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Exhaust Manifold The exhaust manifold is a tube that carries waste products of combustion from the cylinders. On L-head engines the exhaust manifold is bolted to the side of the engine block on; overhead-valve engines it is bolted to the side of the engine cylinder head. Exhaust manifolds may be single iron castings or may be cast in sections. They have a smooth interior surface with no abrupt change in size (see fig. 12-1 1). Intake Manifold The intake manifold on a gasoline engine carries the fuel-air mixture from the carburetor and distributes it as evenly as possible to the cylinders. On a diesel engine, the manifold carries only air to the cylinders. The intake manifold is attached to the block on L-head engines and to the side of the cylinder head on overhead-valve engines. (See fig. 12-11.) In gasoline engines, smooth and efficient engine performance depends largely on whether the fuel-air mixtures that enter each cylinder are uniform in strength, quality, and degree of vaporization. The inside walls of the manifold must be smooth to offer little obstruction to the flow of the fuel-air mixture. The manifold is designed to prevent the collecting of fuel at the bends in the manifold. The intake manifold should be as short and straight as possible to reduce the chances of condensation between the carburetor and cylinders. Some intake manifolds are designed so that hot exhaust gases heat their surfaces to help vaporize the fuel. Gaskets The principal stationary parts of an engine have just been explained. The gaskets (fig. 12- 12) that serve as seals between these parts require as much attention during engine assembly as any other part. It is impractical to machine all surfaces so that they fit together to form a perfect seal. The gaskets make a joint that is air, water, or oil tight. Therefore, when properly
Figure 12-12.-Engine overhaul gasket kit. installed, they prevent loss of compression, coolant, or lubricant.
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