CARL H. CLARK
Fig. 13 represents a section of a four-cycle engine of a common type. The working parts are very similar to those of the two-cycle type, but are further complicated by the addition of the valves and the means for controlling them. The piston, connecting rod and crank shaft remain as in the other type. The valves are controlled from the two lateral shafts A and B, which are run from the main shaft through the gears c d e. Since each valve only opens once for each two revolutions of the engine, the lateral shafts or cam shafts, as they are termed, must revolve only half as
fast as the main shaft. For this reason the gear d, on the main shaft is only half as large as those on the two cam shafts. These cam shafts .run in bearings in the base, and carry small cams or tappets, which strike the lower ends of the stems at the proper time and thus raise the valve from the seat. F is the admission chamber opening into the cylinder above the valve f-. G is the exhaust chamber containing the exhaust valve (j.
The valves have stems extending down through the casing in bearings to a point where they can be raised by the cam. The lower part of each stem is made square as shown, to form a guide, and the lower end is provided with a roller r, to reduce the friction. The square portion may be made a separate piece, with the valve stem just resting upon it; this facilitates the removal of the valves and stems, as the square guiding part will remain in place. At ssarecoiled springs on the valve
spindles to return the valves after being raised by the cams. At k k directly above the valves are plugs, either bolted or threaded in place, which, when removed, allow the examination or removal of the valves.
The cylinder and head is surrounded by the usual water jacket, j, which also, as far as possible, surrounds the valve chests. In the particular style shown the head is cast with the cylinder, but it may equally well have the bolted head. The base in this type is made more ample and easier of access, as size is of little moment, and it Is not necessary that it should be air tight. The sides of the base are covered with plates to keep out dirt and prevent the splashing of oil. I is the admission port where the vaporizing device is attached, and E is the exhaust opening for the connection of the exhaust piping.
The sparking device is located at X and the engine is also provided with the usual compression cock, lubricator drain cocks, etc., as before described.
The devices for timing the electric igniting spark and driving the pump are also controlled from the cam shaft.
The long sleeve tube bearing around the valve stem at n is provided to form a guide for the stem, and also prevent the escape of the gas from the chamber out along the rod.
The sides of the base are enclosed by plates which may be easily removed for examination, exposing the entire base. These plates are swelled out around the cams and rollers.
The gears c, d, e, are usually placed c the front of the engine with the gear d on the man shaft just behind the flywheel and the others just outside the main casing; they are then provided with a separate casing.
Referring back to Fig. 4 it will be plain that the suction of the piston on its down strake will have a tendency to raise the inlet valve and allow the admission of gas. It is thus evident that is not entirely necessary that the inlet valve should be mechanically controlled, but may be left to be operated by the auction of the piston. The exhaust valve, however, as will be seen by referring to Fig. 7, must be raised against the pressure in the cylinder, so that it must be mechanically operated. Fig. 14 shows the relative location of the valves when this arrangementis adopted.
lis the inlet opening, f is the inlet valve, inverted in this case and held in place by the coiled spring s, although, of course the pressure in the cylinder will tend to hold it and press it closer against its seat; y is the exhaust valve, as before. This arrangement may be either on the side or the ends of the engines. This arrangementis, of course, simpler, as it dispenses with one cam shaft, and the accompanying gear. The question as to whether both valves should be mechanically operated, is much disputed at present, the representative builders being divided upon it in practice. It may be said, however, that while for slow or medium turning engines the suction inlet valve works well, for high speed engines the mechanically controlled inlet valve is preferred, as it acts quicker and more regularly.
Fig. 15 shows a very common arrangement for single cylinder engines; the valves are on the back of the engines. The exhaust valve is operated by the short cam shaft a, which is driven by the gears, c d, the gear at d being, of course, half the size of c. The inlet valve is operated by suction. To get at the valves the poition of the casting containing the inlet valve is removable, thus making both valves accessible.
The flywheel, crankshaft and connecting-rod are of the same type as those already discussed, with the exception that the cranks are extended across the shaft and are broadened out to form counterbalances, to partially balance the weight of the crank pin and connecting rod, thus somewhat lessening the vibration.
The cam shaft is at a and is driven by the two gears, c and d. The exhaust valve G is actuated by the roller r and cam / on the cam shaft a. The inlet valve F is held up in place by the spring S. The inlet port leads in above the inlet valve; E is the exhaust outlet. The igniter gear iV is also actuated by the cam shaft. At P is the cooling water pump, run from the eccentric e. The ball thrust bearing is at n. The coupling X, in this case is of the flanged type, the propeller shaft be-iug furnished with a similar coupling, the two being held together by bolts through the flanges, each part of the coupling being fastened to its shaft by set screws or keys.
It will be noted that the cylinder, valve chest and base are a single casting, the head being bolted on, and the main bearings being contained in separate flanged castings bolted on to the sides of the base. The flange for bolting the engine to the bed, in this particular engine, is at the extreme bottom of the base, instead of about at the line of the shaft. The cylinder and valve chest are surrounded with the usual water jacket j. A grease cup gg is for lubricating the main bearings. The cylinder is provided with the usual compression cock and oil cup, which are not shown.
The gears c, d being inside the base, are well lubricated by the splashing of the oil by the cranks, and are less noisy than when outside the casing. The sides of the base are provided with round hand hole plates, a portion of which is shown.
Two views of a representative small motor are given in Figs. 16 and 17. The cam shaft is located at a and is driven by the gears which are shown just in the rear of the flywheel. At c is the cam and roller which actuates the exhaust valve. The cam consists of a collar with a flat projection or toe upon its surface; the roller rests just above the surface of the collar, and is forced upwards by being struck by the projection. The roller is inserted to lessen the friction by rolling instead of rubbing. The valve stem extends upward into the valve chamber, and is encircled by the coiled springe; the stem is guided by the guide at g. The exhaust is at E; 7 is the pipe leading from the vaporizer V to the inlet port in the valve chest. The inlet valve is directly below the spring S and is inverted, being held in place by the spring. The dome shaped cap containing the inlet valve is removable for access to both valves. The complete cover is also removable.
It will be observed that this engine has an open frame very similar to that of a steam engine, giving free access to the crank-pin and main bearings; the latter are shown fitted with oil boxes b instead of the grease cups, as there is no pressure tending to force the oil out along the shaft as in the two-cycle type. This open base not only makes the bearings, more accessible, but also renders it easier to lubricate them and keep them cool. At H is the ignition gear P is the cooling water-pump, run by the eccentric e The suction is piped to d and the pump discharges through the pipe k into the cylinder. The outlet for the cooling water is at O; N is the cylinder oil cup tor oiling the bore of the cylinder. The compression cock R is for relieving the compression at starting. The coupling at X is for attaching the propeller shaft.
In this engine the cylinder, base and bolting flange are one casting, the upper half of the main bearings being removable for the insertion of the shaft. The cover is bolted en separately.
An engine of the light high-speed type, is shown in Fig. 18. The cylinder and valve chest are a single casting bolti: g on to the upper part of the base.