Arizona republican., 1918-01-20
VALVE GEARS

The automobile engine is much like a human being in one particular i.s functional we'll being is largely de- pendent on a respiratory system ny this expression, we mean that part or it's mechanism that has to do with breathing in of the fuel vapor and the eynelling of the burned gases aftef combustion has taken place. inc res- piratory function of the engine is con- troIIed by the valves. If the valves which permit the fuel to enter the combustion chamber do not peT1orh their work properly, much Of the pow CT of the motor will obviously De lost. Again it is just as important to get the burned gases out or the way altel combustion, for their continued pres ence in the combustion chamber Will contaminate the fresh fuel. Grantlps then, the importance of the valve sys- tenn. a brief study of the unit, its com mon failings and how to remedy them may be interesting and helpful.
 To begin with here are five definite tvpes of valve gears. The most popu- lar type consists of a single camshaft, operating pushrods, which directly control the valves. This IS the type that is used on L-head engines, by lar the commonest type of power plant. The next type is the valve-ln-head, which means that the valves are To- cated in the heads of the cylinders, the operation being achieved by means of vertical rods and rocker arms. These rocker arms are merely plvoted levers. operated from vertical rods, which extend up from push rod, driven by an ordinary camshaft. Ihe next valve type is known as the T. head. which operates on the same nrinciule as the L-head, but has two camshafts, one for intake and the other for exhaust valves. The fourth type also has valves in the heads of the cylinders, but the camshaft is placed on top of the cylinders, instead of being in the crankcase. The final tyne is the sleeve valve, which are simply ports in sliding sleeves which are actuated by eccentric shafts, cor rasponding to the camshafts of ordin- ary practice.
 Most car owners understand some thing of the way in which valves are operated. but we shall describe the operation briefly. The cAnshaft is geared to the crankshaft and as it re- wolves, the cams are brought into con- tact with the valve litter, which is cylinder bit of steel, moving up and down within a guide. As the litter is forced upward it pushes the valve open. against the resistance of a spring. When it reaches it's limit of upward movement. it sinks down again and the spring closes the valve. Obviously the position and size of the cams and other parts of the valve gearing must be accurately determined to keep the valve open for just the proper length of time. Also the valves must open at exactly the right instant in relation to the position of the piston. It will be evident that wear in certain parts of this valve system, will cause derange- ment of the entire operation of the respiratory system of the engine.
 The modern tendency in engine de- sign is to keep the entire valve mech l anism exposed to a perpetual spray of oil. In some designs pipes are pro- vided, but in others the valve system is located inside the crankcase, where it gets splash fabrication from the connecting rods. As a result of this tendency the wear and consequent noisy operation of the valve system which used to be almost universal, has l been largely eliminated. Nevertheless the average car owner does not give i his valve system the care or rather watching that it needs and small things often develop into big failures, for lack l of a small attention in time.
 For instance, it is not uncommon to find an excessive leakage of oil l down the sides of the valves. This is
 caused by wear of the valve stem or
 stem guide, usually brought about by insufficient fabrication. Something
 may have prevented oil from getting tc
 the mechanism and the result has been
 excessive and rapid wear. Or the con-
 dition may be caused by the fact that 1 the valve is pushed sideways when ever it is raised, because of Q bent stem, worn tappet or stem bottom. It l frequently happens that the stem will
 be struck at one point only, inducing excessive side thrust, wearing the valve
 stem guide. When the guides have 1 been worn in thic way if ic ,,acc;hlo +~