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48 RICH FIELD FLYER CHRONOMETRIC TACHOMETER -BY- PVT. E. ROSENBERGER, "A" The purpose of the Van Sicken Chronometric Tachometer is to indicate constantly the speed in R. P. M. of the crankshaft of the motor, showing on the face of the instrument any increase or decrease in engine speed. The instrument gives its first reading on second after the motor has been started in motion and gives a new reading every second thereafter. As the camshaft speed is one-half of the crankshaft speed, the Chronometric Tachometer indicates twice the number of R. P. M., therefore it tells the actual R. P. M. of the motor crankshaft. The mechanism of the Chronometric Tachometer is made up of four primary groups of units as follows: A. The driving mechanics,. B. The power plant and the synchronizing cams. C. The watch mechanism. D. The counting mechanism. Use of Groups of Units. The driving mechanism takes the power from the flexible shaft, transmitting it to the power plant. The power plant furnishes the power for driving the watch mechanism, counting mechanism, and the synchronizing cams which time the action of the counting mechanism. The watch mechanism times the synchronizing cams. The counting mechanism counts the revolutions transmitted to it during periods of one second each and indicates results on the dial. The driving mechanism is operated by the case drive which takes the power from the flexible shaft and transmits it to the top gear of the idling unit through the worm gear. The idle unit merely transmits the power to the friction gear of the reversing unit. The reversing unit is composed of two gears mounted on a swiviled [[swiveled]] plate so that at all times it will drive the spring bar shaft in a clockwise direction regardless of the direction in which the case drive is being operated.. The bottom gear of the power plant takes the power from the reversing unit, and transmits it through a barrel shaft to the top gear. the top hear in turn drives the time level hear on the counting mechanism. The spring barrel furnishes power for driving the watch mechanism and synchronizing cams through the spring barrel gear. It is mounted free on the barrel shaft. The synchronizing cams are permanently fixed and rotate with the spring barrel. Incorporated in the spring barrel is a spring of the main spring type. One end of this spring is fastened to the barrel shaft, the other end being loose. As the barrel shaft rotates, the spring is wound up until a certain tension is reached, when the loose end starts slipping. As a result the power that the spring barrel transmits to the watch mechanism is always constant. The synchronizing cams which rotate with the spring barrel time the action of the lock levers and the time lever, which in turn times the action of the counting mechanism. The sole purpose of the intermediate unit is to transmit the power from the spring barrel to the fly pinion of the watch mechanism. The upper gear meshes with the spring barrel gear and the lower gear with the fly pinion gear. The operation of the watch mechanism is to time the synchronizing cams. The fly pinion receives is power from the lower gear of the intermediate unit and transmits it through the fly to the escape pinion. The friction disc is merely a shock absorber which prevents the fly from striking a heavy blow on the escape pinion, holding it so as to prevent rebounding. Heavy Jeweled Balance. The watch escapement is of the regular type. The compensating balance is the regular balance used in watches but of heavier construction, and is jeweled in the regular way. In counting mechanism, the gear of the time lever of the timing mechanism takes its power from the top gear of the power plant and transmits it through the lower gear of the time lever to the counting gear of the counting mechanism. This power is applied to the counting gear for a period of one second when the time lever is thrown out by the action of the synchronizing cams. It must be remembered that the top gear of the power plant is directly connected through the driving mechanism to the flexible shaft and therefore has a proportionate speed which is transmitted to the counting gear. As a result, the counting gear is driven in a clockwise direction to a point determined by the speed at which the instrument is being driven. At the same time the lever is thrown out the top lock lever falls into position and locks the counting gear units advanced position. For the first second that the instrument is in operation the hand gear which carries the indicating arm on the dial with it, is carried up with the counting gear by the action of the top and bottom stop pins and the bottom stop arm. As the top lock lever is momentarily thrown out releasing the hand gear so that if in any cycle the speed of the instrument is decreased the hand gear will fall back as a resut [[result]] of the action if spring to new position, holding the hand gear in position to which is was driven by the counting gear, or to which it fell back. Thus the hand gear through its permanently fixed indicating arm indicates the speed on the dial holding it for the duration of the cycle when the hand gear is again released to take up a new position of the counting gear. While the hand gear is being held by the lower lock lever the counting gear is released, falls back to the ero point as a result of the action of the spring and take sup the new speed being transmitted to the instrument. This instrument is the only tachometer made that will give the true R. P. M. of the motor. -- Retempered Engine Springs -By- Lt. Wallace G. Imhoff Noisy valve action can often be traced directly to weak springs. With only a few engines the retempering of worn out springs would not be practical but where there are large numbers of engines being overhauled every day it is a practical problem worth looking into. Such was the case here at Rich Field, Waco, Texas; there were about four hundred old springs which were ready for the Salvage Officer. The reclaiming of such a large number of intake, exhaust, and push rod springs meant quite a practical problem and as the retempering was carried out successfully it will be of interest to describe the process. At first it did not seem like a very difficult problem but after starting one thing after another developed which showed us we had a large number of things to overcome before we could hope for success. Some of the difficulties that it is absolutely essential to watch with the greatest of care are oxidation, proper quenching temperature, handling of the springs when white hot, uniform heating of spring all over and proper drawing temperature. The first procedure is to pull the springs back to their original length when cold. This is important, for the springs show different strength under different lengths. The heating oven consists of a six-inch iron pipe which has a back welded on it and a piece of iron place which is used for a front door is stood against the front end. The pipe is placed in an ordinary forge fire and the coals heaped clear up around the pipe over the top for about four to six inches. All during the operation the pipe is continually turned over and over to insure uniform heat throughout. Temper With Fish Oil. The tempering is done in a large galvanized iron can which contains fish oil. Inside the can is a neat-fitting wire screen basket with a handle on each side so that it can be easily raised and lowered in the can. The oil must be a good grade of fish oil and not oil which has been used and he life has been taken out of it. One of the worst features to deal with is the rapid oxidation of the steel springs when brought to high heat. Therefore, it is necessary that the operation be carried out in a reducing atmosphere that is one which has no air at all or at least as little as possible. To obtain such conditions small pieces of coke are placed in the bottoms of the pipe about one inch deep. Thus any oxygen which has gotten in with air is immediately taken up by the coke to form carbon monoxide and carbon dioxide depending on the quantity of air which enters the pipe. The question of oxidation is perhaps one of the most important things to be watched during the operation. It is surprising how quickly the steel scales up if this precaution is not closely followed. A scale on the spring means a reduction in size and therefore decreased strength. The quality of steel used in the springs makes it necessary to bring them up to a bright yellow heat before removing to be quenched in the oil. A red hear was not sufficient to produced the desired results. Care should be taken that the springs are not crowed together or touch each other for when they are white hot they have no strength and the smallest strain will pull them out of shape or change their length. It is not a fast process nor can you make much progress by trying to handle the springs in large numbers. From six to eight at a time in the pipe give good results and with practice about two hundred springs is a good days work if all are tempered properly. (Continued on Page 56)
