Depreciation in Valve Operating Systems.-There are a number of points to be watched in the valve operating system because valve timing may be seriously interfered with if there is much lost motion at the various bearing points in the valve lift mechanism. The two conventional methods of opening valves are shown at Fig. 123. That at A, is the type employed when the valve cages are mounted directly in the head, while the form at B, is the system used when the valves are located in a pocket or extension of the cylinder casting as is the case if an L, or T-head cylinder is used. It will be evident that there are several points where depreciation may take place. The simplest form is that shown at B, and even on this there are five points where lost motion may be noted. The periphery of the valve opening cam or roller may be worn. though this is not likely unless the roller or cam has been inadvertently left soft. The pin which acts as a bearing for the roller may become worn, this occurring quite often. Looseness may materialize between the bearing surfaces of the valve lift plunger and the plunger guide casting and there may also be excessive clearance between the top of the plunger and the valve stem.

On the form shown at A, there are several parts added to those indicated at B. A walking beam or rocker lever is necessary to transform the upward motion of the tappet rod to a downward motion of the valve stem. The pin on which this member fulcrums may wear as will also the other pin acting as a hinge or bearing for the yoke end of the tappet rod. It will be apparent that if slight play existed at each of the points mentioned it might result in a serious diminution of valve opening. Suppose, for example, that there were .005-inch lost motion at each of three bearing points, the total lost motion would be .015-inch or sufficient to produce noisy action of the valve mechanism. When valve plungers of the adjustable form, such as shown at B, are used, the hardened bolt head in contact with the end of the valve stem may become hollowed out on account of the hammering action at that point. It is imperative that the top of this member be ground off true and the clearance between the valve stem and plunger properly adjusted. If the plunger is a non-adjustable type it will be necessary

to lengthen the valve stem by some means in order to reduce the excessive clearance. The only remedy for wear at the various hinges and bearing pins is to bore the holes out slightly larger and to fit new hardened steel pins of larger diameter. Depreciation between the valve plunger guide and the valve plunger is usually remedied by fitting new plunger guides in place of the worn ones. If there is sufficient stock in the plunger guide casting as is always the case when these members are not separable from the cylinder casting, the guide may be bored out and bushed with a light bronze bushing.

Another point where depreciation must be looked for is between the valve stem and the valve stem guide in the cylinder. The methods of repairing this defect are clearly indicated at Fig. 124. A common cause of irregular engine operation is due to a sticking valve, which condition is clearly depicted at Fig. 123, C. This may be due to a bent valve stem, a weak or broken valve spring or an accumulation of burnt or gummed oil between the valve stem and the valve stem guide. In order to prevent this the valve stem must be smoothed with fine emery cloth and no burrs or shoulders allowed to remain on it, and the stem must also be straight and at right angles to the valve head. If the spring is weak it may be strengthened in some cases by stretching it out so that a larger space will exist between the coils. Obviously if a spring is broken the only remedy is replacement of the defective. member.

A number of engines of old patterns had cams keyed to the camshaft instead of formed integrally with it as is now common practice. After the engine had been used for a time, especially if the valve springs were stiff, the key was very apt to become loose in the cam which would result in a pronounced knock when the engine was in operation. The reason for this knock may be clearly understood by referring to illustration at Fig. 123, D. With the key slot worn, as the cam started to lift the plunger the pressure against the cam would cause that member to come back against the key sharply and the hammering action would cause noise. Similarly when the cam left the plunger the looseness would again be evidenced and another knock would result. Where

this form of fastening is used the only remedy for worn keyway in the cam is to use wider keys in the camshaft by providing new keyways in that member. While it is possible to cure the trouble by using a two diameter key, this is not considered good practice owing to difficulties in properly fitting such a member.

Mention has been made of wear in the valve stem guide and its influence on engine action. When these members are an integral part of the cylinder the only method of compensating for this wear is to drill the guide out and fit a bushing, which may be made of steel tube. In order to insure that the hole will be bored out true a simple jig is extemporized from one of the valve chamber caps as indicated. The cap used is the member carrying the spark plug and the opening left for this member is filled with a threaded bushing carrying a plain hardened steel bushing intended for the drill guide. As it is not always possible to procure steel tubing of the proper size it may be necessary to drill out or ream out the bore of the tube to fit the valve stem after the bushing is driven in place.

In most engines, especially those of recent development, the valve stem guide is driven into the cylinder casting and is a separate member which may be removed when worn and replaced with a new one. When the guides become enlarged to such a point that considerable play exists between them and the valve stems, they may be easily knocked out by using a drift pin of the proper size and a hammer or forced out under an arbor press. This is not a difficult thing to do, as one need not be afraid of injuring a member which is no longer of any use. Care must be taken, however, in placing the new valve stem guide because, while this might be hammered in place, it could not be done unless extreme care was exercised and there would always exist the possibility of injuring the guide. The approved method of installing a new valve stem guide is shown at Fig. 124, C. A cold rolled steel rod is threaded practically its entire length and is of sufficient diameter to just fit into the hole in the guide. A substantial piece of flat stock E, is placed over the valve chamber, this being at least one-quarter inch thick and one inch wide and of such length as to bridge the valve cap opening over and leave a liberal margin

at either side. The nut A, is screwed down on the rod B, until the nut C, at the lower end of the rod is bearing tightly against the valve stem guide G. The guide member is then forced into place by turning either or both of the nuts A, or C, until it is firmly seated. It is possible to use a long bolt instead of the rod B, if desired. When this system of valve guide construction is followed, the work of replacing the worn members can be

Fig. 124.-Practical Methods of Restoring Worn Valve Stem Guide

Bushing.

done by one without mechanical experience just as well as by the more expert.

The depreciation of the exposed valve stem guides may be reduced considerably by adopting the scheme for lubricating the valve stems shown at Fig. 124, E, used on Overland cars. This consists of cutting out the lower portion of the valve stem guide to take a beveled felt washer which is kept firmly pressed against the seating by a cupped steel washer maintained in contact against the felt by a coil spring extending down to the valve spring collar and fitting the valve stem fairly close. The shape of the cupped