Stators are the unseen component, indeed most riders don’t even know it exists. Without the stator, we going nowhere, a stator is the birthplace of your dirt bike’s ignition system voltage.
All dirt bikes require a stator in order to produce voltage to run the ignition system, in addition, the stator provides power for lights, if fitted, and charges the battery if fitted.
In this post you’ll learn where a dirt bike stator lives and what it does, you’ll learn the symptoms of a faulty stator and finally, you’ll learn how to test a stator using a DVOM.
Where is a Dirt Bike Stator
The stator is fastened behind the left side aluminum cover of your engine (most engines).
It must be located there because it requires both a rotor and the rotating motion of the crankshaft in order to produce voltage.
What a Dirt Bike Stator Does
A stator is responsible for producing the voltage required to run your bike’s electrical system. Even bikes fitted with a battery and electric start only use that battery power to crank over the engine. As the bike starts the stator takes over responsibility for all the electrical demands, and in addition for battery-fitted bikes, the stator must also charge the battery, replacing spent voltage during the starting process.
But no matter if your bike has a battery fitted or not, it will require voltage to run the ignition system (fire the spark plug), and that’s the stator’s job.
So the stator is a really critical component, no stator means no spark plug activation and means no fun!
How Does it Work?
The stator consists of multiple coils of copper wire (bikes where a battery is fitted, coils are typically grouped together into three circuits) arranged in a circle and attached to the backside of the left engine side cover. When the side cover is fitted to the engine, the stator coil arrangement fits neatly inside a cavity on the rotor.
The rotor is fixed to the crankshaft and rotates as the engine is kickstarted or cranked over with the starter. As the rotor spins, magnets attached to the inner surface pass over the stationary stator coils and this excites the coils and produces voltage.
The voltage is however alternating current (AC) and must be converted to direct current (DC) before a dirt bike electrical system can make use of it. And to perform that function your bike is fitted with a rectifier. It rectifies the voltage, meaning it converts it from AC to DC.
For bikes fitted with a battery, a rectifier with an integrated regulator regulates how much voltage goes to charge the battery. Too little is no good obviously but too much is bad also, a faulty regulator will kill a battery by overcharging it.
Your bike’s stator likely also incorporates the pickup (most do). The pickup has a special function, it signals the CDI or ECU when it’s time to fire the spark plug.
A new stator will come with a new pickup.
Common Faulty Dirt Bike Stator Symptoms
Stators work hard, you already know that, so you won’t be surprised to know they fail regularly. Here are some common symptoms associated with stator failure.
- No start
- No start when hot
- Engine stalls when warm
- Engine misfiring
- Engine backfiring
- Engine won’t rev
- Engine no power
- Engine black smoke
How to Test Dirt Bike Stator
To test a dirt bike stator we have a couple of options. However, if our dirt bike isn’t running we have only one option open to us, the Static test. Let’s take a look at both of these right now and how to execute them like a pro.
You’ll need a DVOM tool in order to run these tests and you can check out the DVOM I recommend here on the AV tools page.
Dynamic Dirt Bike Stator Test
This test will suit you if your dirt bike runs and idles, conversely if your bike doesn’t run you’ll need to jump on down to the static test below.
In the dynamic test, we’ll unplug the stator wiring block connection and we’ll check AC voltage with the engine running (2500 rpm) using our DVOM.
The dynamic test is as follows:
Locate the stator block connector and disconnect.
With DVOM set to AC (~) voltage and the bike running check:
- A to B
- A to C
- B to C
As per the picture, typically the AC voltage reading between 15 and 60. Depending on spec and rpm, but check your makers’ spec.
Static Dirt Bike Stator Test
The static test suits a running dirt bike or a nonstarter just the same. For this test, we’ll use a DVOM set to resistance (Ω). We’ll be checking continuity in the circuit.
Continuity simply means we’ll be checking for broken wires within our copper coils. To do that, we’ll disconnect the stator wiring block connector. We use the DVOM to send a small charge through one terminal using the positive probe, and using the negative probe on a second terminal, we read how much of that voltage actually makes it through (if any).
The static test is as follows:
With the DVOM set to resistance (Ω) and the stator plug disconnected, measure the following:
- A to B
- A to C
- B to C
Typically a reading between .1 and 1 Ω is OK but check your makers’ spec.
In addition, we can check for a short to ground. With the DVOM set to resistance (Ω) and the stator plug disconnected, measure the following:
- A to G
- B to G
- C to G
No continuity means there’s no short.
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