Some of the various designs of connecting rods that have been used are shown at Fig. 128. That at A is a simple form often employed in single-cylinder motors, having built-up crank-shafts. Both ends of the connecting rod are bushed with a one-piece bearing, as it can be assembled in place before the crank-shaft assembly is built up. A built-up crank-shaft such as this type of connecting rod would be used with is shown at Fig. 106. The pattern shown at B is one that has been used to some extent on heavy work, and is known as the “marine type.” It is made in three pieces, the main portion being a steel forging having a flanged lower end to which the bronze boxes are secured by bolts. The modified marine type depicted at C is the form that has received the widest application in automobile and aviation engine construction. It consists of two pieces, the main member being a steel drop forging having the wrist-pin bearing and the upper crank-pin bearing formed integral, while the lower crank-pin bearing member is a separate forging secured to the connecting rod by bolts. In this construction bushings of anti-friction metal are used at the lower end, and a bronze bushing is forced into the upper- or wrist-pin end. The rod shown at D has also been widely used. It is similar in construction to the form shown at C, except that the upper end is split in order to permit of a degree of adjustment of the wrist-pin bushing, and the lower bearing cap is a hinged member which is retained by one bolt instead of two. When it is desired to assemble it on the crank-shaft the lower cap is swung to one side and brought back into place when the connecting rod has been properly located. Sometimes the lower bearing member is split diagonally instead of horizontally, such a construction being outlined at E.
Fig. 128.—Connecting Rod Types Summarized. A—Single Connecting Rod Made in One Piece, Usually Fitted in Small Single-Cylinder Engines Having Built-Up Crank-Shafts. B—Marine Type, a Popular Form on Heavy Engines. C—Conventional Automobile Type, a Modified Marine Form. D—Type Having Hinged Lower Cap and Split Wrist Pin Bushing. E—Connecting Rod Having Diagonally Divided Big End. F—Ball-Bearing Rod. G—Sections Showing Structural Shapes Commonly Employed in Connecting Rod Construction.
In a number of instances, instead of plain bushed bearings anti-friction forms using ball or rollers have been used at the lower end. A ball-bearing connecting rod is shown at F. The big end may be made in one piece, because if it is possible to get the ball bearing on the crank-pins it will be easy to put the connecting rod in place. Ball bearings are not used very often on connecting rod big ends because of difficulty of installation, though when applied properly they give satisfactory service and reduce friction to a minimum. One of the advantages of the ball bearing is that it requires no adjustment, whereas the plain bushings depicted in the other connecting rods must be taken up from time to time to compensate for wear.
This can be done in forms shown at B, C, D, and E by bringing the lower bearing caps closer to the upper one and scraping out the brasses to fit the shaft. A number of liners or shims of thin brass or copper stock, varying from .002 inch to .005 inch, are sometimes interposed between the halves of the bearings when it is first fitted to the crank-pin. As the brasses wear the shims may be removed and the portions of the bearings brought close enough together to take up any lost motion that may exist, though in some motors no shims are provided and depreciation can be remedied only by installing new brasses and scraping to fit.
The various structural shapes in which connecting rods are formed are shown in section at G. Of these the I section is most widely used in airplane engines, because it is strong and a very easy shape to form by the drop-forging process or to machine out of the solid bar when extra good steel is used. Where extreme lightness is desired, as in small high-speed motors used for cycle propulsion, the section shown at the extreme left is often used. If the rod is a cast member as in some marine engines, the cross, hollow cylinder, or U sections are sometimes used. If the sections shown at the right are employed, advantage is often taken of the opportunity for passing lubricant through the center of the hollow round section on vertical motors or at the bottom of the U section, which would be used on a horizontal cylinder power plant.
