The growth of the automobile industry has seen the transformation of the automobile motor from a single-cylinder engine to one having a number of individually cast cylinders, and later to one with a number of cylinders within a single block. It has also witnessed a long struggle for supremacy of certain ideas, with reference to the general design of the cylinder blocks.
There is a rather constant discussion about the advantages of the several types of blocks which are characterized by the several letters resembled, more or less, by the cross sections of the cylinder blocks. These are the T-, L-, I-, and F-head engines. Some relative statements of engineering conclusions with reference to the various types are given in the following.
The engine is of 1910 vintage and is a typical example of early T-head practice. Gas and air enter at one port, pass the intake valve, are compressed and fired, and the burned gases are driven off past the other valve and through the port on the opposite side of the T-head. Two camshafts and two camshaft drive gears are needed. Combustion or flame propagation may be slower, because of the distance to travel and spaces to fill before the piston is driven down. Sometimes two plugs per cylinder and double ignition are used to speed up flame propagation.
As a matter of fact, the L is a reversed one, as may be seen in studying the illustrations. In this design all valves, cams, valve lifters, and other moving parts are inclosed in the crankcase, and oiling is thus made easy.
Valve-in-head is a term commonly applied to the I-head motor. Overhead valve is another term equally descriptive. A cross section of an overhead-valve or valve-in-head motor resembles a straight line or the letter I. A valve-inhead motor stands a bit higher than a motor with the valves in the cylinder block. The cylinder block is narrower, and as a rule projects, on either side, about an equal distance from the cylinder bore. Usually a sheet-metal cover is provided to protect the valve mechanism from dust and dirt, and to prevent loss of oil. Lubrication is more uniform with the cover. In most cases, push rods used to operate the rocker arms are housed back of a metal plate used to exclude dirt and retain oil.
The F-head engine is a combination of the I-head and the L-head types. The usual practice is to place intake valves overhead, and the exhaust valves in the cylinder block. Exhaust valves lift directly on the valve lifters. Intake valves are operated by push rods and rocker arms. This arrangement of valves is one of the best possible insofar as valve areas and power are concerned. Engines of this type are sometimes used for racing cars. Practically the same amount of room is available for valves as is the case in the T-head motor.
Along with the attempt to secure motors which are flexible, came the practice of increasing the number of cylinders. This led to the perfection of the V-type motor where two rows or banks of cylinders are arranged in V form. The centre of the crankshaft is at the point of the V. Two connecting rods may be hooked side by side to one throw of the crankshaft.