Village Science - Teacher Edition


Snowmachine Clutch

Teacher Edition Contents

Skill, Tools, & Craftsmanship

Cutting & Drying Fish
Nails, Pegs, & Lashings
Falling Trees &
     Small-Scale Logging
Chainsaw Clutch & Chain
Ice Pick


Wood Stoves
Wall Tents
Insulation & Vapor Barriers
Gas Lamps & Gas Stoves


Piloting A Boat
Boat Design
Magnetos & Spark Plugs
Outboard Motor Lower Unit

Outboard Motor Cooling System
Snowmachine Tracks
Snowmachine Clutch
Winter Trails


  1. Remove the clutch guard from a machine and identify the parts.

  2. Block the back of the machine up or suspend it so the track is free from the ground. With students at a safe distance, start the engine. Accelerate and decelerate the engine. Can you see the clutch responding automatically to the throttle changes?

    Make sure no one is in front of the machine, and no one has loose clothing of any kind.

  3. Watch the drive clutch. Is it bigger at low or high rpm?

    It is bigger at low rpms.

  4. Watch the driven clutch. Is it bigger at low or high rpm?

    It is lower at high rpms.

  5. Is clutch movement smooth or erratic? If it is not smooth, what does this indicate?

    If it isn’t smooth, it indicates poor lubrication.

  6. At below zero temperatures, put polar grease between your fingers on one hand and regular grease between the fingers of the other hand. Can you feel the difference?

  7. What would slip if the track were frozen down and the engine accelerated? Do you see evidence of this around the clutch?

    The belt burns. Fine pieces of belt are all around the clutch.

  8. Remove and replace a drive belt. Compare a worn and a new belt for width. Find the price of a new belt.

  9. Can you see the weights in the drive clutch? If this isn’t possible, try to find an old one that has been taken apart. Describe how inertia causes the drive clutch to close together. Draw what you imagine happening.

  10. Compress the spring from both the drive and driven pulleys. Are they stronger or weaker than you thought? Is there a way to tighten the spring on the driven pulley on the machine you are looking at?

    The spring on the driven pulley should be much stronger than the one on the drive pulley. Most driven clutches have a way to tighten or loosen the spring.

  11. Improvise some pulleys, even if you have to use a rubber band as a drive belt. Use different size thread spools as pulleys if you can’t find anything else. Predict how many turns the driven spool will turn when the drive spool turns once.

  12. Drive a four-wheel ATV, accelerating through the gears. While doing this, try to imagine what would be happening to the drive and driven pulleys if it had a snowmachine clutch. (Actually, Polaris six-wheelers have a clutch like a snowmachine.)

  13. Do you think this kind of clutch would work on an outboard motor, giving better performance?

    I have always wondered this. It might help, but it would be heavy and bulky.

Student Response

  1. How do each of the following attempt to balance the engine speed with the load?

    • Trucks, cars & four-wheel ATVs:

    • Outboard motors:
    Changing props

    • Airplanes:
    Variable speed props

  2. What are the three main parts of a snowmachine clutch?

    Drive clutch, belt, and driven clutch

  3. Which clutch is on the end of the engine’s driveshaft?

    Drive clutch

  4. Draw a picture of a big pulley driving a smaller one. If the big pulley turns once, will the little one turn more or less than one turn?

    More than one turn

  5. Draw a picture of a smaller pulley driving a bigger one.

  6. Draw a picture of two pulleys of the same size.

  7. Which of the above pictures illustrates an engine starting to move?

    Smaller driving the larger

  8. Which one of the above illustrates an engine at cruise speed?

    Same size pulleys

  9. What is the main advantage of a snowmachine clutch over a truck transmission?

    It is constantly sensitive to the load.

  10. Why couldn’t a snowmachine clutch be used on a truck or car?

    A belt cannot drive the power required to move a car.

  11. What is the advantage of a snowmachine clutch over a chainsaw clutch?

    A chainsaw clutch is like a one-speed transmission.

  12. What is the governor on an engine? What happens if there isn’t enough load on an engine? What happens if there is too much load on an engine?

    The load is the governor. If there isn’t enough load, the rpm are too high and the machine is stressed by the inertia of the piston. If there is too much load on the engine, it is again stressed, but this time from the pressure on the parts.

  13. What two things does the snowmachine clutch balance?

    Centrifugal force in the drive clutch and the spring pressure on the driven clutch

  14. Why is good lubrication important in a snowmachine clutch?

    So the centrifugal force and pressure of the spring can be in balance and friction between parts will not interfere with that balance


  1. A pulley 3” in diameter turns a pulley 2” in diameter. If the first one turns 50 complete revolutions, how many revolutions does the second one turn?

    75 revolutions

Questions or comments?
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