Connecting rods of Vee engines are made in two distinct styles. The forked or “scissors” joint rod assembly is employed when the cylinders are placed directly opposite each other. The “blade” rod, as shown at Fig. 129, fits between the lower ends of the forked rod, which oscillate on the bearing which encircles the crank-pin. The lower end of the “blade” rod is usually attached to the bearing brasses, the ends of the “forked” rod move on the outer surfaces of the brasses. Another form of rod devised for use under these conditions is shown at Fig. 130 and installed in an aviation engine at Fig. 132. In this construction the shorter rod is attached to a boss on the master rod by a short pin to form a hinge and to permit the short rod to oscillate as the conditions dictate. This form of rod can be easily adjusted when the bearing depreciates, a procedure that is difficult with the forked type rod. The best practice, in the writer’s opinion, is to stagger the cylinders and use side-by-side rods as is done in the Curtiss engine. Each rod may be fitted independently of the other and perfect compensation for wear of the big ends is possible.
Fig. 131.—Part Sectional View of Wisconsin Aviation Engine, Showing Four-Bearing Crank-Shaft, Overhead Cam-Shaft, and Method of Combining Cylinders in Pairs.
Fig. 132.—Part Sectional View of Renault Twelve-Cylinder Water-Cooled Engine, Showing Connecting Rod Construction and Other Important Internal Parts.
CAM-SHAFT AND CRANK-SHAFT DESIGN
Before going extensively into the subject of crank-shaft construction it will be well to consider cam-shaft design, which is properly a part of the valve system and which has been considered in connection with the other elements which have to do directly with cylinder construction to some extent. Cam-shafts are usually simple members carried at the base of the cylinder in the engine case of Vee type motors by suitable bearings and having the cams employed to lift the valves attached at intervals. A typical cam-shaft design is shown at Fig. 133. Two main methods of cam-shaft construction are followed—that in which the cams are separate members, keyed and pinned to the shaft, and the other where the cams are formed integral, the latter being the most suitable for airplane engine requirements.
Fig. 133.—Typical Cam-Shaft, with Valve Lifting Cams and Gears to Operate Auxiliary Devices Forged Integrally.
The cam-shafts shown at Figs. 133 and 134, B, are of the latter type, as the cams are machined integrally. In this case not only the cams but also the gears used in driving the auxiliary shafts are forged integral. This is a more expensive construction, because of the high initial cost of forging dies as well as the greater expense of machining. It has the advantage over the other form in which the cams are keyed in place in that it is stronger, and as the cams are a part of the shaft they can never become loose, as might be possible where they are separately formed and assembled on a simple shaft.
Fig. 134.—Important Parts of Duesenberg Aviation Engine. A—Three Main Bearing Crank-Shaft. B—Cam-Shaft with Integral Cams. C—Piston and Connecting Rod Assembly. D—Valve Rocker Group. E—Piston. F—Main Bearing Brasses.
The importance of the crank-shaft has been previously considered, and some of its forms have been shown in views of the motors presented in earlier portions of this work. The crank-shaft is one of the parts subjected to the greatest strain and extreme care is needed in its construction and design, because practically the entire duty of transmitting the power generated by the motor to the gearset devolves upon it. Crank-shafts are usually made of high tensile strength steel of special composition. They may be made in four ways, the most common being from a drop or machine forging which is formed approximately to the shape of the finished shaft and in rare instances (experimental motors only) they may be steel castings. Sometimes they are made from machine forgings, where considerably more machine work is necessary than would be the case where the shaft is formed between dies. Some engineers favor blocking the shaft out of a solid slab of metal and then machining this rough blank to form. In some radial-cylinder motors of the Gnome and Le Rhone type the crank-shafts are built up of two pieces, held together by taper fastenings or bolts.
Fig. 135.—Showing Method of Making Crank-Shaft. A—The Rough Steel Forging Before Machining. B—The Finished Six-Throw, Seven-Bearing Crank-Shaft.
