April '17

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APRIL 2017 PRECISION ENGINE 11 PRECISION ENGINE wheel, a flat base and a crank handle. Place the ring flat on the base, with one end of the ring contacting the left side of the wheel. Always keep the end of the ring squared to the wheel to avoid creating a tapered/ angled cut. While maintaining pressure of the ring to the wheel, turn the handle counterclockwise (toward you). Count your strokes as you file, and always file in a direction from the inside of the ring toward the outside of the ring—don't reciprocate the file back and forth. After every few filings (let's say every five), flip the ring over and file the opposite end by the same number of strokes. Clean the metal debris from the ring, place it back into its assigned cylinder and measure the gap again. You'll need to repeat the pro- cess a number of times until you obtain the desired gap. Also keep in mind that material removal will likely occur sooner with second rings due to the likelihood of softer material. After completing a few rings, you'll get a feel for how many file strokes are needed. Remember to take your time: you can always file more, but you can't add mate- rial if you file too much. Once you're satisfied with the ring gap, carefully deburr the gap edges using a fine file, then wash all rings to remove any particles. Keep all rings organized per cylinder locations. In addition to checking ring gap with each ring in its respective cylinder bore, you should also check how the rings fit in your pistons. When checking ring radial back clearance for top and second rings, with the ring set in its groove and side clearance (ring face radius pro- truding out) at 0.001 to 0.002 inches, radial back clearance should be at least 0.005 inches. INSTALLING THE RINGS Once the rods are assembled to the pistons, install the oil ring support rail (if your pistons require these support rails), making sure to place the rail's small male dimple facing down, and positioned over the pin bore void. The oil ring package is then installed (expander ring, followed by the lower oil ring rail followed by the upper oil ring rail), followed by the second and top rings. Pay attention to the expander ring, making sure that the ends remain butted and do not overlap. Ring makers provide a reference mark to indicate which side of the ring must face upward. Usually, top and second rings feature a small dimple dot. If you see a dot, the dot must face upward when installed. High-performance engine building often requires using file- to-fit piston rings. The top and second rings will feature a very tight gap or even overlapping ends. This extra material allows you to custom-fit each ring in order to achieve the required ring end gap for a specific bore diameter.

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