed in engines from street to race.
Rings are manufactured to SAE specifications in terms of radial thickness, standardizing the dimension to match correspondingly standardized ring lands in pistons. Decreasing the radial thickness of the ring can be done to alter or reduce a ring's static tension by increasing the ring's inside diameter-a process referred to as back-cutting. A back-cut ring can reduce drag considerably, but the shallower ring should be used in conjunction with a correspondingly shallower custom ring groove to maintain the appropriate ring-back clearance. Custom piston manufacturers routinely accommodate specific ring requirements. As static tension is reduced via ring design, the ring must rely more upon gas loading to effectuate a seal. Low-tension back-cut or .043-inch top rings are often run in conjunction with gas port in the pistons to direct pressure to the ring land area to assist the cylinder seal. The Dykes ring design accomplishes lower tension and gas loading without the necessity of gas ports through its stepped design. All of these ring tricks have been successfully employed in racing applications, although specific combinations are usually up to the engine builder to refine and develop.
Gapping Rings
Ring gaps represent an area of pressure loss in a running engine, and it has been found that a minimal endgap under operating conditions offers a measurable power increase. However, rings expand due to heat retention, and if not enough gap is present, the gap may close entirely while the engine is operating. This condition is referred to as "butting" the endgaps, and the result can be disastrous. Replacement ring sets are sized conservatively for the nominal bore size of the engine, usually with generous endgap clearances to minimize the potential of butting the endgaps. In a serious performance application, custom sizing the endgaps to an exact specification will minimize the pressure loss through the ring endgap, and enhance power. Manufactures offer "file-fit" ring sets, normally speced at .005-inch larger than the nominal bore dimension, providing an oversized ring that can be custom fit to the cylinder bore.
While the potential advantage of file-fit rings is simple to conceptualize, the question becomes what is the correct endgap? The required endgap can vary with the ring material, application, cylinder bore diameter, piston material, and top ring placement. Ring manufactures offer guidelines based upon their finding of what works in various applications. Some piston manufacturers have their specific specs on ring endgap requirements with their product that should supersede the recommendation of the ring manufacturer.
How are the rings actually brought to size? Excess material is removed at one or both ends of the ring, until the gap measures within spec. Trimming the ring gap can be done by a variety of methods. We know engine builders who hand cut the gaps with nothing but a quality draw file. Low-cost, hand-crank, ring filing tools are popular with most casual builders. More elaborate electric grinders with ring fixturing capabilities are also available. Basically, it's cut and measure a little at a time, until the desired dimension is reached.
Here's how we recently did a set of file fit Childs & Albert Dura-Moly rings for our 440.
The ring is then clamped into...
The ring is then clamped into position, and the dial indicator zeroed when the ring is brought into contact with the abrasive wheel. The dial indicator will read how many thousandths have been taken off. Remeasure the ring in the bore to confirm the correct gap has been achieved and the gap is parallel. It's better to stop short on the cutting and make a check than to take too much off the ring, particularly on the first few rings until the setup is confirmed.
The hand-crank wheel is a...
The hand-crank wheel is a lower cost alternative, but requires repeated trial-and-error test fitting and measuring for the desired fit. Some builders will file from only one side to manually align the squareness of the cut. Always cut with the wheel turning inward towards the center of the ring, as an outward cut will flake the moly from the ring face around the gap. My favored technique to control the parallelism is to press the ring firmly into the stop pins if more material needs removal from the outside of the gap. Alternatively, to take more from the inside of the gap, the ring is pressed lightly against the stop pins and squeezed more tightly in the center. You have to develop the feel.
After filing, the ring will...
After filing, the ring will have a raised burr at the cut edge. This will cause the ring to hang-up in the groove and can also damage the piston. A small, fine needle file can be used to lightly deburr the edge, but don't chamfer it. We used this deburring tool from Childs & Albert, which worked nicely.