The form of the shaft depends on the number of cylinders and the form has material influence on the method of construction. For instance, a four-cylinder crank-shaft could be made by either of the methods outlined. On the other hand, a three- or six-cylinder shaft is best made by the machine forging process, because if drop forged or cut from the blank it will have to be heated and the crank throws bent around so that the pins will lie in three planes one hundred and twenty degrees apart, while the other types described need no further attention, as the crank-pins lie in planes one hundred and eighty degrees apart. This can be better understood by referring to Fig. 135, which shows a six-cylinder shaft in the rough and finished stages. At A the appearance of the machine forging before any of the material is removed is shown, while at B the appearance of the finished crank-shaft is clearly depicted. The built-up crank-shaft is seldom used on multiple-cylinder motors, except in some cases where the crank-shafts revolve on ball bearings as in some automobile racing engines.
Crank-shaft form will vary with a number of cylinders and it is possible to use a number of different arrangements of crank-pins and bearings for the same number of cylinders. The simplest form of crank-shaft is that used on simple radial cylinder motors as it would consist of but one crank-pin, two webs, and the crank-shaft. As the number of cylinders increase in Vee motors as a general rule more crank-pins are used. The crank-shaft that would be used on a two-cylinder opposed motor is shown at Fig. 136. This has two throws and the crank-pins are spaced 180 degrees apart. The bearings are exceptionally long. Four-cylinder crank-shafts may have two, three or five main bearings and three or four crank-pins. In some forms of two-bearing crank-shafts, such as used when four-cylinders are cast in a block, or unit casting, two of the pistons are attached to one common crank-pin, so that in reality the crank-shaft has but three crank-pins. A typical three bearing, four-cylinder crank-shaft is shown at Fig. 134, A. The same type can be used for an eight-cylinder Vee engine, except for the greater length of crank-pins to permit of side by side rods as shown at Fig. 137. Six cylinder vertical tandem and twelve-cylinder Vee engine crank-shafts usually have four or seven main bearings depending upon the disposition of the crank-pins and arrangement of cylinders. At Fig. 138, A, the bottom view of a twelve-cylinder engine with bottom half of crank case removed is given. This illustrates clearly the arrangement of main bearings when the crank-shaft is supported on four journals. The crank-shaft shown at Fig. 138, B, is a twelve-cylinder seven-bearing type.
Fig. 138.—Crank-Case and Crank-Shaft Construction for Twelve-Cylinder Motors. A—Duesenberg. B—Curtiss.
Fig. 139.—Counterbalanced Crank-Shafts Reduce Engine Vibration and Permit of Higher Rotative Speeds.
In some automobile engines, extremely good results have been secured in obtaining steady running with minimum vibration by counterbalancing the crank-shafts as outlined at Fig. 139. The shaft at A is a type suitable for a high speed four-cylinder vertical or an eight-cylinder Vee type. That at B is for a six-cylinder vertical or a twelve-cylinder V with scissors joint rods. If counterbalancing crank-shafts helps in an automobile engine, it should have advantages of some moment in airplane engines, even though the crank-shaft weight is greater.
BALL-BEARING CRANK-SHAFTS
While crank-shafts are usually supported in plain journals there seems to be a growing tendency of late to use anti-friction bearings of the ball type for their support. This is especially noticeable on block motors where but two main bearings are utilized. When ball bearings are selected with proper relation to the load which obtains they will give very satisfactory service. They permit the crank-shaft to turn with minimum friction, and if properly selected will never need adjustment. The front end is supported by a bearing which is clamped in such a manner that it will take a certain amount of load in a direction parallel to the axis of the shaft, while the rear end is so supported that the outer race of the bearing has a certain amount of axial freedom or “float.” The inner race or cone of each bearing is firmly clamped against shoulders on the crank-shaft. At the front end of the crank-shaft timing gear and a suitable check nut are used, while at the back end the bearing is clamped by a threaded retention member between the fly-wheel and a shoulder on the crank-shaft. The fly-wheel is held in place by a taper and key retention. The ball bearings are carried in a light housing of bronze or malleable iron, which in turn are held in the crank-case by bolts. The Renault engine uses ball bearings at front and rear ends of the crank-shaft, but has plain bearings around intermediate crank-shaft journals. The rotary engines of the Gnome, Le Rhone and Clerget forms would not be practical if ball bearings were not used as the bearing friction and consequent depreciation would be very high.
