THE SHOP

April '17

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10 PRECISION ENGINE APRIL 2017 PRECISION ENGINE B efore installing the pistons and con- necting rods, address the piston rings. If you have standard bores, standard replacement rings should be fine, but you should still check ring fit/gap to make sure. Never assume that rings are already sized properly. If you've enlarged the bore diameter, you'll definitely need to check, even if you purchased rings that are part- numbered for your specific bore diameter. File-fitting rings to obtain the precise end gaps required takes some knowledge. CHECK PISTON RING GAP First, organize all of your new rings, by cyl- inder, with top ring at the top, followed by second compression rings, followed by your oil ring packages, on a clean workbench. Using a clean, lint-free towel or rag, wipe each cylinder clean to remove oil/dust etc. Start with the top compression rings. One cylinder at a time, carefully compress the ring and insert the ring into the bore, about 1/2-inch below the deck. You must now square the ring in the bore (the ring must be placed evenly and equidistant around its entire circumfer- ence, relative to the block deck). To do this, you can use a dial caliper. Extend the caliper's rule (the end that you would use to measure depth) to about 3/4-inches or so and tighten the caliper's set screw. Walking around the perimeter of the ring, gently push the ring down until the caliper's body contacts the deck. A very handy ring squaring tool makes this a breeze. I use the squaring tool made by Summit Racing. It's adjustable for bore diameter and is stepped. Simply loosen the set screw, slide it apart to fit the bore diameter and tighten the set screw. Now the tool is ready to measure all eight cylinders. With the ring inserted near the top of the bore, place the tool into the bore. The lower portion of the tool contacts the ring, and when the upper shoulder contacts the block deck, the ring is squared. Remove the tool and using a feeler gauge, carefully measure the ring gap for all top and second rings. FILE-FITTING OE and aftermarket ring gaps may vary, depending on piston and/or ring source. If an off-the-shelf ring isn't available for your specific bore diameter/piston, or if you prefer to custom-fit rings anyway, slightly oversized file-to-fit rings are available that allow you to custom-tune ring end gap. If you have file-to-fit rings, you'll need to file-fit the top and second rings. You should check just to verify the end gaps of the oil ring rails, but you will not need to file-fit these rails. Oil ring rail end gaps will typi- cally be in the 0.015- to 0.031-inch range. EXAMPLES OF RING END GAP SPECS Citing JE Pistons gap recommendations as an example, desired end gap can vary depending on the intended engine applica- tion. Following is a guideline: For instance, if the cylinder bore diam- eter is 4.125 inches, and the application is high-performance street/strip use, the top ring end gap would be 4.125 X 0.0045, or 0.0185 inches. Second ring end gap would be 4.125 X 0.0050, or 0.020 inches. A diameter variance from one cylinder to the next changes the end gap of the rings in that cylinder by a factor of pi (3.1416). For example, a cylinder that is 0.001-inch larger in diameter will increase the ring end gap by 0.001 x 3.1416, or 0.003 inches. It's critical to always fit each ring for its specific cylinder. Instead of file-fitting all rings using one specific cylinder, in order to maximize uni- formity of your end gaps, dedicate a top ring and a second ring to each individual cylinder to accommodate any variance in bore diameter. In other words, file-fit a top and second ring to cylinder no. 1; file-fit rings at cylinder no. 2, etc. Keep all rings organized on a clean workbench on a per- cylinder basis. First, verify ring fit in its cylinder. Gently hand-compress the ring and insert it into the bore, just below deck. Square the ring in the bore using a measuring tool or a ring squaring tool. Verify that there is no gap (verifying that the ring must be filed to obtain a gap). FILING TIPS While you can obtain end gaps using a fine hand file, this is very tedious and time- consuming. A better option is to use a dedicated ring filer tool. These are available in manual-crank and electric versions. The bench-mount electric tools work great and save time, but are rather expensive. An option is a bench-mounted manual ring filer. This features a diamond abrasive Piston Ring Tech File-fitting and installation: obtaining ideal end gaps for performance engines. //////// By Mike Mavrigian APPLICATION TOP RING 2ND RING High perf. street/strip .................................. Bore X .0045" ........................... Bore X .0050" Street moderate turbo/nitrous .................... Bore X .0050" ........................... Bore X .0055" Late model stock ......................................... Bore X .0050" ........................... Bore X .0053" Circle track/drag race ................................. Bore X .0055" ........................... Bore X .0057" Nitrous race only ......................................... Bore X .0070" ........................... Bore X .0073" Blown race only ........................................... Bore X .0060" ........................... Bore X .0063" Oil ring rails: minimum gap of 0.015" After each piston and rod assembly has been fully installed, check crank rotation using a beam-type torque wrench, observ- ing how much torque is required.

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