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Gearbox slipper clutch test

Roger Lee

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The gearbox slipper clutch test is done at every inspection.


Here are the basics and you may not be the one doing this, but at least you'll have an idea on the how.



If you have a 912ULS 100 HP with the slipper clutch then you absolutely should be doing this simple slipper clutch test as out lined in the Line Maint manual at every inspection. It takes all of 10 minutes and it is vital to the health of your engine and especially your gearbox. Normal slipper clutch torque is usually between 440-490 in/lbs. If you get down to around 350 in/lbs or lower I would personally get the Bellville washers changed and re-shimmed. The higher the number the better. The max is 540 in/lbs.


This is an easy check and there is absolutely no reason not to do it. If you are getting kick back this may be the cause.


Here is the simple explanation:

First lock your crank shaft with your crank shaft locking pin screw. Mark out from the center of the prop hub 24"- 30". If you measure too close to the prop hub getting a steady good reading is too hard. Put your scale on your mark and pull down until it stops. Look at the number of pounds it takes to pull the prop through while it is moving. Now multiply that number by the number of inches you came out from the hub center.




30" out from the center of the prop hub and your pounds on the gauge was 15.


30" X 15 pounds = 450 in/lbs




26" out from the center x 18 gauge pounds = 468 in/lbs


I have attached the Rotax pages for this test below.



If you need to have a gearbox re-shimmed or have a prop strike and need the mandatory gearbox inspection I will be happy to do it. If you have a prop strike and before you pull the gearboxplease call me first.

Slipper clutch test.pdf

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