ENGINE-BASE CONSTRUCTION
One of the important parts of the power plant is the substantial casing or bed member, which is employed to support the cylinders and crank-shaft and which is attached directly to the fuselage engine supporting members. This will vary widely in form, but as a general thing it is an approximately cylindrical member which may be divided either vertically or horizontally in two or more parts. Airplane engine crank-cases are usually made of aluminum, a material which has about the same strength as cast iron, but which only weighs a third as much. In rare cases cast iron is employed, but is not favored by most engineers because of its brittle nature, great weight and low resistance to tensile stresses. Where exceptional strength is needed alloys of bronze may be used, and in some cases where engines are produced in large quantities a portion of the crank-case may be a sheet steel or aluminum stamping.
Fig. 140.—View of Thomas 135 Horse-Power Aeromotor, Model 8, Showing Conventional Method of Crank-Case Construction.
Crank-cases are always large enough to permit the crank-shaft and parts attached to it to turn inside and obviously its length is determined by the number of cylinders and their disposition. The crank-case of the radial cylinder or double-opposed cylinder engine would be substantially the same in length. That of a four-cylinder will vary in length with the method of casting the cylinder. When the four-cylinders are cast in one unit and a two-bearing crank-shaft is used, the crank-case is a very compact and short member. When a three-bearing crank-shaft is utilized and the cylinders are cast in pairs, the engine base is longer than it would be to support a block casting, but is shorter than one designed to sustain individual cylinder castings and a five-bearing crank-shaft. It is now common construction to cast an oil container integral with the bottom of the engine base and to draw the lubricating oil from it by means of a pump, as shown at Fig. 140. The arms by which the motor is supported in the fuselage are substantial-ribbed members cast integrally with the upper half.
Fig. 142.—Method of Constructing Eight-Cylinder Vee Engine, Possible if Aluminum Cylinder and Crank-Case Castings are Used.
The approved method of crank-case construction favored by the majority of engineers is shown at the top of Fig. 141, bottom side up. The upper half not only forms a bed for the cylinder but is used to hold the crank-shaft as well. In the illustration, the three-bearing boxes form part of the case, while the lower brasses are in the form of separately cast caps retained by suitable bolts. In the construction outlined the bottom part of the case serves merely as an oil container and a protection for the interior mechanism of the motor. The cylinders are held down by means of studs screwed into the crank-case top, as shown at Fig. 141, lower view. If the aluminum cylinder motor has any future, the method of construction outlined at Fig. 142, which has been used in cast iron for an automobile motor, might be used for an eight-cylinder Vee engine for airplane use. The simplicity of the crank-case needed for a revolving cylinder motor and its small weight can be well understood by examination of the illustration at Fig. 143, which shows the engine crank-case for the nine-cylinder “Monosoupape” Gnome engine. This consists of two accurately machined forgings held together by bolts as clearly indicated.
CHAPTER X
Power Plant Installation—Curtiss OX-2 Engine Mounting and Operating Rules—Standard S. A. E. Engine Bed Dimensions—Hall-Scott Engine Installation and Operation—Fuel System Rules—Ignition System—Water System—Preparations to Start Engine—Mounting Radial and Rotary Engines—Practical Hints to Locate Engine Troubles—All Engine Troubles Summarized—Location of Engine Troubles Made Easy.
