The interest of the repair man in all these valve-motion parts is quite different from that of the designer, for he cares not so much how they are made as how they are taken out, repaired, and put back, when accident or wear make this work necessary. To the repair man suitable tools for doing this, kind of work are also of interest, particularly those for reaching inaccessible parts or for doing things which without the tools could not be done.
Valve springs and the valves themselves, either at the seat end or at the tappet end, give the most trouble. For example, when the clearance between the end of the tappet and the end of the valve (usually from 3/1000 to 8/1000 inch) is too great, a metallic click results. Often this noise from the tappet is mistaken for a motor knock; but the skilled repair man has little trouble in finding and remedying it, for even if he cannot measure in thousandths of an inch, he knows, for instance, that the ordinary cigarette paper is about 3/1000 inch in thickness and from this he can estimate 3/1000,6/1000 or 9/1000 inch. Ordinary thin wrapping paper is well known to be about 5/1000 inch; with this alone, or in combination with cigarette papers he can obtain 5/1000, 8/1000,10/1000 and 1/1000 inch, practically all the variation he is likely to need.
Fig. 26. Bent Tool Which Facilitates Removal of Stuck Valves.
Getting the valve out frequently gives much trouble, the valve often being found frozen to its seat or with the stem gummed in its guide. A tool to meet this difficulty is a plain bar or round iron about ¼ inch in diameter, Fig. 26, with one end, for a distance of perhaps 2 or 2½ inches, bent up at an angle of about 120 degrees. To use the tool, insert the short bent end in the exhaust or the inlet opening, according to which valve is stuck, until the end touches the under side of the valve head, then lower the outer end until the bottom of the bent part or point at which the bend occurs rests against solid metal. The outer end can now be pressed down, and with the inner end acting as a lever the valve can be pressed off its seat and out very quickly.
To make this clearer, the rod, Fig. 26, is indicated at A, while the dotted line shows how it is pressed down and the valve forced out. The garage man can elaborate upon the tool when making it for himself by using square stock and having the inner end forked so as to bear on each side of the valve. The form pointed out above is the simplest, cheapest, and easiest to make.
Taking out the valve spring is frequently difficult for various reasons; perhaps the springs are very stiff, or they may have rusted to the valve cups at the bottom, or the design may not allow room enough to work, etc. At any rate the removal is difficult, and a tool which will help in this and which is simple and cheap, is in demand. Many motor cylinders are cast with a slight projection or shelf opposite the valve spring positions, so that one only needs a tool that will encircle the lower end of the valve spring and rest upon this ledge, and give an outer leverage.
In working on cylinders that do not have this cast projection, a tool like that shown in Fig. 27 is useful. It consists of a yoke for encircling the lower end of valve spring and cup, with a long outer arm for prying, and a slot into which is set a drilled bar. This bar is placed in various positions according to the kind of motor which is being worked on; when removing a valve-spring key, the lower end of the bar rests upon the crankcase upper surface, or upon the push-rod upper surface if that is extended. After slipping the grooved yoke under the spring cup, a simple pressure on the outer end raises the valve so the key can be withdrawn. Then the removal of the tool allows the valve spring to drop down, and the valve is free.
Fig. 27. Easily Made Tool for Removing Volvo Spring.
The valve spring may be removed in two other ways by the use of the two tools shown in Figs. 28 and 29. In the former, the idea is to compress the spring only, no other part being touched. This tool once set, will continue to hold the spring compressed, leaving the hands free - a decided advantage over the tool shown in Fig. 27. This device consists, as the illustration shows, of a pair of arms with forked inner ends and outer ends joined by a pin. A bent handled screw draws the ends together or separates them according to which way it is turned.
The simplest tool of all is the one shown in Fig. 29, simply a formed piece of stiff sheet metal which is set into place when the valve is open. Then when the valve is closed by turning the motor, the sheet metal piece holds the spring up in its compressed position.
