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Show si no of m 13 INI ITSELF It is just as important to know when not to grind a valve as to know when grinding is necessary, is the sound advice given by Arnold P. Yerke in an article on "Valve Inspection and Grinding," in August M0T0H. It is quite well known by many motorists that not all engines run better after the valves have been ground, a fact which is attributed to the unnecessary grinding which makes for leaky valves. The writer in his article points out how one may. distinguish a valve that leaks from one that docs not, and tells how only the faulty ones should be ground in. He says: "On a properly oooled engine and one where the valves are properly timed, it may be accepted as a general rule that valves which are evenly sooted over and, therefore, have perfectly black heads, are holding, while those which are red or brownish on top, or show the metal plainly, without a covering cov-ering of soot or carbon, are leaking. By observing the tops of the valve heads as soon as the cylinder head is removed and then carefully inspecting the lace of the valve and the seat, one will quickly learn to tell what is needed. "The reason for the difference in the looks of the tops is simple and obvious upon a little thought. During the power stroke of the piston the burning gases are under high pressure. If there is the slightest leak at any point around the face of the valve, the gases will force their way through at terrific speed and carry away any carbon which may have been formed on the top of the valve near the leak, as well as on the casting near the valve seat, leaving the metal around the leak entirely clear of soot or carbon. car-bon. Not only will the escaping gjis carry away all carbon near the leak, hut will also actually wear away the metal itself if not attended to. "A valve which is allowed to leak for n long time will f requ e n 1 1 y si i o w quit e a path eroded by the hot gases in rushing through the opening, in much the same way as the gases from the burning powder pow-der charges in a high-power rifle or cini-non cini-non gradually erode the metal of Urn rifie or cannon barrel by escaping past the projectile before it pets fully "under way. The paths cut by these gass in either case look almost as though the metal hnd bee n me 1 ted ou t , nod t h e re is undoubtedly a certain amount of melting of the metal brought about by the hot gapps. "The high temperature of the escaping gases als( cause a different color of the metal uronnd a leaky valve in man, c:i -es. Very frequently a lea ky valve will have a. reddish a ppearan.'-e, hkc burned clay or like u fnruai-e graio oft-n s; how. after being und r a very hot fin1 for some lime. This is not mi rifnilible. ' rule for deleting a U-;tky valve. It. it. on many engims it is a Very reliable indication." |