Pressure Plate

The moving part of a typical motorcycle clutch assembly that, working against clutch spring tension, releases the clamping action on the clutch plates when the clutch lever is engaged.

Panic-brake

An emergency stop, requiring hard, effective controlled brake application, so called because it is often conducted during a moment of panic.

Piston Skirt

The part of a piston that is below the bottom piston ring and piston pin boss. The skirt acts as a guide as the piston goes up and down in the cylinder. It is often the part that shatters when the piston-to-cylinder clearance becomes excessive allowing the piston to rock in the bore.

Parasitic Draw Test

A diagnostic test used to check the electrical system of a motorcycle for current flow (amperage) when the key is off. The purpose of this test is to ascertain whether the battery is being drained while the vehicle is not in use. Some devices with memories such as clocks, radios and digital odometers draw a [...]

Pilot Air Screw

A screw mounted on the side or bottom of a motorcycle carburetor that allows adjustment of the air/fuel ratio in the pilot circuit of a slide type carburetor. Also known as the idle air screw or the low speed air screw.

Parallel Circuit

A very common way of wiring the different circuits on a motorcycle where current is provided to each electrical circuit independently of the others. The failure of one circuit does not affect the rest of the circuits.

Preload

In terms of motorcycle and ATV suspensions, spring preload is the static length of a spring (as it is installed in a motorcycle fork or shock) subtracted from its free length (as it is uninstalled). The spring preload determines the motorcycle ride height and sag. In motorcycle forks, preload is adjusted by the use [...]

Progressive Spring

Progressive springs are often utilized in motorcycle front forks and rear shocks. These springs provide progressively firmer resistance as they are compressed which helps prevent the bottoming out of the suspension. A careful inspection of a progressive spring will reveal that the coils are more tightly wound on one end than the other. The more [...]

Premix

Two-stroke engines require a mixture of fuel and oil called premix in order to maintain proper lubrication. Two stroke engines burn this oil that is mixed with the fuel, which is why two stokes typically smoke out the exhaust pipe. Most motorcycle manufacturers are dropping their two stroke models due to the difficulty in meeting [...]