MAJOR PARTS OF AN IC ENGINE
ENGINE COMPONENTS
1. CYLINDER BLOCK
The cylinder block is the main body of the engine. Cylinder head is mounted on the cylinder block. It houses iniet and exhaus valves. Crank case is attached to the bottom of the cylinder block. Crank case supports the crank shaft. Oil pan is attached to the bottom of the crank case.
Cylinder block contains large cylindrical holes called cylinder bore. The cylinders are accurately finished to accommodate pistons. The space above the piston inside the cylinder at TDC called the combustion chamber. Combustion of fuel inside this space, high pressure and temperature will be developed inside the cylinder. Therefore, it should be made of material which can resist high pressure and temperature
(2800°C). In water jackets has around the cylinders for the circulation cooling water to absorb the temperature while running of an engine.
2. CYLINDER HEAD
Cylinder head is a separate casting placed on top of the cylinder block by studs and nuts. It houses the inlet and exhaust valves, spark plug hole (SI engine) or fuel injector hole and cooling water jacket.
A gasket is placed between the cylinder block and cylinder head to prevent leakages caused by compression. A copper asbestos, sometimes steel asbestos gasket is used. On the top of cylinder head, rocker arm assembly unit is placed for operating overhead Inlet and outlet valves.
3.CRANK CASE
It may be cast integral with the cylinder block. Some times it cast separately and bolted to the cylinder block. It supports the crank shaft and cam shaft with the help of bearings. It imparts safety also from the probable accidents on account of moving parts. Gaskets are used to seal the joint between cylinder block and crank case. Some times, the bottom of crank case may be used as oil pan, which stores the lubricating oil for engine lubrication.
4. OIL SUMP/PAN
Oil pan is fitted at the bottom of crank case by using gaskets. It serves as a reservoir and allows the oil for lubricating the engine. Its capacity depends upon the size of the engine. A drain plug is provided to the oil pan to drain out the oil.
5. CYLINDER LINER
The cylinder liners are cylindrical components that fit inside the cylinder bore. Inside the cylinder, the piston reciprocates up and down which causes wear and tear of cylinder. When the cylinder diameter is increased beyond certain limit, we have to replace the entire cylinder block which is a costly affair. Hence a separate liner can be inserted in the cylinder bore to reduce this wear.
Whenever the liners worn out, they can be replaced easily. Whenever a cylinder block is re - bored beyond allowable limits, liners are used to restore it's original size.
a) DRY LINER
These liners have metal to metal contact with the cylind block. They are not directly in touch with cooling water in water jack and hence it is called as dry liners. Dry liners are made in the form barrel. It is fitted inside the cylinder block with interference fit. A flange is provided at the top which keeps the liner into position in the cylind block.
If the liner is too tight, it produces distortion of cylinder block liner cracking, hotspots and scuffing. If the liner is too loose in th cylinder block, it results in poor heat dissipation because of absence of good contact between the cylinder and the liners. This will result higher operating temperature and also results in piston scuffing.
B) WET LINER
These liners are surrounded by cooling water and hence it called as wet liners. At the top, the liner is provided with a flange which fits into the groove in the cylinder block. At the bottom, either the cylinder block or liner is provided with three grooves. The middle groove is left empty and top and bottom are inserted with packing rings made of synthetic rubber. For water leakage, drainage arrangements are provided from the middle groove.
Wet liners are provided with a coating on outer to resist corrosion. In general, wet liners are also thicker than dry liners. Their thickness range from 1.5 to 3.0 mm. A worn out liner can be removed and replaced with a new one easily.
6. PISTON
It is a main active part of the engine. It is a cylindrical shaped mass that reciprocates inside the cylinder. Pistons are long hollow objects, open at the bottom and closed at the top. The top portion of the piston is called as the “Crown". At the piston top, three grooves are cut to accommodate the piston rings and the bands left between the grooves are known as lands. They support the rings against gas pressure.
7. PISTON PIN
The piston pin is used to connect the piston and the connecting rod small end. The another name of the piston pin is wrist pin or gudgeon pin. It transfers combustion chamber pressure and piston forces to the connecting rod.
8. PISTON RINGS
Piston rings are located towards the top of the piston. Piston rings are inserted into the three grooves on the peripheries of the piston to maintain a good seal between the piston and cylinder walls. The top two piston rings are called compression rings and are designed to maintain cylinder pressure. The bottom ring is called oil ring. The rings are slightly larger in diameter than the piston.
A) COMPRESSION RINGS
It is used to prevent any leakage of the gases and form a seal between the piston and the cylinder walls. Each piston is provided with two compression rings, one at the bottom and another at the top. Rings are manufactured with butt joint, angle joint, lap joint etc. Its cross section is rectangular. Heavy duty engines have three or more rings.
B) OIL RINGS
As the piston moves up and down, it rubs against the inner cylinder wall. This causes
scratches on the piston and cylinder wall surfaces. In order to prevent this rubbing action, oil is splashed from oil pan on to the cylinder wall when the piston moves up.
When the piston moves down, the oil rings scrape the oil from the cylinder wall. Thus the oil is drained into the oil pan. Oil rings are used to provide an effective seal to prevent leakage of lubricating oil into the cylinder. It is inserted into the middle groove of the piston. Oil vent (slot) passages are provided in the oil rings, all around at certain spacing in the channel. After scrapping the lubricating oil from the cylinder interior, they allow oil to flow back through the oil vents (slot).
10. CONNECTING ROD
Connecting rod is the intermediate link or connecting element between the crank shaft and the piston. The expanding gas force on the piston is thus transmitted to the crank pin through this rod. It has two ends namely small end and bigger end. The small end is connected to the piston through gudgeon pin. The big end of the connecting rod is fastened to the crank pin in the crank shaft through the cap, rod bolts and nuts. The Connecting rod usually has circular, rectangular, T or H, I-beam cross section.
11. CRANK SHAFT
It is used to convert reciprocating motion of the piston into rotary motion. Big end of the connecting rod is connected to crankshaft. On rear end of the crank shaft a flywheel is mounted which acts as an energy reservoir. On the front end of the crank shaft, a timing gear or sprocket, a vibration damper and a pulley for driving the water pump, fan and generator (dynamo) are mounted. The main parts of the crank shaft are main journals, crank pins, crank webs and counter weights.
Crank shaft is supported on the main bearings, which are fitted in the lower portion of the crank case.
12. CAM SHAFT
It is a type of shaft which contains cams to change rotary motion into straight line or linear motion. It operates the inlet and exhaust valves through rocker arms. Cam shaft is driven by the crank shaft through a chain and sprocket. The cam shaft rotates at half of the engine speed ie., power is supplied to the cam shaft in 2 : 1 ratio.
13. FLY WHEEL
Flywheel is a reservoir of energy mounted on the rear end of the crankshaft. To store up energy during power stroke and release it during other strokes. The size of the fly wheel varies as per the number of cylinders in the engine. It is a heavy Grey cast iron body attached to the flange of the crank shaft with nuts and bolts.
MATERIALS & FUNCTION OF ENGINE COMPONENTS
