How Does Power Or Self Start Work

Starter motor of a Royal Enfield motorcycle
Starter motor of Royal Enfield

Do you remember the time, when all the motorcycles used to be kick start? Or have you ever got an opportunity to ride a bike not having power start ? Kick start motorcycles were prevalent for a very long time. Starting these bikes in cold was a massive challenge. It required huge strength and stamina making It a troublesome experience for the old and weak people. To eliminate this problem and make the starting convenient, power starts were introduced. The starting became easier  and convenient thereafter. This made the Self start motorcycles very popular and kicks just remained as an emergency starting mechanism on bikes

Components Of Power Starting System

The main components of self start system are:
1. Self Switch
2. Staring Relay
3. Starter Motor
4. One Way Clutch

We will discuss about all these components in detail. But before reading about the components, we need to understand the process by which the engine start. So let's understand the engine cranking first. 

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Engine Cranking

For a very long period of time kick starts are being used as the starting mechanism
Motorcycle kick

Engines are generally shelf sufficient to carry on their operation once started. What we need to do is to bring all the components in motion at sufficient speed. For this either we can use kick or starter motor. You might also have seen electric generator engines being started by handles, even handles have the same function. When crank shaft is rotated, it reciprocates the piston from TDC to BDC. It also makes the intake and exhaust valves operational. The alternating current generator connected to the crankshaft also becomes operational and starts generating sparks inside engine at time of power strokes. The reciprocating piston sucks the air inside through carburator. The carburator mixes the air with fuel and this mixture is sucked inside the combustion chamber, which is burnt to produce power. In this way the operational cycle of engine is initiated. This cycle, once initiated can sustain itself. This whole process of making engine operational is called engine cranking.

Also read: Motorcycle frames

Self Switch And the Starter Relay

The starter motor needs the power supply from the battery to crank the engine. This power supply is governed by the self switch and the starter relay. The starter relay is a switch which connects or disconnects the power supply to the starter motor. The relay switch can be activated or deactivated by pressing or releasing the self switch. As soon as we press the self switch, the the relay connects the battery to the starter motor. This cause the motor to spin and crank the engine. The relay disconnects the supply as we release the self switch, disconnecting the motor from the battery. 

Working of starter motors

You might have seen starter motors mounted on the top of the engines and have wondered about their working. In this post we will look at the working of starter motors and engineering behind their use. Earlier , all the motorcycles used to have kick start but now most of them are having self start along with the kick. The basic mechanism behind the kick and starter motors is same. Both crank the engine by rotating the crankshaft starter motors are mounted on engines with their one terminal connected to the battery and self switch through starter relay. Their other terminal is connected to the frame which again is connected to the negative terminal of the battery. Their rotating shaft is connected to the crankshaft through starter gear which is connected to the crankshaft through one way clutch. When we press self switch the starter motor rotates. The rotating starter motor rotate the starter gears  which further rotates the crankshaft and starts the engine. When we disengage the self switch the starter motor stops rotating while the crank shaft keeps on rotating as the engine has been started. Now a question must have arisen to your mind that when the motor is connected to the crankshaft through gear arrangement than rotating crankshaft must now rotate the starter motor. But in reality this do not happen. Here the one way clutch arrangement comes in to play. The one way clutch works in such a way that it transfers the power from starter motor to the crankshaft but it can not transfer the power from the crankshaft to the starter motor. In other words starter motor can make the crankshaft rotate, but the crankshaft can not make the starter motor do so. Now lets see how does this one way clutch work

Working Of One Way Clutch

One way clutch used in starter motors

The one way clutches are based on  free wheel mechanism. They consist of inner and outer races and the spring loaded rollers are fixed in the cage between the two. When the inner  race is rotated clockwise, both the races get locked due to the roller and hence both of them rotate with each other. But when outer  race is rotated  clockwise the roller is not able to lock them both and hence the inner  race remains free. Again when the outer race is rotated anti-clockwise the rollers will lock both the races and they will rotate together. But the same will not happen  if the inner race is rotated anticlockwise. These one way clutches are fixed on fly wheels and their inner race is mounted on the hub of the starter gear in such a way that when starter gear  is rotated the inner and the outer races rotate together. But the same is not true when the starter motor stops and the outer race is rotated by flywheel. In that case the inner race remains free and do not rotate at all.


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