2．Tappet, Pushrods and Rocker Arms
Tappet rests on a cam of the camshaft. The pushrod is a metal rod that fits between the tappet and the rocker arm. Its function is to transmit cam lobe lift to the rocker arm assembly. The rocker arm is nothing more than a lever. Its function is to convert the up wardmotion of a pushrod into downward motion that compresses the spring and opens the valve.
练一练
气缸体
气缸盖罩
油底壳
气缸盖 气缸垫
1- cylinder head cover;
2-cylinder head;
3- cylinder gasket; 4-cylinder block; 5- oil pan
Components of piston
piston top
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（1） The Connecting Rod
The connecting rod links the piston to the crankshaft. The small end of connecting rod connects with the piston pin and the big end connects with the crank pin of the crankshaft.
3．Valves and Valve Springs
Modern engines have cylinder heads that contain valves. Each cylinder requires at least two valves：an intake valve and an exhaust valve. The valves are compressed and closed by valve springs. As the valve is opened by the camshaft, it compresses the valve spring.
oil rings piston pin piston connecting rod
crank bearing half shell曲 柄轴承半壳 connecting rod cap
2．Crankshaft Flywheel Group （1） Crankshaft The crankshaft is the main rotating shaft of the engine. Designed into the one-piece crankshaft are areas for main bearing journals, crankpins, counterweights, flywheel flange, and driving hub. The crankshaft and connecting rod convert the reciprocating motion of the piston to the rotary motion of crankshaft. Crankshafts have drilled oil passages, through which oil can flow from the main bearings to the connecting-rod bearings.
陈长梅
One. Crank-Connecting Rod Mechanism
Crank-connecting rod mechanism consists of pistonconnecting rod group, crankshaft flywheel group, engine block group.
valve
push rod
■ Valve gear阀装置 Tappet 挺杆 ■ Connecting rod
timing gears
connecting rod
piston crankshaft
flywheel
Engine Body
cylinder head
cylinder block
The cylinder gasket 气缸垫
The piston
Piston top piston ring piston pin
connecting rod
Two. The Valve Train
The valve train is a series of parts used to open and close the intake and exhaust valves. Meshing the timing gears or installing the timing chains onto the sprockets at a specific place will ensure the valves to open and close at the proper moment in the engine’s cycle. It consists of camshaft, tappet, pushrod, rocker arm, valve spring, valve and so on （Fig.2-4）.
Single-cylinder engine
Inlet valve Exhaust valve
Timing gear Oil pump
cylinder piston Piston pin Connecting rod
crankshaft Oil pipe
inlet valve exhaust
进水阀
piston head piston skirt
Small end小端 Connecting rod bushing连杆衬套 Connecting rod Big end
Connecting rod half shells半壳 Connecting rod cap
III. Exercises
compression rings
（2） The Piston The engine manufacturer fits a piston into each cylinder of the engine. The piston receives the pressure from the burning airfuel mixture and converts this pressure into up-and-down reciprocating motion. Because aluminum is half weight less than iron, most of pistons are made from aluminum alloy. （3） Piston Rings The piston ring is a springy split metal ring. It is used to provide the necessary seal to eliminate blowby and to control oil consumption. Engine pistons have two kinds of rings：gas rings and oil rings.
（2） Flywheel
The flywheel is a comparatively heavy wheel, bolted to the flywheel flange on the rear end of the crankshaft.
The inertia of the flywheel tends to keep it rotating at a constant speed. The flywheel also has several other functions, for example, the flywheel has ring gear in its outer circumference,which mesh with teeth located on the starting motor drive pinion in order to crank the engine over. In addition, the rear surface of the flywheel serves as the driving member of the clutch assembly （Fig.2-2）.
1．The Engine Block Group
（1） The Cylinder Block
The cylinder block is the basic part of the engine. It forms the main framework or foundation of the engine. Many parts of the engine are fixed to it. These items include water pump, oil pan, flywheel or clutch housing, ignition distributor, oil pump, fuel pump, and cylinder head.
1．Camshaft
The camshaft is another rotating shaft within the engine, it’s driven by the engine’s crankshaft through the timing gears. The camshaft has a series of cams that can change rotary motion to straight-line motion which cause the intake valves and exhaust valves to open. It rotates at the half speed of the crankshaft.