The proper installation of the airplane power plant is more important than is generally supposed, as while these engines are usually well balanced and run with little vibration, it is necessary that they be securely anchored and that various connections to the auxiliary parts be carefully made in order to prevent breakage from vibration and that attendant risk of motor stoppage while in the air. The type of motor to be installed determines the method of installation to be followed. As a general rule six-cylinder vertical engine and eight-cylinder Vee type are mounted in substantially the same way. The radial, fixed cylinder forms and the radial, rotary cylinder Gnome and Le Rhone rotary types require an entirely different method of mounting. Some unconventional mountings have been devised, notably that shown at Fig. 144, which is a six-cylinder German engine that is installed in just the opposite way to that commonly followed. The inverted cylinder construction is not generally followed because even with pressure feed, dry crank-case type lubricating system there is considerable danger of over-lubrication and of oil collecting and carbonizing in the combustion chamber and gumming up the valve action much quicker than would be the case if the engine was operated in the conventional upright position. The reason for mounting an engine in this way is to obtain a lower center of gravity and also to make for more perfect streamlining of the front end of the fuselage in some cases. It is rather doubtful if this slight advantage will compensate for the disadvantages introduced by this unusual construction. It is not used to any extent now but is presented merely to show one of the possible systems of installing an airplane engine.
Fig. 145.—How Curtiss Model OX-2 Motor is Installed in Fuselage of Curtiss Tractor Biplane. Note Similarity of Mounting to Automobile Power Plant.
In a number of airplanes of the tractor-biplane type the power plant installation is not very much different than that which is found in automobile practice. The illustration at Fig. 145 is a very clear representation of the method of mounting the Curtiss eight-cylinder 90 H. P. or model OX-2 engine in the fuselage of the Curtiss JN-4 tractor biplane which is so generally used in the United States as a training machine. It will be observed that the fuel tank is mounted under a cowl directly behind the motor and that it feeds the carburetor by means of a flexible fuel pipe. As the tank is mounted higher than the carburetor, it will feed that member by gravity. The radiator is mounted at the front end of the fuselage and connected to the water piping on the motor by the usual rubber hose connections. An oil pan is placed under the engine and the top is covered with a hood just as in motor car practice. The panels of aluminum are attached to the sides of the fuselage and are supplied with doors which open and provide access to the carburetor, oil-gauge and other parts of the motor requiring inspection. The complete installation with the power plant enclosed is given at Fig. 146, and in this it will be observed that the exhaust pipes are connected to discharge members that lead the gases above the top plane. In the engine shown at Fig. 145 the exhaust flows directly into the air at the sides of the machine through short pipes bolted to the exhaust gas outlet ports. The installation of the radiator just back of the tractor screw insures that adequate cooling will be obtained because of the rapid air flow due to the propeller slip stream.
Fig. 146.—Latest Model of Curtiss JN-4 Training Machine, Showing Thorough Enclosure of Power Plant and Method of Disposing of the Exhaust Gases.
Fig. 147.—Front View of L. W. F. Tractor Biplane Fuselage, Showing Method of Installing Thomas Aeromotor and Method of Disposing of Exhaust Gases.
INSTALLATION OF CURTISS OX-2 ENGINE
The following instructions are given in the Curtiss Instruction Book for installing the OX-2 engine and preparing it for flights, and taken in connection with the very clear illustration presented no difficulty should be experienced in understanding the proper installation, and mounting of this power plant. The bearers or beds should be 2 inches wide by 3 inches deep, preferably of laminated hard wood, and placed 115⁄8 inches apart. They must be well braced. The six arms of the base of the motor are drilled for 3⁄8-inch bolts, and none but this size should he used.
1. Anchoring the Motor. Put the bolts in from the bottom, with a large washer under the head of each so the head cannot cut into the wood. On every bolt use a castellated nut and a cotter pin, or an ordinary nut and a lock washer, so the bolt will not work loose. Always set motor in place and fasten before attaching any auxiliary apparatus, such as carburetor, etc.
