Prop slipping on Rotax 582 w/ C gearbox?

22 posts in this topic

Posted

While running the Catalina a few times to tune the prop pitch in anticipation of engine break-in runs, I noticed that the prop is slipping slightly.  Never enough to notice it directly while running, but some index marks I made between the prop shaft and the PTO shaft seem to be creeping during any run that I applied momentary full power to check static RPM.   

 

I was fairly certain this wasn't acceptable, so I tore down the gearbox ($180 special puller, check) and reassembled the friction cone, adhering to the service bulletins on the topic (increased torque for the big nut, loctite adhesive compound on the cone surfaces, etc).  

 

It still slipped.   I tore down the gearbox again, this time taking every step I could to make sure surface prep, adhesive compound, and fastener torque was as good as I could make it.  I fully torqued the nut without the lock washer and with thread lubricant, to ensure the gear was as fully seated as it could be with those wrench settings, then cleaned the threads and replaced and torqued the nut with the specified loctite.  

 

It still creeps.  

 

I still assume this is not acceptable, but I thought I would verify.  Is the friction cone designed for some creep?  

 

Didn't think so.  Back to the workbench. 

 

J

 

 

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Posted

I believe at one time, Rotax's friction cone in the C box was a different taper than they went with later.  I was thinking the early one was 7.5 degrees, and the later one was 5 degrees to put more leverage on the gear to keep it from turning on the shaft.  When I looked in my LEAF catalog a while ago, I see that they only list the 7.5 taper part so I'm probably remembering things wrong on the 7.5 being the first one.  Maybe I read about this in the CPS catalog "Proper care and feeding of the Rotax engine" section.  At any rate, they changed the taper because of early problems with gears turning.   Any idea how old your unit is?  Do you know if it was ever taken apart before?  If a guy goes to the later taper, it requires changing the large gear also.  ($ OUCH!)  Try  to look in the CPS  catalog for the section on servicing the C gear box.  In answer to your question about is it designed to slip, I don't think so either.  Jim Chuk

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Posted

Thanks!  I'd read one earlier SI about retaining compound and higher toruqe, but had missed the later one about the new part.   I'm sure I have the old part- it's a 95 and the gearbox was probably never opened.   

 

Here's the SI discussing the part changes:  http://www.rotax-aircraft-engines.com/portaldata/5/dokus/d04298.pdf

 

The new gear and gone does indeed add up to about $600.  Ouch indeed.  

 

The later SI advises a higher ever torque setting and normal flat washer for all previous part numbers, so I'll try one more time with the extra kick.  I might warm the gear to about 300 degF in an oven- by my back of the envelope calculations, that would fit tighter by about as much as an extra 1/5th turn of the nut, but without the stresses on the nut/cone/threads that overtorquing it would impart.

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Posted

Just looked in my Rotax repair manual, and it says that the change to 1 in 7.5 taper was made in 1991.  I guess my memory was a bit off on some things.  I was thinking the taper was measured in degrees, that was why I thought the change was to a smaller degree.  Instead it was measured in taper ratio.  In that case, 1 in 7.5 is less taper than 1 in 5.  If you want, I can copy the 2 pages in my manual that deal with this and send them to you.  At any rate, it doesn't appear that you have the older gear box.  Jim Chuk

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Posted

I'd love to see the documents that you have.  It looks like after the change in '91 to a 7.5:1 cone, they issued a SI in '06 suggesting adhesive compound and a higher torque, then changed the part again in 2008 to a 1:10 taper (so an even shallower cone) and upped the nut torque even more for all part numbers. 

 

While I had it apart, I identified the cone as described in the '08 SI, and it's indeed the 7.5 cone, which coincides pretty well with the date of the unit. 

 

So I cleaned everything perfectly, took a stone and applied a pretty axial hone pattern on all the friction surfaces, used AC648, and warmed the gear to 350degF in the oven before pressing it on.  I set the nut with thread lube, a greased flat washer and a very liberal interpretation of 220ft-lbs of torque, then removed it, cleaned the threads, and did final assembly it with loctite, the serrated washer, and the proper torque. 

 

In short, I did about everything I can think of to help the existing part work.  If it slips again, the way I see it, I've got no choice to buy new parts.  And then I might as well upgrade to an E gearbox and a slipper clutch :)  Sigh. 