Many times there is a need for holding the spring in its compressed form, as, for instance when the valve is removed with the positive certainty that it will be replaced within four or five minutes. In such a case a clamp which will hold it in compression is very useful for it saves both time and work. These may be made to the form shown in Fig. 30 in a few minutes' time, for they consist simply of a pair of sheet metal strips with the ends bent over to form a very wide U shape. A pair of these is made for each separate make of valve spring, because of the varying lengths, but as they are so easily and quickly made this is no disadvantage.
Fig. 28. Type of Valve-Spring Tool Which Leaves the Honda Free.
Fig. 29. A Substitute for a Valve Spring Remover Which pushes Spring Away as Motor is Turned.
In many shops, after getting in the habit of making these clamps, the workmen take this way of replacing the spring in preference to all others. After removal of the valve, the spring may be compressed in a vise and a pair of the clamps put on. Then when the valve is ready to go back in, the spring is as easy to handle as any other part. This is especially true when replacing the spring retainer and its lock.
Many times when valve springs become weakened, they can be stretched to their former length, so that their original strength is restored. This can be done by removing them and stretching each individual coil, taking care to do it as evenly as possible. When well stretched, it is advisable to leave the coils that way for several days. This method will not, of course, restore the strength permanently; it is at best a makeshift, for in the course of a few thousand miles the springs will be as bad as before.
Sometimes weakened valve springs may be renewed by retem-pering, on the theory that the original temper was not good or they would not have broken down in use. The tempering is done by heating to a blood-red color and quenching in whale oil. If this is not successful, new springs are advised.
Unless all the valves on a motor agree, it will run irregularly - that is, all the exhausts must be of the same tension, and all the inlets must agree among themselves, though not necessarily with the exhausts. Many times irregular running of this kind, called "galloping", is more difficult to trace and remove than missing or other more serious troubles, and it is fully as annoying to the owner as missing would be.
Fig. 30. Spring Clamp, Which Is Easily Made and SavesMuch Work and Trouble.
To be certain of finding this trouble, the repair man should have a means of testing the strength of springs, a simple device being shown in Fig. 31. As will be seen, this consists of sheet-metal strips and connecting rods of light stock, with a hook at the top for a spring balance and a connection at the bottom to a pivoted hand lever for compressing the spring. By means of the center rod at R and the thumb screw at the bottom, the exact pressure required to compress the spring to a certain size may be determined. Thus, suppose the spring should compress from 4 inches to 3½ inches under 50 pounds. By compressing it in the center portion of the device, so that the distance between the two adjacent strips of metal indicated by S is just 3½ inches, the spring balance should show just 50 pounds. If it shows any less, the spring is too weak and should be discarded; if it shows any more, it is stronger than normal - which is desirable if all the other springs on the same engine are stronger also.
If only a quick comparison of four springs is desired, the device can be made without the bottom lever, as the setting of S at a definite figure - say to a template of exact length - would call for a certain reading of the scale of the spring balance.
Cutting valve key slots in valve stems is another mean job, which the repair man frequently meets. He runs across this in repairing old cars for which he has to make new valves and at other times. The best plan is to make a simple jig which will hold, guide, and measure, doing all these things at once as all are important. Such a jig is shown in Fig. 32. It consists of a piece of round or other bar stock, in which a central longitudinal hole is drilled to fit the valve stem, one end being threaded for a set screw. Near the other end of the jig, three holes are drilled in from the side, of such a diameter as to correspond with the width of key slot desired. These are so placed that the length from the top of the upper hole to the bottom of the lower gives the length of key seat desired. Opposite the three drilled holes and at right angles to them another hole is drilled and tapped for a set screw. To use the device, slip the valve in place and set the bottom screw of the jig so as to bring the three drilled holes at the correct height for the location of the key seat. Then the three holes are drilled, and the valve is moved upward so that the space between the holes is opposite a guide hole, and two more holes are drilled to take out the metal between. The five holes will give a fairly clean slot, which only needs a little cleaning up with a file, before using.
Fig. 31. Simple Rigging for Testing Valve Spring Pressure and Strength.