By Courtesy of the Brooks Boat Mfg, Co.

Most manufacturers of these motors claim that theirs is the best, most reliable motor on the market, and in support of this claim give a detailed description of the different parts and manner of construction; explain the principle upon which the motor operates; show illustrations of the different parts, etc.

All this would be perfectly proper and of value to those seeking information were it not inferred that each point and principle described was a special feature of their particular motor and of no other. To those unfamiliar with them, this result is a confused idea that there are numerous kinds of these motors involving entirely different principles of construction and operation. It is with a view to correct this erroneous impression and at the same time give a true understanding of the principle and operation of all gasoline motors that the following explanation is given. The subject is therefore taken up only in a general sense and does not apply to motors of one make any more than it does to those of another.

Properties Of Gasoline

Gasoline alone will ignite but not explode. The mixture of vapor formed by gasoline and air will ignite and explode. When this vapor is compressed it will ignite easier and give more power to the explosion. The power of all gasoline motors is derived from the impulse given by the explosion of the compressed vapor.

Motor Construction

Marine gasoline motors consist of one or more water jacketed cylinders with an immovable head at the top end, and a movable piston inside that is connected by a rod to the crank shaft. This is the foundation of all motors.

The conditions are that in operation the combustion of the vapor produces heat; that the cylinder must be kept cool for proper lubrication; that a proper mixture of vapor must be supplied to the cylinder; that this vapor must be compressed by the piston; that the compressed vapor must be ignited; that proper lubrication to all parts must be had, an that all of these must be automatic, positive and under control.

In Operation

The cylinder is kept cool by water circulating through the water-jacket of the cylinder. The water is circulated by a pump attached to the shaft. The vapor is supplied by the carburetor or vaporizer, devices that properly mix the gasoline and air. The vapor is drawn into the cylinder by the piston, which in this connection acts as a pump. The charge is compressed by the return stroke of the piston, and when so compressed is fired by an electric spark. The explosion of the com. pressed charge imparts an impulse to the down stroke of the piston, a portion of the energy being stored in the momentum of the fly wheel. This stored energy completes the revolution and compresses the next charge. The pistons and connections are lubricated by sight feed and compression oil cups, using for the gas-engine cylinder oil.

Two And Four Cycle Motors

The gasoline motors in general use operate as stated, on the one principle. They vary only in the application of the same principle. There are two important variations. First, in the number of revolutions made to each impulse. Second, in the igniting device. With reference to the first, a motor that makes one complete revolution of the shaft to each impulse is called a two cycle. (The piston makes two motions - up and down.) A motor that makes two complete revolutions of the shaft to each impulse is called a four-cycle. (The piston makes four motions - up, down; up, down). There are arguments in favor of and against both types, which we will state and comment on.

The Two Cycle Motor

The two cycle motor having an impulse to each revolution will have twice as many impulses as a four cy-cle. This results in a more even distribution of the power, hence less vibration. To state this in another way - a four cycle, to develop the same power on the same number of revolutions, would require twice as strong an impulse, as it would have but half the number of them.

The two cycle has this objection - that the compressed charge is not as pure, and that a slight portion of it is wasted. Theoretically the.impulse given by the explosion takes effect when the piston is at the top of the cylinder, driving it down. Near the bottom of these is the exhaust outlet, and the other is the inlet for the new charge. As both of these are practically open at the same time, a slight amount of the new charge may pass through without being compressed, and as the new charge is taken in at the same time that the old one is exhausted, a part of the latter may not escape. Hence, theoretically the two cycle has not as pure a mixture as the four cycle. This objection is partly remedied by the deflector, which is a plate on top of the piston that deflects the new or entering charge up and away from the exhaust port.