 

J

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Posted

Here are the two pages from my manual that deal with the friction cone and the large gear.   The info is at the bottom of the pages. Jim Chuk

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post-329-0-65781300-1398306284_thumb.jpg

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Posted

You can't use the clutch with the e gear box. I don't have any other answers for you. I used sleeve retainer on mine when I put it back together and so far no slipping.

:BC:

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Posted

What prop are you using?  The thumbnail looks like a three blade of some type.  I'm wondering if it has a high moment of inertia, making your situation difficult.

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Posted

That's a Warp Drive 70".  I don't know how it compares to other props, but that's an idea worth looking at.  

 

J

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Posted

Taper tip, or square?  The square tips are known to have a pretty high moment, especially if they have the metal leading edge.  I believe that's why the taper tips exist.

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Posted

A 912 gearbox max weight is a 3-blade 68" warp with nickel leading edge and tapered tips. Any more and the max moi is exceeded.

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Posted

A 912 gearbox max weight is a 3-blade 68" warp with nickel leading edge and tapered tips. Any more and the max moi is exceeded.

That sucks if you want to use a longer prop.  You would think they would build it to take a very popular standard 70" to 72" prop.  Just another reason why Rotax anoys me.  Like the $600 gear to take care of the SI.  After paying the extorsion prices Rotax charges for their engines you would think that when they discover a screwup on their design they would offer the parts to rotax owners at or near cost instead of continuing to rob them.

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Posted

I understand that the IVO prop is a lot lighter than the WD.

EdMO

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Posted

That sucks if you want to use a longer prop.  You would think they would build it to take a very popular standard 70" to 72" prop.  Just another reason why Rotax anoys me.  Like the $600 gear to take care of the SI.  After paying the extorsion prices Rotax charges for their engines you would think that when they discover a screwup on their design they would offer the parts to rotax owners at or near cost instead of continuing to rob them.

 

 

Yet still, the Rotax 912 series are the best engine available for a light sport class airplane...

 

Weight, power and RELIABILITY.

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Posted

^ sez the guy with the new gearbox!

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Posted

oh snap! 

:snack:  

 

:BC:

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Posted (edited)

Says the guy whose gone to funerals of Subaru pilots. My minor gearbox issue, stemming from a too heavy prop, didn't KILL me. Don't even try going there.

I've derailed this thread too much already, sorry cowlove. I'll go away now.

Edited by Av8r3400

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Posted

Do go away just yet. Where do I find info on sube ea81 failures. I'm flying one with no problems but I'd like to know potential problems. Thanks.

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Posted (edited)

I have heard only 2 reports of EA-81 failures - but there may have been others.  In both cases it was ignition failure because of poor maintenance.

I would say that the EA-81 has a better record than some other engines.

EDMO

A friend of mine wrecked his new RV with an Soob-2.5, but it was not the fault of the engine - he had put an untried, untested, experimental, Eggenfeldner Supercharger on the engine and it failed.

Edited by Ed In Missouri

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Posted

Well, my the last assembly attempt held through two quick full throttle bursts.  I'll have the entire engine break-in period and some pretty extensive water trials to convince myself that it's solid. 

 

It's the warp drive 3 blade, square tip, with nickle leading edges.   After the plane is flying, I'm going to assess how it gets off the water.  I'm definitely not near that point yet, so hesitate to spend to much time thinking about it,  but two tricks I might consider would be one of the adjustable propeller hubs and a Rotax Rick 670 conversion.   If I do end up shopping new props, moment and weight will definitely be a prime factor!

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Posted

What diameter is it?

 

Warp props are very heavy duty and well built props, but, especially the square tip ones, are extremely heavy.  With the nickel leading edge this puts them over the max for the Moment of Inertia test that Paul was referring to.

 

MOI Test Procedure

 

The "B" gearbox can only tolerate 3000 kgcm2.

 

The "C" & "E" gearboxes can tolerate 6000 kgcm2.

 

The 912/914 gearboxes can also only tolerate 6000 kgcm2.  (Link)

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Posted

Boo.   Measured the rotational inertia at about 6300kgcm^2.   Well, that pushes me towards the adjustable pitch propeller sooner rather than later.  Sad that I probably won't be able to re-use the WarpDrive blades with a FP hub.

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