Basics of the Snowmachine Clutch

Diagram from The Gates Rubber Company

  • A snowmachine clutch actually consists of two separate clutches connected together by a rubber belt.
    • The primary clutch is connected to the engine's crankshaft
    • The secondary clutch is mounted on the end of the jackshaft (which connects to the drive shaft via a chain and gears).
  • The primary purpose of the clutch is to smoothly transmit power from the engine to the jackshaft and to remove the connection when the engine is idling so that the machine is not always rolling.  
  • This type of system is also referred to as a continuously variable transmission.  It is called this because as the engine speed increases the final drive ratio increases.  That is, the difference between the engine speed and track speed decreases.  It is equivalent to an automatic transmission on a car with an infinite number of gears that you never felt shift.  Let's take a look at how this "infinite gearing" process works:
  1. At idle the primary clutch just spins and does not "grab" onto the belt.  As engine RPM (revolutions per minute) increases to engagement speed (the RPM where the snowmachine starts moving), the primary clutch begins to pull together and start squeezing the belt.  
  2. Now the belt is turning. This makes the secondary clutch turn, which causes the track to turn and the snowmachine to move forward.  
  3. As engine speed increases above engagement, the primary clutch squeezes together some more and pushes the belt so that it moves to a larger radius on the primary.  Because the two clutches rotate about fixed points, the belt gets pulled into the secondary, spreading it farther apart and moving the belt to a smaller radius.  

  • To make the above movie play, double click it.
  • Note that the primary clutch (on the left) never stops spinning, but the secondary (right) does stop spinning at idle speeds.
  • In case you are curious, the engine rpm got up to about 7000 rpm and the track speed got up to about 60 mph or more during this clip.  I supported the track with a stand and ran the throttle while an observer ran the camera.
  • It's at this point I should make a comment about not trying this at home.  As the manufacturers state, you should never operate the engine with the clutch guard removed or the hood up, and especially not both at the same time!
Image taken from

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