Ring End Gap
Checking ring gaps
ENGINE ASSEMBLY HINTS
Ring end gap……The next measurement is the end gap on the supplied rings. This procedure is simple enough but is of utmost importance. Care has to be taken when fitting the rings in the bore for measurement. To obtain accurate measurements the ring has to be placed very squarely in the cylinder. This is achieved by using the piston crown as a guide to push the loose ring down the bore. 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. Remove the piston and measure the ring end gap with feeler strips. Check all the compression rings in this manner. Use caution when removing the loose rings. If they are removed unevenly breakage or damage could occur.
The minimum end gap is calculated using a general rule of .004 of an inch per inch of bore. (0.1 mm per 25mm of bore)This general rule is fine for bores from 2.5 inches to 4.5 inches. So a 3 inch bore should have a minimum ring gap of .012 of an inch.(0.3mm). 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. Up to 50% above these specifications will usually be acceptable. 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. 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.
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. Use a feeler gauge to align the end gaps. Anywhere between .040″ (1mm) and .070″ (1.75mm) is acceptable.
Ring back clearance…… Whenever rings are procured from different manafacturers than the pistons some differences can occur. 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. This method allows this check to be carried out before fitting the rings to the pistons. It is a safe practice once the rings are fitted to the pistons to recheck with a small straight edge.
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