Tractor Engine Parts
Principal Engine Parts
1. Base or Frame
3. Cylinder Head
5. Piston rings
6. Piston Pin
7. Connecting rods
10. Valve System
11. Fuel Supply and carburetion system
12. Ignition system
13. Cooling System
14. Lubrication System
15. Governing System
Base or Frame
The base or frame of an engine is that part, usually made of cast iron, to which other parts of the engine are directly or indirectly attached. It is equipped with holes, usually four in number, by which the engine may be firmly anchored to its foundation.
Cylinders are made of high-grade gray cast iron and may be cast with the engine base or cast separately. The former construction is confined largely to the smaller sizes of engines, whereas the detachable cylinder is preferred in the medium and larger sizes. Attaching the cylinder and base together produces rigid construction but necessitates a greater outlay if the cylinder must be replaced when worn or damaged. If the cylinder is not a part of the base but bolted to it, care should be taken to keep the bolts tight and retain the proper cylinder alignment at all times, thus reducing breakage and wear.
Cylinder heads are made of cast iron. In most cases, they are detachable from the cylinder but sometimes cast with it. When casted separately, a gasket of some nonburning material must be used to prevent loss of compression and leakage of the cooling liquid. The detachable type of cylinder allows better accessibility and it is more convenient to get to the valves and clean the carbon from the cylinder piston.
They are ordinarily made of cast iron, but aluminum-alloy pistons are frequently used in multiple cylinder engines. Aluminum alloy offers the advantage of being lighter in weight but has greater coefficient of expansion and must be given more clearance than the cast-iron piston of the same size.
Piston of an engine is made to move back and forth in the cylinder owing to the explosion of the fuel mixture. This back and forth movement of the piston is transmitted through the connecting rod and crankshaft to the belt pulley and thus power is generated. Piston clearance is the space between piston wall and cylinder wall. For cast iron pistons, clearance is about 0.001 in. of the cylinder diameter.
Aluminum alloy pistons require about twice as much as clearance as cast-iron pistons. Too much piston clearance will cause loss of compression, oil pumping and piston slap. Too little clearance will cause the piston to stick or seize in the cylinder as the engine gets hot. A piston may seize in a cylinder even though it has the proper clearance, owing to the improper action of the cooling system or to lack of cylinder lubrication.
Piston rings are made of cast iron. The number of rings per piston varies from three to seven depending upon the type of engine and the compression desired. The ordinary type of engines seldom have more than three or four rings, although five may be used in tractors and in heavy duty engines.
The function of the piston rings is to retain compression and reduce the cylinder-wall and piston wall contact area to a minimum, thus preventing friction losses and excessive wear. Piston rings are classified as compression rings and oil rings depending upon their specific function and location on the piston.
Compression rings are plain one-piece rings and are always placed in the grooves nearest the piston head. Oil rings are grooved slotted and are located either in the lowest groove above the piston pin or in a groove near the piston skirt. It controls the distribution of the lubricating oil to the cylinder and piston surfaces and to prevent unnecessary or excessive oil consumption.
Piston pins are made of case hardened steel. The function of the piston pin is to contact the connecting rod to the piston and provide a flexible or hingelike connection between the two.
3 methods are used to anchor piston pins that they cannot work sideways and score the cylinder. The first is to clamp the pin to the connecting rod by means of a clamp screw or setscrew, so that the bearing will be at each end of the pin where it fits in the piston by means of set screws and the bearing is in the connecting rod. In the third method, the piston pin is allowed to float, so to speak, or move in both the piston and connecting rod, but is held in place by means of retaining rings at each end of the pin.
Connecting rod are made of what is known as drop-forged steel. They must be of some material that is neither brittle nor ductile. The I-beam type is the prevailing connecting-rod shape. It gives strength with less weight and material. Another type of connecting rod known as a marine-type connecting rod is so made that both halves of the bearing are removable from the connecting rod proper. That end of the rod fastened to the piston pin is known as the small end and the other end, which is attached to the crankshaft, is spoken of as the large end of the connecting rod. The large end ordinarily has what is known as a split bearing. The bearing metal, usually babbitt, may be cast directly in the connecting rod or in a removable bronze or steel backing or shell.
Crankshafts are made of drop-forged steel and carefully machined, ground and polished at the bearing points or journals. The journals that support the crankshaft and hold it in position are called main journals, whereas the part to which the connecting rod is attached is spoken of as a crank journal.
Flywheels are made of cast iron and serve two purposes. They assist in maintaining a uniform engine speed, especially in one-cylinder engines, and provide a means of balancing the engine properly so that vibration and wear are reduced to a minimum. Uniformity of speed is maintained by the inertia of the heavy flywheel.