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Rotax Gearbox Inspection Time Table

Roger Lee

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Hi All, smile.gif


Here is a reminder about our Rotax gearbox inspection time table. There are many getting close or already there so make sure you get this done when it is due. It is a requirement. The only one who can do a gearbox is a "Heavy Maint" rated mechanic. You do not want your backyard mechanic to mess this up. You also need a special tool to compress the gear set down and a hydraulic press.


If you have a 912ULS mfg. after 2003 with a slipper clutch then the inspection is at 1000 hrs.

If you have a 912ULS and use 100LL more than 30% of the time then the inspection is at 600 hrs.

If you have a 912UL (no slipper clutch) then the inpsection is at 600 hrs.

I'm sure the rates to do this will differ because of labor cost at each facility. To clean the clutch of the lead if you have used 100LL then it will be approximately $100 + shipping from the distributor. You do not necessarily need new bearings, but if you choose to add that as an option it is about $160 in parts and another $100 in labor.

All you really need is new Bellville washers ($60) and shimming. If you need only the inspection then you are looking at roughly 2.5 hrs labor plus the $60 for the washers. This should be all most of us need. You can have the shop at your location do it right there or send the gearbox out. Shipping the gearbox is quite easy. If you have any questions you can call me or Jeremy at CPS. Jeremy can do these inspections at CPS and I'm also Rotax Heavy Maint rated here in Tucson.


If you are an owner that blends their fuel with a 50/50 mix of 100LL and 91 oct. then your due at the earlier times.


If you use 100LL then you will also have to send the slipper clutch in to one of the distributors (CPS, Lockwood or Leading Edge) to have the clutch dismantled and cleaned of the lead paste that will render the clutch either inoperable or greatly inhibited.


There is nothing really good to be said for 100LL and if your aircraft can use 91 oct. unleaded regardless of the ethanol or not, then you are way ahead of the maint game and it saves you a lot of money, even from day one starting with low time oil changes.

Gearbox Inspection Time Table.pdf

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Hi Roger F,


Are you referring to the gear set replacement / recall? That wasn't an inspection just pull out the first gear in the box and the one on the crank for replacement. This wan't an inspection.

This one is based solely on total hours of use because of wear at that stage. You need to get the bellville washers replaced at this time and re-shimmed. The max friction torque test measurement is 540 in/lbs. I don't see anyone getting to that number, but should be up in the higher 400's. The higher the better in this case. I have never seen one over 500 in/lbs.

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  • 2 years later...

Hi Roger. The Rotax manual shows the normal range for torque to turn past the clutch is 22 to 44.3 ft. Have you, or any others here, worked on a CT that had "low torque" around 24 ft.lb.? If a CT might have low torque such as this, does it result in any noticeable problems/vibrations?

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Just so everyone is on the same page we are talking about the friction test for the gearbox when the crankshaft locking pin is in place. You measure out from the center of the prop hub any where from 26"-30" and place a scale at that mark and pull through the 30 degree free moving arc. You really don't want to measure out less than 26" because it makes it too hard to pull the prop through and get a steady number to use, but it can be done. When you get that number it is in ft/lbs. Could be something like 17 ft/lbs. Then you multiply that number times the distance you measured out from the hub center.


i.e. 28" x 17 ft/lbs = 476 in/lbs. This should be done at 100 hr. and annual inspections and written down on the check list and most definitely in your logbook. Unfortunately I rarely see this. How does anyone know what the last one was or see the trend. Poor documentation to be sure.


The in/lb limits are 264 in/lbs up to 531 in/lbs. The higher the better. Normal usually ranges from 400 in/lbs to 485 in/lbs. (most are 440-480)




24 ft/lbs or 288 in/lbs is way too low. Time for a re-shim. If it is that low run the engine and warm it up and try one more time. If it is still that low re-shim and this would include 3 new bellville washers because that is most likely the problem or the plastic spacer disintegrated.

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Roger, a small error in units, I think. When you measure the force to pull the prop (with crank locked) you get a value in pounds (not ft/lbs, as you wrote). You then multiply that value by the distance in inches from the hub to get inch pounds.


So, your calculation should be: 28 inch x 17 pounds = 476 inch pounds (not inch/pound).



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This is what I came up with some time ago for my annual checklist:


Correct friction torque: 22 to 44.3 ft/lbs (11 to 22 lb pull at propeller station of 24”)


That would be correct, right?


I measure 2 feet out, protect the prop with a rag, and pull and measure the pounds indicated when the prop moves. Between 11 and 22 pounds and I'm good to go. And I write it on the checklist.


I think I'm doing it right.



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