![]() It is a safe practice once the rings are fitted to the pistons to recheck with a small straight edge. This method allows this check to be carried out before fitting the rings to the pistons. The easiest way to do a quick check of ring back clearance is to place the ring backwards in the ring groove and visually confirm that it is below the ring land outer edge. ![]() Ring back clearance…… Whenever rings are procured from different manafacturers than the pistons some differences can occur. Use a feeler gauge to align the end gaps. Oil rail end gap…… The easiest way to check these is to place all the rails together in the bore with all the end gaps lined up. If ring end gap is under minimum and piston to bore clearance is correct the rings should be replaced or the end gaps filed to size. It is more important not to be under the minimum clearance as ring seizure and breakage will occur as the rings heat up to normal operating temperature. Up to 50% above these specifications will usually be acceptable. Different ring manafacturers use nominal bore size to manufacture their rings and as pistons can vary in size from one manufacturer to another the minimum is often not achieved. So a 3 inch bore should have a minimum ring gap of. (0.1 mm per 25mm of bore)This general rule is fine for bores from 2.5 inches to 4.5 inches. The minimum end gap is calculated using a general rule of. If they are removed unevenly breakage or damage could occur. Use caution when removing the loose rings. Check all the compression rings in this manner. Remove the piston and measure the ring end gap with feeler strips. Simply place the ring in the bore and take the piston, facing the crown against the ring easing it down the bore until it is square. This is achieved by using the piston crown as a guide to push the loose ring down the bore. To obtain accurate measurements the ring has to be placed very squarely in the cylinder. Care has to be taken when fitting the rings in the bore for measurement. This procedure is simple enough but is of utmost importance. Requirements pertaining to the installation and use of all boxes and conduit bodies used as outlet, device, junction or pull boxes are in Article 314 of the National Electrical Code.Ring end gap……The next measurement is the end gap on the supplied rings. Besides boxes and conduit bodies, this article covers manholes and other electric enclosures intended for personnel entry. Article 314 also includes installation requirements for fittings used to join raceways and to connect raceways and cables to boxes and conduit bodies. After providing an introduction of Article 314, last month’s In Focus covered 314.15 and started discussing provisions in 314.16. Just because a cover can be installed on a junction box that is packed full of conductors, does not mean it is Code compliant. Requirements in 314.16(A) and (B) specify how to calculate the maximum number of conductors in outlet, device, pull or junction boxes. While box volume calculations are in 314.16(A), box fill calculations are in 314.16(B). The volume of the box, as calculated in 314.16(A), must not be less than the fill calculation as calculated in 314.16(B). Table 314.16(A) provides minimum volume and maximum number of conductors for certain size metal boxes. Table 314.16(A)’s middle section provides the cubic-inch and cubic-millimeter volume for each box trade size. Volume is not calculated by using the outside dimensions of a box. The volume is the actual amount of area or space inside the box. For example, what is the cubic-inch volume of a 4-inch square metal box with a depth of 1 1/2 inches? By using the outside dimensions, the size of the box is 24 cubic inches (4 x 4 x 1.5 = 24). However, this is not the cubic-inch volume of the box. As listed in Table 314.16(A), a 4-inch square metal box with a depth of 1 1/2 inches has a volume of 21 cubic inches (See Figure 1). When the same size conductors will be installed in a metal box that is listed in Table 314.16(A), no calculation is needed. First, find the box and then follow the row across to find the maximum number of conductors permitted.
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