Fig. 116.—Forms of Pistons Commonly Employed in Gasoline Engines. A—Dome Head Piston and Three Packing Rings. B—Flat Top Form Almost Universally Used. C—Concave Piston Utilized in Knight Motors and Some Having Overhead Valves. D—Two-Cycle Engine Member with Deflector Plate Cast Integrally. E—Differential of Two-Diameter Piston Used in Some Engines Operating on Two-Cycle Principle.
A number of piston types are shown at [Fig. 116]. That at A has a round top and is provided with four split packing rings and two oil grooves. A piston of this type is generally employed in motors where the combustion chamber is large and where it is desired to obtain a higher degree of compression than would be possible with a flat top piston. This construction is also stronger because of the arched piston top. The most common form of piston is that shown at B, and it differs from that previously described only in that it has a flat top. The piston outlined in section at C is a type used on some of the sleeve-valve motors of the Knight pattern, and has a concave head instead of the convex form shown at A. The design shown at D in side and plan views is the conventional form employed in two-cycle engines. The deflector plate on the top of the cylinder is cast integral and is utilized to prevent the incoming fresh gases from flowing directly over the piston top and out of the exhaust port, which is usually opposite the inlet opening. On these types of two-cycle engines where a two-diameter cylinder is employed, the piston shown at E is used. This is known as a “differential piston,” and has an enlarged portion at its lower end which fits the pumping cylinder. The usual form of deflector plate is provided at the top of the piston and one may consider it as two pistons in one.
Fig. 117.—Typical Methods of Piston Pin Retention Generally Used in Engines of American Design. A—Single Set Screw and Lock Nut. B—Set Screw and Check Nut Fitting Groove in Wrist Pin. C, D—Two Locking Screws Passing Into Interior of Hollow Wrist Pin. E—Split Ring Holds Pin in Place. F—Use of Taper Expanding Plugs Outlined. G—Spring Pressed Plunger Type. H—Piston Pin Pinned to Connecting Rod. I—Wrist Pin Clamped in Connecting Rod Small End by Bolt.
Fig. 118.—Typical Piston and Connecting Rod Assembly.