2. Inspecting the Ignition-Switch Wires. The wires leading from the ignition switch must be properly connected—one end to the motor body for ground, and the other end to the post on the breaker box of the magneto.
3. Filling the Radiator. Be sure that the water from the radiator fills the cylinder jackets. Pockets of air may remain in the cylinder jackets even though the radiator may appear full. Turn the motor over a few times by hand after filling the radiator, and then add more water if the radiator will take it. The air pockets, if allowed to remain, may cause overheating and develop serious trouble when the motor is running.
4. Filling the Oil Reservoir. Oil is admitted into the crank-case through the breather tube at the rear. It is well to strain all oil put into the crank-case. In filling the oil reservoir be sure to turn the handle on the oil sight-gauge till it is at right angles with the gauge. The oil sight-gauge is on the side of the lower half of the crank-case. Put in about 3 gallons of the best obtainable oil, Mobile B recommended. It is important to remember that the very best oil is none too good.
5. Oiling Exposed Moving Parts. Oil all rocker-arm bearings before each flight. A little oil should be applied where the push rods pass through the stirrup straps.
6. Filling the Gasoline Tanks. Be certain that all connections in the gasoline system are tight.
7. Turning on the Gasoline. Open the cock leading from the gasoline tank to the carburetor.
8. Charging the Cylinders. With the ignition switch OFF, prime the motor by squirting a little gasoline in each exhaust port and then turn the propeller backward two revolutions. Never open the exhaust valve by operating the rocker-arm by hand, as the push-rod is liable to come out of its socket in the cam follower and bend the rocker-arm when the motor turns over.
9. Starting the Motor by Hand. Always retard the spark part way, to prevent back-firing, by pulling forward the wire attached to the breaker box. Failure to so retard the spark in starting may result in serious injury to the operator. Turn on the ignition switch with throttle partly open; give a quick, strong pull down and outward on the starting crank or propeller. As soon as the motor is started advance the spark by releasing the retard wire.
10. Oil Circulation. Let the motor run at low speed for a few minutes in order to establish oil circulation in all bearings. With all parts functioning properly, the throttle may be opened gradually for warming up before flight.
STANDARD S.A.E. ENGINE BED DIMENSIONS
The Society of Automotive Engineers have made efforts to standardize dimensions of bed timbers for supporting power plant in an aeroplane. Owing to the great difference in length no standardization is thought possible in this regard. The dimensions recommended are as follows:
| Distance between timbers | 12 | in. | 14 | in. | 16 | in. | ||
| Width of bed timbers | 1 | 1⁄2 | in. | 1 | 3⁄4 | in. | 2 | in. |
| Distance between centers of bolts | 13 | 1⁄2 | in. | 15 | 3⁄4 | in. | 18 | in. |
It will be evident that if any standard of this nature were adopted by engine builders that the designers of fuselage could easily arrange their bed timbers to conform to these dimensions, whereas it would be difficult to have them adhere to any standard longitudinal dimensions which are much more easily varied in fuselages than the transverse dimensions are. It, however, should be possible to standardize the longitudinal positions of the holding down bolts as the engine designer would still be able to allow himself considerable space fore-and-aft of the bolts.
HALL-SCOTT ENGINE INSTALLATION
Fig. 149.—Plan and Side Elevation of Hall-Scott A-7 Four-Cylinder Airplane Engine, with Installation Dimensions.
The very thorough manner in which installation diagrams are prepared by the leading engine makers leaves nothing to the imagination. The dimensions of the Hall-Scott four-cylinder airplane engine are given clearly in our inch measurements with the metric equivalents at Figs. 148 and 149, the former showing a vertical elevation while the latter has a plan view and side elevation. The installation of this engine in airplanes is clearly shown at Figs. 150 and 151, the former having the radiator installed at the front of the motor and having all exhaust pipes joined to one common discharge funnel, which deflects the gas over the top plane while the latter has the radiator placed vertically above the motor at the back end and has a direct exhaust gas discharge to the air.
