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Saybolt viscosimeter. The standard merican instrument used to measure the viscosity of oils.
Scavenging. The removing from the engine cylinder, by a stream of slightly compressed air, of the products of combustion of the preceding cycle.
Screen. A wire cloth with a fine mesh used to remove dirt from oil or water.
Seal. Any device to prevent leakage of gas or liquid, oil or water.
Semidiesel engine. A term applied to oil engines using rather low compression pressures and requiring a hot surface for ignition of the injected fuel.
Sensitivity. Change in engine speed before the governor begins to act.
Servomotor. A motor operated by oil or air pressure and used for operating heavy control mechanisms.
Shaft. A round bar of steel or other strong metal that is used to transmit rotary action.
Shaft horsepower. The power rating of a diesel engine used for turning a propeller shaft in marine installations. Abbreviated shp.
Shell. The steel or bronze backing to which the babbitt of a shaft bearing is bonded. Also the whole removable bearing.
Shim. A thin sheet of metal or other material which is inserted between two machine parts to obtain their correct relative location.
Silencer. A device to deaden the sound of the intake or exhaust of an engine; a muffler.
Silent chain. A chain made up of small pins and steel plates that engage the teeth on sprockets resembling spur gears, and that is used to transmit power from one shaft to another and by its construction is less noisy than the ordinary roller chain.
Skirt. The lower part of the piston. Also the lower part of a liner if it protrudes below the cylinder jacket.
Sludge. A tar-like formation in oil resulting from the oxidation of a portion of the oil.
Solid injection. A rather misleading term applied to airless injection.
Specific fuel consumption. The fuel consumption per hour pided by the brake, or shaft, horsepower developed, expressed in lb. per blip or lb. per shp.
Specific gravity. (1) Weight of a liquid or solid compared with the weight of an equal volume of water at 60 F. (2) For a gas, its weight as compared with the weight of an equal volume of air at the same temperature and pressure.
Specific heat. The amount of heat needed to raise the temperature of one pound of the substance one degree Fahrenheit.
Speed droop. The difference in speed between no-load and full-load engine speed.
Spray valve. The fuel injector.
Spring. A coiled piece of round or square steel wire which, when compressed, exerts a force that may be used to do some work.
Stability. (1) Ability of lubricating oil to withstand physical change under severe operating conditions. (2) Ability of a governor to maintain the required engine speed without fluctuations or hunting.
Stress. The internal forces set up in a body when it is subjected to forces tending to deform it by tension, compression, shear, bending, or torsion.
Stroke. The distance a piston travels up or down inside the cylinder.
Suction stroke. The stroke of the piston of a four-stroke engine during which a fresh charge is sucked in or forced by atmospheric pressure into the space vacated by the piston.
Supercharging. Supplying of combustion air to an engine at higher than atmospheric pressure, usually 2 to 4 psig, in some engines up to 30 psig.
Surface-ignition engine. The semidiesel engine.
Synchronous. Occurring at the same time or in phase.

Internal-combustion engine glossary

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