Electrical gremlins can be difficult to tame, but you’re in the right place.
An ATV will not start with a bad stator, the engine requires electrical current from the stator to power the coil and fire the spark plug. Symptoms of a faulty stator may include:
- No start
- Intermittent start
- Hot start issues
- Fouling plugs
- Flat battery
In this post you’ll learn how a faulty stator effects your ATV, how to test it and how to fix it.
It is possible for the engine to start if the stator is failing however, it all depends on how it’s failing. A intermittent failing stator will cause the engine to run like a pig or not at all.
An inconsistent voltage supplied to the coil will result in:
- Misfiring plug
- Black smoke
- Fouling plug
You get the idea!
What Does A Stator Power?
There are two flavours of stator, single or 3 phase. The 3 phase being most common. Each phase of the stator is comprised of copper wire wound around an iron core.
The stator is fixed to the engine and as the flywheel with magnets attached rotates around the coils, voltage is created.
All engines need electrical current in order to function. Even an ATV without lights, battery or starter motor needs voltage to power the coil. And the coil transforms voltage into a spark at the plug.
More sophisticated ATV’s will have larger demands – battery, starter motor, dash lights, sensors, coolant fan, lights, winch etc.
While your ATV may have a battery, all voltage is ultimately provided by the Stator.
On most ATV’s, battery power is used to operate dash lights and crank over the engine. The cranking flywheel excites the stator and generates voltage to power the coil via the CDI box (Capacitor Discharge Ignition).
After start, the Stator provides all the power required, including topping up the battery voltage spent cranking the engine.
How To Test The Stator
Stators do a very important job and are under a ton of stress, so you won’t be surprised to learn they fail all the time.
Common stator problems:
- Open circuits
- Damaged or corroded wiring
- Power-washing – over doing it with the power washing is a common root cause of problems, it forces water in and can short out circuitry or cause corrosion
- Flywheel fault – magnets falling off is popular with some brands
- Wiring loom – rodent damage
- Block connectors – loose/corroded block connectors
Two tests are common:
- A Static Resistance Test (engine off)
- A Dynamic Voltage Test (with engine running)
You’ll need a volt meter (DVOM) and you’ll need to access the stator wiring loom. It’s easy to locate, as its the loom that exits the engine side cover, follow the loom to its connector and disconnect it.
You’ll be testing the stator/engine loom side, and as your engine probably isn’t running, we’ll perform the static test first.
Static Resistance Test
This is a two part test, and both are simple to execute. we’ll begin by locating the stator wiring loom block connector. It may contain three wires or more, you’ll be looking for 3 identical wires or 3 wires grouped together.
Lets name them a, b and c, it doesn’t matter which.
- Set the DVOM to read resistance.
- Using your meter, read resistance between a and b, b and c and finally a and c.
- The reading should be in the region of .1 to 1 ohm. Each manufacturer will have their own spec. But as a rule of thumb, resistance should be low and should not read open.
An open (o/l) meter reading on one phase is the most common result when testing a faulty stator.
Testing short to ground
This is the second part of the static test and is easy.
- Place the ground probe on chassis ground
- Probe a, b and c in turn
- All should read open circuit
Any reading on the meter means you have a short to ground and a faulty stator.
2 Dynamic A/C Voltage Test
The dynamic test will require a running engine, and so may not suite all readers. Note the reading of voltage in this test is A/C (Alternating Current), not the more common D/C.
- Set your meter to read a/c voltage
- Place the black probe on chassis ground
- Place the Positive probe on each wire a, b and c in turn
A reading of 15 to 30 volts a/c can be expected, less or none equals a faulty stator.
Fitting a Stator is straight forward but you’ll need a special crankshaft tool, and it may be engine specific.
To replace the Stator:
- Remove side cover – may need to remove gear selector foot rest etc
- Remove the side cover – unfasten bolts in star pattern to avoid straining the cover
- Loosen flywheel nut
- Using fly wheel puller, pull flywheel
- Remove nut and remove flywheel – be mindful of key
- Remove the stator fasteners & remove stator
Align the flywheel key-way with the crankshaft key and torque to specification. (You’ll need a piston stop tool). Incorrect torque can cause the flywheel to come loose or over-tightening can crack the flywheel.
Ensure the wiring isn’t pinched by side-cover and grommet fits correctly.
Replace the side cover gasket and torque to spec and in a star sequence.