CENSORED
CENSORED
The dimensions of the six-cylinder Hall-Scott motor which is known as the type A-5 125 H. P. are given at Fig. 152, which is an end sectional elevation, and at Fig. 153, which is a plan view. The dimensions are given both in inch sizes and the metric equivalents. The appearance of a Hall-Scott six-cylinder engine installed in a fuselage is given at Fig. 154, while a diagram showing the location of the engine and the various pipes leading to the auxiliary groups is outlined at Fig. 155. The following instructions for installing the Hall-Scott power plant are reproduced from the instruction book issued by the maker. Operating instructions which are given should enable any good mechanic to make a proper installation and to keep the engine in good running condition.
CENSORED
Fig. 153.—Plan View of Hall-Scott Type A-5 125 Horse-Power Airplane Engine, Showing Installation Dimensions.
Fig. 154.—Three-Quarter View of Hall-Scott Type A-5 125 Horse-Power Six-Cylinder Engine, with One of the Side Radiators Removed to Show Installation in Standard Fuselage.
Fig. 155.—Diagram Showing Proper Installation of Hall-Scott Type A-5 125 Horse-Power Engine with Pressure Feed Fuel Supply System.
FUEL SYSTEM INSTALLATION
Gasoline giving the best results with this equipment is as follows: Gravity 58-62 deg. Baume A. Initial boiling point—Richmond method—102° Fahr. Sulphur .014. Calorimetric bomb test 20610 B. T. U. per pound. If the gasoline tank is placed in the fuselage below the level of the carburetor, a hand pump must be used to maintain air pressure in gas tank to force the gasoline to the carburetor. After starting the engine the small auxiliary air pump upon the engine will maintain sufficient pressure. A-7a and A-5a engines are furnished with a new type auxiliary air pump. This should be frequently oiled and care taken so no grit or sand will enter which might lodge between the valve and its seat, which would make it fail to operate properly. An air relief valve is furnished with each engine. It should be screwed into the gas tank and properly regulated to maintain the pressure required. This is done by screwing the ratchet on top either up or down. If two tanks are used in a plane one should be installed in each tank. All air pump lines should be carefully gone over quite frequently to ascertain if they are tight. Check valves have to be placed in these lines. In some cases the gasoline tank is placed above the engine, allowing it to drain by gravity to the carburetor. When using this system there should be a drop of not less than two feet from the lowest portion of the gasoline tank to the upper part of the carburetor float chamber. Even this height might not be sufficient to maintain the proper volume of gasoline to the carburetor at high speeds. Air pressure is advised upon all tanks to insure the proper supply of gasoline. When using gravity feed without air pressure be sure to vent the tank to allow circulation of air. If gravity tank is used and the engine runs satisfactorily at low speeds but cuts out at high speeds the trouble is undoubtedly due to insufficient height of the tank above the carburetor. The tank should be raised or air pressure system used.
IGNITION SWITCHES
Two “DIXIE” switches are furnished with each engine. Both of these should be installed in the pilot’s seat, one controlling the R. H., and the other the L. H. magneto. By shorting either one or the other it can be quickly determined if both magnetos, with their respective spark-plugs, are working correctly. Care should be taken not to use spark-plugs having special extensions or long protruding points. Plugs giving best results are extremely small with short points.
WATER SYSTEMS
A temperature gauge should be installed in the water pipe, coming directly from the cylinder nearest the propeller (note illustration above). This instrument installed in the radiator cap has not always given satisfactory results. This is especially noticeable when the water in the radiator becomes low, not allowing it to touch the bulb on the moto-meter. For ordinary running, it should not indicate over 150 degrees Fahr. In climbing tests, however, a temperature of 160 degrees Fahr. can be maintained without any ill effects upon the engine. In case the engine becomes overheated, the indicator will register above 180 degrees Fahr., in which case it should be stopped immediately. Overheating is most generally caused by retarded spark, excessive carbon in the cylinders, insufficient lubrication, improperly timed valves, lack of water, clogging of water system in any way which would obstruct the free circulation of the water.
