This plug will be furnished either with or without the finned portion, to meet individual requirements. The manufacturers lay special stress upon the simplicity of construction and upon the method of clamping, which is claimed to make the plug absolutely gas-tight.
CHAPTER VII
[Why Lubrication Is Necessary]—[Friction Defined]—[Theory of Lubrication]—[Derivation of Lubricants]—[Properties of Cylinder Oils]—[Factors Influencing Lubrication System Selection]—[Gnome Type Engines Use Castor Oil]—[Hall-Scott Lubrication System]—[Oil Supply by Constant Level Splash System]—[Dry Crank-Case System Best for Airplane Engines]—[Why Cooling Systems Are Necessary]—[Cooling Systems Generally Applied]—[Cooling by Positive Pump Circulation]—[Thermo-Syphon System]—[Direct Air-Cooling Methods]—[Air-Cooled Engine Design Considerations].
WHY LUBRICATION IS NECESSARY
The importance of minimizing friction at the various bearing surfaces of machines to secure mechanical efficiency is fully recognized by all mechanics, and proper lubricity of all parts of the mechanism is a very essential factor upon which the durability and successful operation of the motor car power plant depends. All of the moving members of the engine which are in contact with other portions, whether the motion is continuous or intermittent, of high or low velocity, or of rectilinear or continued rotary nature, should be provided with an adequate supply of oil. No other assemblage of mechanism is operated under conditions which are so much to its disadvantage as the motor car, and the tendency is toward a simplification of oiling methods so that the supply will be ample and automatically applied to the points needing it.
In all machinery in motion the members which are in contact have a tendency to stick to each other, and the very minute projections which exist on even the smoothest of surfaces would have a tendency to cling or adhere to each other if the surfaces were not kept apart by some elastic and unctuous substance. This will flow or spread out over the surfaces and smooth out the inequalities existing which tend to produce heat and retard motion of the pieces relative to each other.
A general impression which obtains is that well machined surfaces are smooth, but while they are apparently free from roughness, and no projections are visible to the naked eye, any smooth bearing surface, even if very carefully ground, will have a rough appearance if examined with a magnifying glass. An exaggerated condition to illustrate this point is shown at [Fig. 75]. The amount of friction will vary in proportion to the pressure on the surfaces in contact and will augment as the loads increase; the rougher surfaces will have more friction than smoother ones and soft bodies will produce more friction than hard substances.