As in nearly all types of low compression, or carbureting oil engines, the Rumely engine receives an injection of water in the cylinder to aid the combustion and cooling, and to reduce the initial pressure of the explosion. While the initial pressure is reduced by the water vapor, and with it the strain on the engine, the mean effective pressure is increased because of the absorption of heat from the walls and the more perfect combustion. The only moving part in the carburetor is a single plate controlled by the governor which is produced with one or more air passages. The governor that operates this valve is driven by gears and regulates the speed by throttling the charge. The speed of the engine can be varied from 300 to 400 revolutions per minute while the engine is running. [Illustration: Fig. 129. Higgins Oil Carburetor. ] In this engine it is a very simple matter to remove the crank-case cover and the cylinder heads and expose the whole of the working mechanism of the engine. After removing the cylinder heads and without changing his position, the operator can examine, clean, and, if necessary, regrind the valves. Also without changing position the operator can control his reverse transmission gears, friction clutch for starting the tractor. He is also in reach of the ignition apparatus, governor carburetor and oiler. The crank case is cast in one piece. The bearings are cast integral with the crank case, and are fitted with interchangeable, adjustable, babbitted shells. Binder caps hold the bearings together and keep the babbitted shells securely in position. The design permits removal of binder caps for examination of crank shaft bearings without distributing the adjustment. The crank case is secured to tractor frame by well fitted bolts, thereby avoiding annoyance from loose bolts and nuts. The crank case is covered with a sheet steel lid that shuts out all dust and dirt. This cover can easily be removed at any time by simply unscrewing the bolts that hold it in place. It is constructed with this cover on top instead of on the side or end, which permits of easy access to any working parts in the crank case. [Illustration: Fig. 130. Rumely Oil Pull Tractor. ] To further facilitate the accessibility to working parts in the crank case, a secondary cover is provided which can be removed in a couple of minutes. This opening is large enough to allow the operator to reach any point within the crank case. All cams are key-seated upon the cam shaft with double key-seats, which absolutely prevent any possibility of slipping or alteration in the timing of the engine. The exhaust and intake valves are mechanically operated. The valves are constructed with steel stem, nickel-steel heads, the whole being highly finished.