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Two stroke and four stroke engine structure differences and maintenance features Engine maintenance
252 Hits  Issue date:2/24/2013

Engine maintenance characteristics

As a result of the two stroke engine and four stroke engine structure in the presence of these differences, so 2 kinds of engine fault diagnosis and maintenance characteristics are also different. Now with less engine power, poor acceleration fault as an example to be described.

Engine power shortage, poor acceleration fault, affecting a wide range, almost relates to the engine systems. In order to state conveniently, leaving the motorcycle ignition system, a transmission system and a cylinder piston and other factors are excluded. Two stroke and four stroke engine of the fault was mainly due to the gas distribution mechanism, the combustible mixed gas seal, its diagnosis, maintenance of the basic train of thought to also have a characteristic each.

1, four stroke engine troubleshooting features

A ) gas distribution mechanism

Four stroke engine valve mechanism is mounted with more stringent requirements, as long as the flywheel of a magnetic motor assembly when the timing mark line on crankcase ( or the box cover ) the timing mark hole groove, in this position under installing camshafts, timing sprockets and timing chain. If the engine is disassembled after the valve timing after the power shortage, poor acceleration fault, if carefully proofread and reinstall the valve timing can rule out the possibility of failure. If the motorcycle is running tens of thousands of kilometers after such a fault, and often need to adjust the valve clearance, accompanied by abnormal sound of engine cylinder head, difficult to start trouble, should be suspected in camshaft appeared abnormal wear or distribution mechanism and its related parts appear flat, must make a thorough examination: 1) camshaft wear: the engine running a long period of time, because of lubrication, cooling system abnormity or parts of the quality problem, and by some other uncertain factors, the camshaft lift parts wear, over the use of the limit value, the gas distribution phase open angle will be correspondingly shortened, so that the gas distribution phase change cam shaft; or two journal and bushing bore wear serious, so that the cam shaft generated in the rotation process of the radial displacement, resulting in valve opening is reduced, air valve starting deficiency. These 2 kind of situations will cause the engine speed characteristic to the low speed moving motorcycle, power and acceleration of natural variation. At the same time, along with the gas distribution mechanism of running noise increases gradually. 2) valve leakage: If due to multiple factors, appear valve ablation, valve rod, valve spring bending elastic weakening, etc, into the exhaust valve is sealed and lax, formation of leakage. The reasons are: the valve and valve seat due to carbon rather than bad sealing, the valve and valve seat sealing surface matched with the eccentric wear generated, valve clearance is too small or no gapless, so that the valve mechanism to open early and late closure, engine temperature, heating parts expansion natural extended automatically top to open the valve, so that the valve is not tightly closed, causing gas leakage. The valve is not tightly closed, there may be the valve spring resulted in decreased, therefore, in the removal of valve leakage process, do not neglect to check valve spring.

B ) cylinder head gasket leaks air : not according to stipulation torque fastening the cylinder head bolts or nuts, or driving after tens of thousands of kilometers of cylinder head bolt and nut for various reasons resulting in loose; upper surface of cylinder or cylinder head plane processing reach technical requirements, the flatness of serious out of tolerance; the cylinder body and a cylinder cover plane in the operation of the engine after deformation and warping; both sides of cylinder pad coated fluorine rubber ( some gasket coated nitrile rubber ) off; cylinder head gasket leaks air, can make the combustible mixed gas, the loss of engine power.

C ) inlet pipe leaking into the trachea: if the rubber part due to deterioration of cracking, or intake manifold and cylinder cover between the O ring aging, or at the intake tube is not tighten to the specified torque, can cause air leakage phenomenon, when the engine is working into the air, causing the combustible mixed gas, power drop.

2, two stroke engine troubleshooting features

A ) two stroke engine valve mechanism is arranged in the cylinder body or the crankcase, the valve position cannot be changed. If the mixed gas in the oil content is overmuch, burning after the formation of the deposition in the airway opening cylinder, interferes with the normal engine scavenging and exhaust, make the engine exhaust is not suitable, resistance increase. Therefore, for tens of thousands of kilometers travel car, should focus on the examination of cylinder port is blocked? In addition, if the exhaust muffler of carbon deposition of excessive, will also increase the exhaust gas in the exhaust resistance, resulting in the loss of engine power.

B ) two stroke engine determines the structural characteristics of the crankcase parts of the seal (including air inlet pipe, a carburetor ) there can be no leakage. If the crankcase sealing resulting in leakage, can cause the engine to reduce the combustible mixed gas suction, thinning, power loss. The focus of the inspection are: left, right crankcase combination of surface leakage (mainly flatness oversize or sealant liquid failure ), or crankshaft oil seal is serious ageing, oil seal lip and crank shaft neck sealing leakage, or reed valve and valve seat of warping is excessive, and spring seat the rubber layer is not resistant to gasoline and layer off, so that the sealing failure. In addition, the crankcase sealing bad, will cause cold hard starting failure.

C ) two stroke engine and four stroke engine matching carburetor type is different, and the difference of the carburetor idle speed oil. In the adjustment of two stroke carburetor air adjust screw, counterclockwise direction rotary air adjust screw, is to increase the amount of air entering the idle speed oil system, combustible gas mixture will be thin; clockwise into rotary air adjust screw, is to reduce the volume of air entering the idling oil system, combustible mixture thicken. If the amount of air into the carburetor too much ( especially during the cold winter months ), will directly affect the engine acceleration performance. Therefore, during the regulation should be based on the climate changes in flexibility, half in the winter to offset a little thick, i.e. by vehicle manual rules will air adjust screw clockwise to spin a little; summer is offset to dilute some (upcoming air adjust screw counterclockwise direction to the swing a point. Its adjustment, in order to slow throttle engine as standard.

To sum up, in four stroke engine and two stroke engine working principle, structure, its maintenance methods and characteristics are also different. For the four stroke engine, should periodically check the machine oil pump screen is blocking, to ensure the smooth lubrication, adhere to the replacement of lubricating oil. Tens of thousands of kilometers for running vehicle, if the engine acceleration variation, and the inlet, exhaust valve clearance adjustment of the operation often needs, noise also increases with each passing day, should be timely check camshaft lubricating and wear, as well as the cylinder liner and the presence of aging at the intake tube cracking and other anomalies, and on-condition replacement of damaged parts. For the two stroke engine, it must ensure that the pump can work normally, the oil flow is moderate, depending on the specific circumstances of temperature, adjust the carburetor mixture proportion; focus on examination of the existence of bad sealing the crankcase, and periodic removal of spark plug, the combustion chamber, gas cylinder scavenging port and the exhaust port and the exhaust muffler of carbon deposition, to ensure the smooth sweep gas, exhaust gas clean.

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