Car kickstarter relay solenoid teardown - Inside the kickstarter solenoid

Car kickstarter relay solenoid teardown - Inside the kickstarter solenoid

This blog post is meant to satisfy the curiosity of people who may have wondered what is in the kickstarter solenoid. The solenoid is often a sealed unit such that once it develops a fault, it is simply replaced.

We cut one kickstarter solenoid open with a hand saw as shown in the image of this post. The part that is often problematic which is the high current relay contact is our area of interest.

Sometimes, when the solenoid fails, we hear only a click sound when we attempt to start the car. This is because the relay contact has failed.

Why is this relay necessary?

This relay is there because the kickstarter is meant to work only during engine cranking period. The kickstarter is fed electrical energy and this energy is then converted to mechanical energy (rotational motion) by the electric motor. The kickstarter turns with a torque (rotational force) that is sufficient to turn the engine and make it to start.

When the engine has started and the key is returned from the "start position", the kickstarter is de-energised and is in a rest state.

The relay feeds power to the armature through the carbon brushes and slip rings. The power is directly tapped from the battery and it is "hot" (power is always there), hence the need for a relay. If this relay is not there, the kickstarter will continue to turn even after the engine has started.

 How does this part fail?

  1. The internal contacts can burn out causing a very high resistance to current flow or no contact at all.
  2. The plate shown in the lower left part of the picture which makes contact with the input and output terminals can bend causing lack of contact. This happens especially when there are multiple start attempts and it has heated up, hitting the contacts now makes it easier to bed.
  3. On the terminals inside the solenoid, there is a softer coating (which looks like a carbon coating). This is there to prevent iron to iron contact that will cause large spark, heat and melting together of the terminals with the plate that short-circuit both terminals. This coating can either detach from the terminal or also burn-out.
  4. Another way that there can be failure is when the solenoid itself is not working. In this state, the contact plate cannot move to bridge the two terminals.
  5. Another simple cause of no-start is when there is loose connection at any of the terminals.

In a state of emergency, a quick way to start the car is to get a wire that can conduct the kickstarter current and bridge the two terminals while starting the car. This wire should be removed immediately the engine starts.

Another temporary solution is getting a contactor (a high current relay) and connect it to act in place of the kickstarter relay until the car is safely taken to a mechanic workshop for proper repair.