By definition, a clutch is a coupling used to connect and disconnect

the driving and driven parts of a mechanism. Modern motorcycles

and ATVs require the use of a clutch to connect and disconnect the

engine (driving) and transmission (driven). Without the clutch, there

would be no way to stop the vehicle from moving without also stopping

the engine. The clutch also makes shifting easier and minimizes

stress on gears and other components, extending equipment life.

Why a Wet-Clutch?

The clutch is a frictional device, meaning it requires friction to complete

the task of connecting the engine and transmission. Because

a clutch is a frictional device, and one of the main purposes of a lubricant

is to reduce friction, why would anyone introduce an oil to a

clutch? Modern technology and superior technological know-how

have afforded the ability to formulate multifaceted lubricants capable

of functioning in a variety of conditions. While not all lubricants

are suitable for use in wet-clutch applications, an oil-immersed

clutch benefits from the lubricant’s ability to reduce operating temperatures,

prevent the formation of deposits and clean internal

components. All of these benefits lead to better performance and

longer life.

Clutch Slip

Clutch slip is a big concern with many powersports enthusiasts. To

the operator, clutch slip feels like an elongated shift or a delay in the

transfer of power from the engine to the wheels. This is due to a lack

of friction generated within the clutch pack.

The clutch pack is located between the clutch’s inner hub and the

clutch basket and consists of a series of two types of plates: steel

and frictional. The inner-most plate is a plain steel plate (sometimes

aluminum) which attaches to the inner hub via tabs on the plate’s

inner diameter, and the inner hub is connected to the transmission.

The next plate is a frictional plate which attaches to the clutch

basket via tabs on its outer diameter, and the basket is attached to

the engine. The frictional plates are coated with a fibrous compound

that helps them grip the steel plates when the clutch is

engaged. The plates within the pack alternate until the desired

pack height is reached.

A spring-loaded pressure plate atop the clutch pack applies

constant force to the clutch pack. The mechanical device that

engages and disengages the clutch assembly, normally a lever

located on the handle bars, pulls the pressure plate back and allows

the plates within the clutch pack to separate, severing the connection

between the engine and transmission.

The clutch is only disengaged in order to stop the transfer of power

from the engine to the wheels. When engaged, the clutch spring

applies a constant load on the pressure plate, forcing the clutch pack

together. The load creates a high level of static friction between the

plates in the pack, causing them to rotate together. In this position,

rotational movement from the engine is transferred to the clutch

basket, to the frictional plates, through the steel plates, into the inner

hub and finally to the transmission input shaft. The key here is the

static friction that holds the frictional and steel plates together,

allowing the transfer of power from the engine to the wheels. Clutch

slip occurs when this static friction is overcome and the plates

rotate at different speeds, or slip.

Common Causes for Clutch Slip

While it seems logical to blame the lubricant for clutch slip, there are

many possible causes. Worn frictional plates, glazed clutch plates,

loss of clutch spring tension, improper clutch pack height, engine

modifications, operator error and the use of an incorrect lubricant all

are potential causes for clutch slip. If a lubricant with the correct frictional

properties is used, it is the least likely cause of clutch slip.

Wet-Clutch Compatibility

Wet-clutch compatibility is determined through standards set forth

by the Japanese Automotive Standards Organization (JASO) and

the International Organization for Standardization (ISO). Both standards

categorize oils according to their frictional properties, allowing

consumers to choose the appropriate oil based on which JASO

or ISO category is recommended by the equipment manufacturer. If

no JASO or ISO category is listed on an oil, it is likely that compatibility

in wet-clutch applications has not been reviewed. These oils

should not be used in wet-clutch applications.

AMSOIL and Wet-Clutch Compatibility

The frictional characteristics of all AMSOIL powersports oils have been

fully reviewed using the test methodology set forth in JASO standard

T903:2006 sub-standard T904 and ISO standard 24254:2007. While

clutch slippage and wet-clutch compatibility are major concerns, it

is important to choose an oil that provides maximum protection

and performance for other lubricated components as well. A good oil

must not only offer the necessary frictional properties, but also

minimize operating temperatures and reduce the formation of varnish

and lacquer. A good oil must also maintain plate cleanliness, provide

good anti-foaming properties and superior shear stability.

These are characteristics offered by all AMSOIL motor oils for powersports

applications.

According to AMSOIL Technical Product Manager, PowerSports

Dave Anderson, choosing an oil that provides balanced protection is

paramount. “Different pieces of equipment have different appetites

for fluids,” said Anderson. “In order to obtain the best performance

for any piece of equipment it is important that the fluid is formulated

to address the main concerns for that application. That is one of the

key reasons AMSOIL provides the variety of products it does.”

Anderson said testing is the key to ensuring AMSOIL products excel.

“Our desire is to provide the best possible performance we can technically

provide,” said Anderson. “Many AMSOIL powersports products

are very application-specific because, from a technical

standpoint, that’s the only way we can provide the highest level of

performance possible.” For more information regarding wet-clutch

performance, refer to the AMSOIL Technical Service Bulletin Wet-

Clutch Operation and Lubrication Requirements in the Dealer Zone

at www.amsoil.com. For more information regarding the performance

characteristics of AMSOIL Motorcycle Oils, refer to the AMSOIL

white paper A Study of Motorcycle Oils (G2156).