What Does a Solenoid Do On A Motorcycle? (Explained)

Motorcycles are in a vehicle class of their own—any two-wheelin’ enthusiast will tell you. 

Motorized bikes have been around for over a century by now, maybe almost a century and a half; most hard-hitting bike brands innovate their own technologies at this point.

That said, much of the fundamental mechanics involved evolve much slower—if it ain’t broke, don’t fix it, I guess. 

One of the basic operations systems required is the Starting System; one of the most critical components therein is the starter solenoid, just like in a car, but what does a starter solenoid do on a motorcycle?

Here’s the Short Answer to What Does a Starter Solenoid Do on a Motorcycle?

A starter solenoid is a switch that completes the connection between the battery and the starter. The solenoid energizes the coil when you push your starter button, generating contact to complete the circuit transferring Direct Current (DC) from battery to starter. 

What Is a Solenoid?

A starter solenoid is a specific length of wire coiled around a two-part core—half immobile and half mobile (the armature). The electrical current passes from the battery through the wire, the resulting magnetism mobilizes the armature, activating the bike’s starter.

The mobile core’s motion towards and away from the stationary center categorizes this solenoid as linear. While linear solenoids are more common in bikes, the movement doesn’t have to be back-and-forth for the piece to be considered a solenoid.

For a component to be defined as a functional solenoid, only three components are required: 

  1. Coiled Wire: Without the coil of wire, the activation process can’t begin.
  2. A Mobil Core: Without a moveable body to move towards and away from a stationary center, all you have is an electromagnet. 
  3. Electrical Charge: Without electricity, the coil of wire is little more than a spring. 

In your bike’s starting system, these parts converge to move the armature, completing the circuit, and, if everything else is functioning correctly, ignite your bike’s motor. Once you let go of your starter button, the solenoid deactivates, forcing the core back to its original post and breaking the circuit. 

Deactivation is just as crucial to your starter’s health as activation-it stops continuous attempts to start the engine after its running, which would fry your starter motor. 

Is a Solenoid the Same as an Electromagnet?

Since the solenoid employs the natural power of electromagnetism, bike riders and mechanics tend to use the term interchangeably. That said, the solenoid is not truly an electromagnet.

Related: Motorcycle Idles But Won’t Accelerate (Solved & Explained)

How Does a Solenoid Work on a Motorcycle?

As the battery surges, the bike’s solenoid generates an electromagnetic field, with which it surrounds the mobile part of the solenoid’s core, the armature. The area moves the armature to complete a circuit, activating your bike’s starter powering that cranks the motorcycle’s flywheel. 

Solenoids are a critical component of a motorcycle’s starting process. Still, they’re a relatively simple instrument to grasp for us newbie bike wrenchers; understanding its function doesn’t require advanced math as much as it does elementary physics.  

  • When the solenoid is at rest, the circuit between the battery and the starter motor is incomplete.
  • Once you press your starter button, the battery surges to energize the solenoid’s coil. 
  • The energized coil creates an electromagnetic field, arching the armature connector into the position required to complete the circuit. 
  • The starter motor is triggered as the circuit completes, initiating the cranks that starts the flywheel’s piston-rotation process. 
  • NOTE: Once the bike is running, it’s essential to replace the starter button; if the solenoid’s electromagnetic field continues to crank the starter motor after the bike is already running, it can damage multiple starter components. 

Can You Start a Motorcycle Without the Solenoid?

You can start a motorcycle without its solenoid by bypassing the coil, using a metal-bladed object like a screwdriver to complete the circuit from battery to starter motor. It might require two people.

How to Bypass the Starter Solenoid

Here’s how to bypass the starter solenoid:

  1. Find the starter motor on your motorcycle.
  2. Find the two metal connectors on the back of the starter solenoid.
  3. Stick the metal blade of an insulated screwdriver across both metal contacts.
  4. Have your assistant push the starter switch and pray the electrical charge travels across the screwdriver from one connector to another. 

Wait a minute, does that mean that you can start a motorcycle without a starter?

Old-school bikers used kickstarters that didn’t use electronics or solenoids at all. Even a modern bike can be push-started, meaning you can bypass the starter system altogether, provided your battery is charged and in strong enough condition, at least sufficient to light your headlight up to its standard luminosity.  

If your battery is functional, you may be able to push-start or pop-start your bike without a starter; not always. 

Related: Motorcycle Clicks Instead Of Starting: 3 Reasons (Solved)

How to Test a Solenoid on a Motorcycle

There are two primary tests you can run to inspect the condition of your motorcycle’s solenoid. Both tests reveal fundamental issues with the part. First, ensure the connector engages and completes the starter’s path. Then, ensure the circuit to the starter is connected and unobstructed when the connector is engaged.

