650 Clutch Info

The clutch is shown in the Service Manual on pages 3-16, 3-38 to 3-42, and again on 3-68.

Summary

The Burgman 650 clutch is a wet clutch very similar to a conventional motorcycle. As components of the clutch spin faster with increasing RPMs from the engine, they are forced not only outward but also inward. This inward motion forces the clutch plates together, thereby engaging the clutch.

Introduction

The Burgman 650 uses a "roller and ramp" centrifugal clutch design. This type of clutch is also used in jet skis and helicopters. The 650's clutch differs from the Burgman 400 in that the 400's clutch is dry and located in the rear wheel hub. It functions similar to a drum braking system but in reverse. As the input spins with higher RPMs, shoes are forced out against the bell and engaging the rear wheel.

The pathway of the drivetrain is: Engine > CVT > Clutch > Transmission > Final Drive > Rear Wheel

Location of the 650's clutch.

Clutch Plates

There is a stack of five clutch plates that must be forced together to engage the rest of the drive train, or forced apart to disengage the rest of the drive train. These components are identical to a cable-actuated clutch in a conventional motorcycle. When the clutch is disengaged, the clutch plates are separated from each other by concave washers.

Clutch Oil

The clutch is a type of "wet clutch" that uses oil to lubricate the clutch plates especially when the clutch is in a slipping operation. The oil must not be "energy conserving" or else it will negatively affect the clutch plates' ability to engage each other with friction. The clutch shares oil with the engine but is actually a separate entity that must have oil piped to it via an oil hose and oil return (see figure below). Although the clutch is separated from the transmission only by a gasket, it is likely that the reason the clutch requires engine oil is that it is under pressure and can be injected where it is needed. The transmission only uses the splash lubrication method that is likely to be insufficient for the clutch. The clutch cover has a prominent external raised area that terminates at a bolt. This feature channels oil to the middle of the clutch basket where it is injected onto the clutch plates. The oil also goes through its own sump filter before it returns to the engine's main oil pan.

Clutch Hoses	Clutch Oil Pathway	Oil Schematic

Roller Description

There are a total of 54 rollers arranged in a circle, in 18 groups of threes (figure below). These rollers are directly responsible for engaging and disengaging the clutch plates. The roller's positions dictates the engagement of the clutch and the degree of that engagement.

Roller Operation

The rollers sits in the clutch basket, and the clutch basket is fed directly from the CVT. When the engine is off or there are insufficient RPMs, the rollers are kept at the bottom of what is essentially an inclined plane (figure below) with spring tension pushing them down. The inclined plane is the "ramp" of the "roller and ramp" centrifugal clutch design. The ramp is arranged so that as the roller goes up the ramp, the roller is also forced inward towards the middle of the bike. As the roller moves inward, it pushes against the "inner plate" (figure below). The inner plate pushes against all of the clutch plates and thereby engages the clutch and transmits power to the rest of the drivetrain. The rollers can go up the ramp only when there is enough centrifugal force (i.e. higher RPMs) to overcome the spring tension forcing the rollers down.

Clutch Diagram	Roller Operation

Sources:
http://burgmanusa.com/forums/viewtopic.php?p=408345#p408345
http://burgmanusa.com/forums/viewtopic.php?p=408247#p408247
http://burgmanusa.com/forums/viewtopic.php?p=192138#p192138
http://burgmanusa.com/gallery/Jims-Gallery/Clutch/

Clutch Topics:
http://burgmanusa.com/bkb/650+Transmission-Clutch

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