Carl H. Clark

II. Two Cycle Engines.

The ordinary type of two cycle engine is illustrated in Fig. 8. A is the cyliuder of cast iron, in which travels the piston P. The piston is shown in its lowest position, its highest position being at a. It will be noted that from a point just below a the bore of the cylinder is slightly increased; this is termed the counterbore and is for the purpose of allowing the pis-

Construction And Management Of Gasoline Engines 194

Fig. 8.

ton to over run the edge of the working part of the cylinder bore and prevent it from forming a shoulder at the upper end of its stroke as the bore wears. There is a considerable space above a, which is called the compression space, for compressing the gas, as before explained.

The cylinder is surrounded by the water jacket j through which water is circulated to carry off the excess of heat which is generated in the cylinder and which would otherwise cause the cylinder to become overheated and perhaps injured. The jacket surrounds the cylinder and sometimes the exhaust pipe, and extends well below the lower end of the bore.

II is the cylinder head, which is also hollow for water circulation, except in the small sizes. The head is held in place by the bolts or studs ss; the joint between the cylinder and the cover is filled by a thin sheet of packing to make it gas tight. The studs are from four to six in number. The water enters the jacket at e, and circulates around the cylinder and cover and passes out at f. It passes from the cylinder jacket to the head through the outside pipe, as shown, or through an opening directly upwards between the studs. The former method is preferable, as when the opening is cut in the packing there is liability of leak-

Construction And Management Of Gasoline Engines 195

Fig. 9.

age and of water being drawn into the cyliuder. Many engines have the cylinders and heads cast together, thus avoiding the joint; this saves all trouble with the circulating water and allows a rather more symmetrical head. It is, however, harder to examine and repair, as the cylinder, and sometimes a portion of the base, must be lifted to get at the working parts.

P is the piston; r the piston rings, usually three in number, which are set into grooves in the piston. They are turned to a diameter slightly larger than that of the cylinder and are sprung in, so that they press out against the walls of the cylinder and prevent leakage past the piston. The piston itself is a rather loose fit in the cylinder, and the rings are depended upon for tightness. Two of the rings are placed at the top of the piston, and the other one at the lower edge; this is to prevent leakage from one part to another. For example, when the piston is a part of the way down the gas in the base might be forced up past the piston and out of the exhaust port, were it not for this lower ring. The joints in the rings are shown halved; they are often simply cut across at an angle; the former is the preferable method, as there is no chance for leakage. Piston and rings are of cast iron.

Wis the wrist pin, or pivot, upon which the connecting rod swings; this pin may either be fast in the rod and turn in the piston, or vice versa, being held in place by a set screw. In some cases it is left entirely free to turn in both, but this is hardly advisable, as there is a chance of the end of the pin scoring the bore of the cylinder. The wrist pin is of steel.

Construction And Management Of Gasoline Engines 196

Fig. 10.

C is the connecting rod, of either steel or bronze; when of the latter metal, no inserted boxes are necessary, as the bronze and the steel pins will wear well together. The upper end of the rod consists simply of an eye, through which the wrist pin is inserted. The lower or crank pin end is cut, and the under portion of the bearing is fastened on with two bolts g; this is necessary in order to get it into place, and to allow a chance of adjustment to take up wear.

SS is the crank shaft, which should be made of the best of steel, as it is, perhaps, the most important part of the engine; the part encircled by the lower end of the connecting rod is called the crank. On the end of the crankshaft is the flywheel F, of cast iron ; it is held in place by a key It, which is of rectangular section and is sunk half in the shaft and half in the hub of the flywheel, and prevents the flywheel turning on the shaft. The handle i,for use in starting the motor, is contained in a hole in the rim of the flywheel and is pulled out for use. It is encircled by a spring, which draws it in when it is released, and prevents injury to the operator.

The sleeves of composition b b which are inserted in the casting of the base, make a good bearing for the shaft. They not only make a better bearing than the cast iron of the base, but also allow of the insertion of new sleeves after wear has taken place.