Overheating will cause the engine to knock, with possible damaging results. Suction pipes should be made out of thin tubing, and run within a quarter or an eighth of an inch of each other, so that when a hose is placed over the two, it will not be possible to suck together. This is often the case when a long rubber hose is used, which causes overheating. Radiators should be flushed out and cleaned thoroughly quite often. A dirty radiator may cause overheating.
When filling the radiator it is very important to remove the plug on top of the water pump until water appears. This is to avoid air pockets being formed in the circulating system, which might not only heat up the engine, but cause considerable damage. All water pump hoses and connections should be tightly taped and shellacked after the engine is properly installed in the plane. The greatest care should be taken when making engine installation not to use smaller inside diameter hose connection than water pump suction end casting. One inch and a quarter inside diameter should be used on A-7 and A-5 motors, while nothing less than one inch and a half inside diameter hose or tubing on all A-7a and A-5a engines. It is further important to have light spun tubing, void of any sharp turns, leads from pump to radiator and cylinder water outlet to radiator. In other words, the water circulation through the engine must be as little restricted as possible. Be sure no light hose is used, that will often suck together when engine is started. To thoroughly drain the water from the entire system, open the drain cock at the lowest side of the water pump.
PREPARATIONS TO START ENGINE
Always replenish gasoline tanks through a strainer which is clean. This strainer must catch all water and other impurities in the gasoline. Pour at least three gallons of fresh oil into the lower crank-case. Oil all rocker arms through oilers upon rocker arm housing caps. Be sure radiators are filled within one inch of the top.
After all the parts are oiled, and the tanks filled, the following must be looked after before starting: See if crank-shaft flange is tight on shaft. See if propeller bolts are tight and evenly drawn up. See if propeller bolts are wired. See if propeller is trued up to within 1⁄8′′.
Every four days the magnetos should be oiled if the engine is in daily use.
Every month all cylinder hold-down nuts should be gone over to ascertain if they are tight. (Be sure to recotter nuts.)
See if magnetos are bolted on tight and wired.
See if magneto cables are in good condition.
See if rocker arm tappets have a .020′′ clearance from valve stem when valve is seated.
See if tappet clamp screws are tight and cottered.
See if all gasoline, oil, water pipes and connections are in perfect condition.
Air on gas line should be tested for leaks.
Pump at least three pounds air pressure into gasoline tank.
After making sure that above rules have been observed, test compression of cylinders by turning propeller.
“DO NOT FORGET TO SHORT BOTH MAGNETOS”
Be sure all compression release and priming cocks do not leak compression. If they do, replace same with a new one immediately, as this might cause premature firing.
Open priming cocks and squirt some gasoline into each.
Close cocks.
Open compression release cocks.
Open throttle slightly.
If using Berling magnetos they should be three-quarters advanced.
If all the foregoing directions have been carefully followed, the engine is ready for starting.
In cranking engine either by starting crank, or propeller, it is essential to throw it over compression quickly.
Immediately upon starting, close compression release cocks.
When engine is running, advance magnetos.
After it has warmed up, short one magneto and then the other, to be sure both magnetos and spark-plugs are firing properly. If there is a miss, the fouled plug must be located and cleaned. There is a possibility that the jets in the carburetor are stopped up. If this is the case, do not attempt to clean same with any sharp instrument. If this is done, it might change the opening in the jets, thus spoiling the adjustment. Jets and nozzles should be blown out with air or steam.
An open intake or exhaust valve, which might have become sluggish or stuck from carbon, might cause trouble. Be sure to remedy this at once by using a little coal-oil or kerosene on same, working the valve by hand until it becomes free. We recommend using graphite on valve stems mixed with oil to guard against sticking or undue wear.