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ADDING SIDE VALVE-SCREW HOLES
MARK HOLE LOCATIONS: Wrap two pieces of masking tape perfectly straight around the diameter of the tube at both edges of the bottom hole. Measure to mark the exact center between the tape strips on both sides of the tube. Use a scribe, center punch or similar sharp object to precisely mark the center, the more perfect your marks and measurements are the better the holes will line up in the end. Remove those tape strips. Wrap one perfectly straight around the tube with one edge at the center-lines you marked on the sides. Use a razor blade to cut the tape in the middle of where the two ends overlap. Remove the trimmed piece of tape that is now the exact length of the tube diameter. Place it on a clean-smooth surface, sticky-side down. Mark the exact middle of the tape length near the edge that will be your center-line. That is where the port-hole center will line-up. The loose ends will meet-up in the center of the bottom hole. The half-way point between the port center and loose ends will be the side hole locations. Place the tape back on the tube lined up with your center-line marks and mark the hole locations.
DRILL HOLES: Use a center punch or scratch awl to dimple the tube at the exact center of each hole. This helps prevent the bit from wandering. Use sharp bits, cobalt works better, slow rpm to avoid chatter and cutting or motor oil to help the bits cut clean and stay cool. Start with a small bit, this will stay on center better, then step up to larger sizes. For final sizing you can use a reaming tool or the precise drill bit size. For 22XX the hole is .281 or 9/32". The hole edges inside the tube need to be deburred and cleaned-up after, the valve may not fit if there's any burrs.
Do not use a lot of force on the tube when dimpling the hole centers or drilling. This can indent the tube and cause the valve not to fit after. The Magnum Valves are larger diameter than standard valves so this is more critical for those.