Fig. 24.—Single-acting engines.
Fig. 25.—Engine with inclined bearings.
The Frame.—Gas-engines driven as they are, by explosions, giving rise to shocks and blows, should be built with frames, heavy, substantial, and broad-based,
so as to rest solidly on the ground. This essential condition is often fulfilled at the cost of the engine's appearance; but appearance will be willingly sacrificed to meet one of the requirements of perfect operation. For engines of more than 8 to 10 horse-power, frames should be employed which can be secured to the masonry foundation without a separate pedestal or base. Some manufacturers, for the purpose of lightening the frame, attach but little importance to the foundation and to strength of construction, and employ the design illustrated in place of the crank-shaft bearing (Fig. 25); others, in order to facilitate the adjusting of the connecting-rod bearings, prefer the second form (Fig. 26). It is evident that, in the first case, a part of the effort produced by the explosion reacts on the upper portion of the connecting-rod bearing, on the cap of the crank-shaft bearing, and consequently on the fastening-bolts. In the second case, if the adjustment be not very carefully made, or if the rubbing surfaces are insufficient, the entire thrust due to the explosion
will be received by the meeting parts of the two bushings, thus injuring them and causing a more rapid wear. In the construction of large engines, some manufacturers take the precaution of forming the connecting-rod bearings of four parts, adjustable to take up the wear, so that the effort is exerted against the parts disposed at right angles to each other. A form that seems rational is that shown in Fig. 27, in which the reaction of the thrust is taken up by the lower bearing, rigidly supported by the braced frame, in the direction opposite to that of the explosive effort.
Fig. 26.—Engine with straight bearings.
