If you look at the 4 strokes of a IC engine, in every stroke, some resistance will be present. At the third stroke that is in the compression stroke, the resistance will be more as it is compressing the fuel air mixture present in the combustion chamber. Due to the process of compression, high pressure is built which is necessary for the combustion to happen. If you see a catalogue of any motorbike, you can able to see a compression ratio of the engine used in that motorbike which somewhere lies between 8:1 to 14:1. Simply saying, compression ratio refers to the ratio of maximum to minimum volume in the cylinder.
Still now, some classic motorbikes with mid range capacity comes with a kick start mechanism. If we try to start the motorbike using kicker, the pressure is already built and present in the combustion chamber due previous cycle of running. If we use the kicker, extra fuel air mixture enters the combustion chamber which results in more compression and pressure buildup than needed. If the compression is more than normal, the piston returns to the Bottom Dead Center (BDC) vigorously due to the presence of more pressure and forces the kicker to act backwards which might end up in hurting our leg. So, at the initial stage of starting the motorbike, there'll be a need of releasing some pressure. For this purpose, manual decompressor is designed and utilized in motorbikes.
During kick starting, low compression inside the combustion chamber allows us to kick it easily. If not, high compression of the engine results in reverse action of the kicker and cause problems as we know. Generally in the head assembly, a inlet valve for letting the fresh fuel air mixture inside the combustion chamber, a exhaust valve for letting the burnt fuel air mixture outside the combustion chamber and a sparkplug for igniting the compressed charge will be present. In addition to that, a decompressor will also be added in the head. This decompressor is connected with the cable which is routed and connected to the lever present in the handlebar. In some motorbikes, this lever is present near the engine head itself.
Simply saying, the decompressor module simply acts like a small plunger which is bolted to the engine head. When rider pushes the decompressor lever present in the handlebar, the small piston arrangement present inside the decompressor module comes out. As we know combustion chamber is fully sealed during compression and in expansion stroke, this piston present in the decompressor module allows some of the pressure to leak through it and leading it to the exhaust manifold. Due to the reduction in pressure, now we can able to easily kick start the motorbike.
Surely, a doubt will be bloomed in your mind that why the decompressor lever is pushed where others like clutch, choke cables are activated with the help of pulling it. If we fail to pull back the decompressor lever, there are chances for mechanical damages and the engine runs with low compression which results in poor performance and mileage. So, the pushing mechanism is used here. As i said, cable attached to the lever pushes the piston from the decompressor unit. Cable's body near the decompressor unit is loaded by spring. After pushing the lever and after the bike has been started, once you take your hand off the lever, it'll come back to its original position thereby closing the passage to avoid the above mentioned problems.
Still now, some classic motorbikes with mid range capacity comes with a kick start mechanism. If we try to start the motorbike using kicker, the pressure is already built and present in the combustion chamber due previous cycle of running. If we use the kicker, extra fuel air mixture enters the combustion chamber which results in more compression and pressure buildup than needed. If the compression is more than normal, the piston returns to the Bottom Dead Center (BDC) vigorously due to the presence of more pressure and forces the kicker to act backwards which might end up in hurting our leg. So, at the initial stage of starting the motorbike, there'll be a need of releasing some pressure. For this purpose, manual decompressor is designed and utilized in motorbikes.
During kick starting, low compression inside the combustion chamber allows us to kick it easily. If not, high compression of the engine results in reverse action of the kicker and cause problems as we know. Generally in the head assembly, a inlet valve for letting the fresh fuel air mixture inside the combustion chamber, a exhaust valve for letting the burnt fuel air mixture outside the combustion chamber and a sparkplug for igniting the compressed charge will be present. In addition to that, a decompressor will also be added in the head. This decompressor is connected with the cable which is routed and connected to the lever present in the handlebar. In some motorbikes, this lever is present near the engine head itself.
Simply saying, the decompressor module simply acts like a small plunger which is bolted to the engine head. When rider pushes the decompressor lever present in the handlebar, the small piston arrangement present inside the decompressor module comes out. As we know combustion chamber is fully sealed during compression and in expansion stroke, this piston present in the decompressor module allows some of the pressure to leak through it and leading it to the exhaust manifold. Due to the reduction in pressure, now we can able to easily kick start the motorbike.
Surely, a doubt will be bloomed in your mind that why the decompressor lever is pushed where others like clutch, choke cables are activated with the help of pulling it. If we fail to pull back the decompressor lever, there are chances for mechanical damages and the engine runs with low compression which results in poor performance and mileage. So, the pushing mechanism is used here. As i said, cable attached to the lever pushes the piston from the decompressor unit. Cable's body near the decompressor unit is loaded by spring. After pushing the lever and after the bike has been started, once you take your hand off the lever, it'll come back to its original position thereby closing the passage to avoid the above mentioned problems.
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