How Does a Polaris Primary Clutch Work?

Harvey repairing a primary clutch

How Does a Polaris Primary Clutch Work?

MARCH 31, 2022

You know the feeling of a good clutch engaging. You twist the handle or drop the pedal and your ride revs and blasts forward. Suddenly you're ripping through the woods, no shifting required. If you're like Harvey, you dig the speed and power that comes with a Polaris ATV, but hold as much appreciation for the screaming metal precision that makes the ride work. 

The Polaris primary clutch is one of the most crucial and intricate parts of your ATV, but the mechanics behind it are basic physics — leverage, resistance, mass, and centrifugal force. 

In this article, we’ll explain the different parts and functions of an ATV primary clutch. 

The Polaris Primary Clutch - Introducing the CVT

In a standard clutch, the vehicle will start in one gear and then shift to a second gear when the rate of acceleration outpaces rotations per minute (RPMs).

The Continuously Variable Transmission (CVT) can be best explained as a gear changer without gears. It may seem like a new design compared to manual gear shifts, but its core concept can be traced back to sketches from Leonardo Da Vinci.

 In 1879, Milton Reeves built the first true variable-speed transmission to use in a sawmill engine, later adapting it for use in cars. His design went on to inspire friction belt CVTs, which have evolved into the systems our ATVs run on today.

Unlike a manual or automatic transmission, there are no gears to shift and no tangled hydraulic systems. There are three major components of a Polaris CVT: theprimary clutch, the belt, and the secondary clutch

How does a CVT clutch work?

Instead of shifting gears to change the ratio of RPM to acceleration, the CVT actually adapts its shape to stay “in gear.” The belt connects the primary and secondary clutches, resting between two convex metal plates on each clutch called sheaves.

As RPMs increase, the sheaves on the primary clutch close in on the belt and engage it through friction, starting the drivetrain. The belt rides up the tapered faces of the sheaves, moving outward and effectively creating a larger “gear.” The secondary clutch responds in mirrored image, picking up the belt’s slack as the plates shift.

Polaris Primary Clutch Springs

Of course, without any resistance, you would slam open the clutch up all the way each time you revved the gas. That’s 0-100 with no control, which is gonna make for some rough riding.

To compensate for this, a powerful spring holds the primary clutch open. It pushes back against the clutch side sheave, held by a clutch cap. This keeps the shifting of the sheaves and weights to a controlled rate.

Polaris Primary Clutch Weights

The flyweights — also called shift weights or arms — are pinball-flipper-shaped metal wedges mounted on pins to the movable sheave. Often they will have smaller adjustable weights attached to them for fine-tuning purposes. These weights are responsible for the movement of the mobile sheave toward the fixed sheave. Flyweights work, in effect, to counteract the pressure from the spring and determine the rate at which the sheaves close.

When the clutch spins, the centrifugal force created pushes the weights away from the center of the clutch, and applies force to matching rollers mounted on the immobile part of the clutch called the “spider.” Creepy. This in turn compresses the mobile sheave to the fixed, and hey presto, we’ve got traction.

Centrifugal Force?

Centrifugal force is an outward force on an object generated by circular movement. This is not to be confused with centripetal force, which keeps objects moving in a circle with an inward pull. The difference is primarily one of perspective, as the same force can act in both ways depending on whether you’re observing the rotating system from inside or outside. 

Polaris Clutch Balancing

If your clutch isn’t properly balanced, you’ll notice. Your ride will vibrate and rattle, and may start to unthread bolts. As such, it’s critical to your vehicle’s health to keep your clutch in proper operating shape. 

Luckily, clutches will come properly balanced from the factory or manufacturer, and won’t just come unbalanced. Your clutch will only encounter this issue if reassembled incorrectly or damaged somehow. If you’re installing one of our Mother Clutchers, you can rest assured that it’s been properly balanced and checked by top-notch ATV professionals.


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Fine Tuning a Clutch

Clutch springs and arms are precision parts, capable of fine tuning to hit the RPM sweet spot. 

If you’re replacing your clutch with a Harvey’s ATV Mother Clutcher, you won’t need to worry about fiddling with springs or weight arms. Our team members take care of the details. Your new parts come ready to bolt on and ride.

Need a puller tool to remove a belt from your CTV? We sell a heat-treated hardened steel model coated with zinc for corrosion resistance. 

The primary clutch is at the front of your drivetrain for a reason — you’re not getting anywhere without it. Ready to refresh your ride? Check out our clutches here.

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