21-12-2012, 02:05 PM
TWO-STROKE ENGINE TOP-END DISASSEMBLY
Introduction
The Components of a Two-Stroke Engine Top-End Assembly shows an exploded viewofthetop-endassemblyofaliquid-cooledtwo-strokeengine.Thetop-endassemblyconsistsof the following parts:
• Cylinder head securing fasteners
• Cylinder base gasket
• Cylinder head washers
• Cylinder studs
• Cylinder head
• Cylinder
• Cylinder head gasket
• Piston
• Power valve assembly
• Piston rings
• Piston wrist pin
Working
Upward stroke: The piston is at the bottom of the cylinder. A pipe at the left side is opened and lets the fuel mixture, which is already compressed a bit, flow from the lower to the upper part of the cylinder. The fresh gases expulse now the exhaust through an ejection pipe, which is not closed by the piston at this moment.
2-stroke engine
Downward stroke: After being hurried upward, the piston now covers the pipe on the left side and the ejection pipe. Because there is no way out any more, the upper, fresh gas mixture gets compressed now. At the same time in the part below fresh gas is taken in by the piston driving upward through the open suction pipe. At the upper dead-center, the compressed fuel mixture is ignited by the sparking plug, the piston is pressed downward while he compresses at the same time the fresh gas below. The process begins again as soon as the piston arrives at its lowest point.
Two- cycle motors provide one power impulse for every revolution from the crankshaft.
The terms "two- cycle" and "two- stroke" are usually inter- changed while speaking about 2- cycle engines. These engines derive their name from the quantity of directional shifts that the pistons make through each power stroke. Internal combustion engines can be used to produce mechanical power from the chemical energy contained in hydrocarbon fuels. The power- making part of the motor's operating cycle starts in the motor's cylinders using a compression process. Two-cycle motors deliver one power impulse for each revolution of the crankshaft.
Following this compression, the burning of the fuel- air mixture then releases the fuel's chemical energy and produces high- temperature, high- pressure combustion materials. These gases then expand within each cylinder and transfer work to the piston. Thus, as the engine is operated continuously, mechanical power is produced. Each upward or downward movement of the piston is called a stroke.
Components
Connecting rod:
In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts linear motion into rotating motion. It consist of cast iron. As a connecting rod is rigid, it may transmit either a push or a pull and so the rod may rotate the crank through both halves of a revolution, i.e. piston pushing and piston pulling. Earlier mechanisms, such as chains, could only pull. In a few two-stroke engines, the connecting rod is only required to push.
Crank shaft: it consist of forged steel. Crankshaft is use to convrt the reciprocating motion in to rotary motion of the piston. It is connected with connecting rod at the crank pin. And by the main journal bearring it is rotating. At the end of the crankshaft the flywheel is mounted.
Cylinder head
Cylinder head: In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket. In most engines, the head also provides space for the passages that feed air and fuel to the cylinder, and that allow the exhaust to escape. The head can also be a place to mount the, spark plugs, and fuel injectors in case of C.I engine.
Cylinder block:
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures. In the case of two-stroke engines colling of the cylinder walls is done by the means of the cooling fince. Figure shows the fince it increases the contact area and so absorb more amount of heat frome the combustion chamber.
Assembling of Two – stroke Engine
1) Before you disassemble your engine, power-wash the engine and the rest of the vehicle. That will reduce the risk of dirt and debris falling into the engine. Once you remove the cylinder, stuff a clean rag down into the crankcases.
2) The cylinder and head use alignment pins to hold them straight in position from the crankcases on up. The pins make it difficult to remove the cylinder from the cases and the head from the cylinder. Sometimes the steel alignment pins corrode into the aluminum engine components. Try spraying penetrating-oil down the mounting studs before attempting to remove the cylinder and head. Never use a flat-blade screwdriver, chisel, or metal hammer to remove the cylinder. Instead use this technique; buy a lead-shot plastic mallet, swing it at a 45-degree angle upwards against the sides of the cylinder. Alternate from left to right, hitting the sides of the cylinder to separate it from the cases evenly. Clean the steel alignment pins with steel wool and penetrating-oil. Examine the pins closely. If they are deformed in shape, they won’t allow the engine parts to bolt together tightly. This can cause a dangerous air leak or a coolant leak. The pins are cheap at about $2 each. Replace them if they are rusty or deformed.
3) Never re-use old gaskets. Remove them with a razor blade or gasket scraper. Don’t use a drill-driven steel wool type pad to remove old gaskets because they can remove aluminum from the cylinder and head. That will cause a gasket to leak.