The solenoid or starter relay is just one of multiple starter issues that can impact your faithful steed. 

Troubleshooting starter problems can be a discouraging and lengthy project; below, we’ve included two simple tests you can run on her to at least eliminate the possibility of the solenoid being the culprit. 

Motorcycle Starter Solenoid Test 1

The purpose of this initial test is to notice if the armature is moving to complete the connection between the battery and starter motor.

Step 1

The solenoid includes two wires that generally attach to the starter button. The solenoid doesn’t have polarity; the sides aren’t specific. All you’re trying to do is charge the wire with some current. Using rear probes, connect directly from the battery to one of the solenoid wires, doesn’t matter which, but you still need to attach the negative side of the battery first. 

Step 2

  • Hook a second rear probe onto the solenoid, connecting it to the positive side of the battery. 
  • As the circuit is completed, you’ll hear a loud “click.” That’s the sound of the connector arching up to complete the course. 
  • Suppose you hear the click; congrats; time to move on to the next test.
  • If you don’t hear the click, you’ve got a faulty solenoid on your hands. In some cases, if corrosion is present on the solenoid’s inner connectors, the unit might fail to start even when the connector activates.
  • If you hear the click but the bike doesn’t start, the following test is the next troubleshooting step.

Motorcycle Starter Solenoid Test 2

Once you’ve established your solenoid is clicking, its time to move onto test 2:

Step 1: Maintain your connections placement from the initial test, but detach the rear probe from the positive battery terminal.

Step 2: Hook your multimeter up to the primary solenoid connectors.

Flip your multimeter to resistance-test-mode; remember, polarity doesn’t matter. Clip one of your multimeter connectors to each side of the solenoid. 

Step 3. After you’ve got it all hooked up, your meter display should read something like “OL”: you’re looking for your multimeter to indicate an open circuit. 

Step 4. Hook up the positive side of the battery using the rear probe connection from Step 1. This charges the solenoid, mobilizes the connector, and completes the circuit from the battery to the starter motor.  

Related: 11 Reasons Motorcycles Won’t Push Start (Electric Start)

Can You Replace Just the Solenoid on a Motorcycle?

It’s possible to replace the starter solenoid without replacing the whole starter, though it’s generally not a service offered by pro mechanics. Both repairs require removing and reinstalling the starter, making replacing the entire worn unit a more economical choice. 

General moto-mechanic practice replaces the entire starter unit if the solenoid fails. 

While it is cheaper to rebuild a starter than to replace it as far as parts are concerned, there are particular tools you’ll need access to, a growler, for example, to check the relay’s windings. 

This makes replacing the solenoid a challenging task to perform on your own, even for a decent home-wrencher.

The extra steps also mean labor isn’t much different, should you go to a pro, making the final price difference an insufficient excuse to put a new solenoid into an old starter, as far as most riders are concerned. 

Ok, fine, what is the cheapest way to replace a worn starter solenoid on a motorcycle?

In some cases, home moto-wrenchers claim they fixed a weak solenoid connection simply by flipping the disc around the solenoid, resulting in more solid contact.  

The clicking sound riders tend to hear accompanying their failing starter situation is the sound of the armature arching from the battery’s charge without contacting enough to complete the connection. 

  • Sometimes fixing a faulty solenoid is as simple as refreshing the connectors. Sometimes a refresh can extend the starter’s life for years, postponing the replacement.
  • Still, all starters and solenoids wear eventually, which is why when my solenoids go, I err on the side of replacing the whole starter. If the solenoid is worn on the used starter, the motor could be worn too. 
  • I’d hate to go through the trouble of uninstalling my stater, replacing my solenoid, reinstalling the old starter only to tear it all back apart when the starter motor fails down the road.  
  • Dishing out the cash at the first sign of starter failure ensures the added security of a brand new starter; you can infer that this repair will last longer than replacing the small starter components one at a time as they wear out. 
  • Replacing the entire unit also saves time troubleshooting, as which interior component of the starter is failing becomes irrelevant when you return the starter itself. 

In short, while you can replace a failing starter solenoid without replacing the whole starter unit, it’s not recommended. Replacing the entire starter could save you money in the long run, as the starter needs to be removed to replace its internal components regardless. Replacing them one at a time as they fail ends up being more costly than replacing the whole starter at the first sign of failure.

Sources

How Does a Solenoid Work? | electricsolenoidvalves.com

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