Motocross clutch – the link between engine and gearbox

How a motorcycle clutch works

The clutch’s job is to disconnect the engine from the gearbox, or connect them again. Pulling the clutch lever interrupts the connection between engine and gearbox. Releasing the clutch makes it possible to connect the engine and gearbox.

To understand this better, it helps to know the role of the individual components:

The friction plates are driven by the clutch basket (via the outer slots), which in turn is driven by the crankshaft. The steel plates, on the other hand, drive the clutch hub (via the inner slots), which then drives the gearbox. The steel plates have no contact with the basket, and the friction plates have no contact with the hub.

When the clutch is pulled, a mechanism is actuated that pushes the pressure plate away. The springs are compressed, and the steel and friction plates no longer touch each other. The crankshaft can therefore no longer drive the gearbox.

When the clutch is released, the springs relax and press the pressure plate back on. The friction plates then contact the steel plates to drive them and rotate the hub / carrier, which can then drive the gearbox.

The materials used on the friction plates therefore have a high friction coefficient to ensure adhesion between the plates.

Motorcycle clutch and engine tuning

When power increases, the clutch needs to be adapted accordingly. A low-quality clutch will not be able to transmit the power correctly, and even if it does not slip, it will wear out extremely quickly.

To counter this, there are various solutions: reinforced friction materials on the friction plates, stiffer springs that apply more pressure to the pressure plate and plates, or a larger complete unit with more friction and contact surface (greater number of plates and springs).

Note: The explanation above is easy to observe on motorcycles – a small 50cc motorcycle has a small clutch with 4 or 5 friction plates and usually 4 springs. A 450cc machine has a large clutch with 7 or 8 plates and 5 or even 6 springs.

Recommendations:

Rekluse and Hinson, two American brands, offer complete clutches and reinforced clutch plates for most motocross motorcycles on the market. Rekluse in particular offers clutch kits with a significantly higher number of plates than standard (up to 12). They even offer a reinforced and automatic clutch system (centrifugal principle) that prevents the engine from stalling.

Identifying faults and wear

Before looking at the clutch’s internal components, it is worth checking the clutch actuation. If the clutch lever becomes stiff, it may simply be that the clutch cable is frayed and no longer slides properly in its outer sheath.

The lever and cable can also indicate the condition of the clutch plates. Explanation: with a new clutch and correct cable tension adjustment, there is a little play. If this play decreases and the cable needs loosening to restore it, this is a sign of potential wear.

Of course, this rule does not apply to motorcycles equipped with hydraulic clutch.

Otherwise, one of the main symptoms of wear is that the clutch slips almost constantly. When the engine revs up, it screams, but it feels like riding with a foot on the brake or with the clutch slightly pulled; top speed is no longer reached.

Tip: To keep the clutch operating smoothly, it helps to lubricate the cable (inside the outer sheath). There are special tools for lubricating cables with lubricating spray. To protect the plates, regular gearbox oil changes are carried out at least at the intervals recommended by the manufacturer, and high-quality oil is used.

Motocross clutches in our shop:

In our online shop, everything needed to service, repair and upgrade the clutch of a motorcycle can be found. Complete clutch kits are available, both OEM quality and reinforced, as well as all clutch components individually: springs, clutch baskets, inner hubs, plates, etc. These parts are stocked from well-known manufacturers such as Rekluse, Hinson, Moose Racing or Prox, and of course for popular models such as KTM EXC, KTM SX, Yamaha YZ, Honda CR, etc.