P is the water pump, for circulating the water in the jacket: it is of the usual type of plunger pump, consisting of the plunger L working in the barrel. The plunger is made tight at the upper end of the barrel by the packing gland as shown, and at the lower end of the barrel are the usual two foot valves. The water is drawn in through one valve by the upward strokes, each valve allowing the water to pass in one direction only. The pump is operated by the eccentric L on the crank shaft, and the eccentric strap If, so that the pump has a stroke for each stroke of the piston.

Construction And Management Of Gasoline Engines 197

Fig. 11.

The thrust bearing, shown at X, takes up the forward thrust of the propeller and prevents the crankshaft being forced against the forward bearing by the pressure. It consists essentially of two hardened steel rings with steel balls running between them; the balls are held in a thin plate of composition and revolve freely.

N is the coupling by which the engine shaft is connected to the propeller shaft; it is a sleeve of cast iron, fastened to the shafts with set screws or keys.

At d is a pet cock, leading from the water jacket into the aa'; its purpose is to drain the water out of the jacket in cold weather, as the formation of the jacket is liable to split the casting. The opening at t also leads into the air and is provided with a pet cock for the purpose of relieving the compression when turning the engine over by hand.

I is the igniting mechanism, which will be described later.

G is a grease cup for lubricating the crankshaft bearing, a similar one being fitted to the forward bearing; it consists of a sort of cylindrical box with a screw and cover and a stem leading down to the bearing. It is filled with grease, which is forced into the bearing by screwing down the cover. It is advisable to use the grease in these bearings, as it is thick and forms a film between the shaft and the bearing, which prevents leakage from the crank case.

At O is a lubricator for oiling the cylinder and piston ; it may be considered simply as an oil reservoir for the present, as it will be described in detail later. The oil is delivered upon the bore of the cylinder and is distributed by the piston. The wrist pin is oiled by an axial hole, through which oil is received from the cylinder walls and delivered to the wrist pin. As a matter of fact, the wrist pin requires little lubrication, as the movement of the bearing around it is slight, otherwise the lubrication received in this way would not be sufficient. On the lower end of the connecting rod at y, is a small scoop, with a hole above it leading into the crank-pin bearing; the base is partially filled with oil. and a small amount is scooped up on each revolution and delivered to the crank-pin bearing.

Construction And Management Of Gasoline Engines 198

Fig. 12.

Fig. 9-10-11 represent the outlines of three standard makes of engine. In Fig. 9 the cylinder and upper portion of the base are in one casting, the lower part of the base and the cylinder cover being separate. At nis a removable cover over a hand hole leading into the base, allowing examination and adjustment of the crank-pin bearing. The gasoline vapor is delivered into the base through an opening in the cover plate N from the vaporizer V which will be described in detail later. The connection for the exhaust pipe is at E, on the rear of the engine. The water pump is just back of the flywheel and delivers water to the jacket through the pipe e; the water passes out of the jacket at f".

Tis the compression cock, and d is the drain cock for draining the jacket. At O is the oil cup for oiling the piston and at o is cup and cock for introducing oil into the base.

I is the igniting gear, which will be explained in another chapter.

Fig. 10 is of the same general type, the letters referring to the same parts. In this type the cylinder and entire base are one casting, the main bearings being held in plates bolted on front and rear of the base. The water-pump and igniter in this case are on the rear of the engine, the pump drawing water from the outside through the pipe ft, and discharging through the pipe e into the jacket; the cooling water flows out at Faf-ter circulating over the cylinder cover. GG are the grease cups for the main journals. L is the eccentric for operating the pump. XXate the flanges by which the engine is bolted in place.

Fig. 11 is of the type having cylinder and bead in one casting. The upper part of the base is a separate casting bolting on to the cylinder at Z; the lower part of the base bolts on below. The pump is horizontal, directly behind the flywheel, and discharges into the jacket through the pipe shown, n is the ball-thrust bearing, and r is the shaft coupling. F is the cooling water outlet, and E the exhaust outlet, as before. No igniter gear is shown, as with one method of ignition none is required.

While no two makes of motor have the same parts in exactly the same place, the above description should enable the reader to become familiar with the various working parts and the attachments, as all must have these parts in some form or other.