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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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 Posted: Wed Feb 03, 2010 5:44 am Post subject: Gearbox shimming |
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I just completed my Rotax 912 refresher course and I believe I have found the source of my occasional kickback/dieseling on shutdown that I have mentioned on this forum several times. This may not be a good description but essentially sometimes when shutting the engine down the prop would turn backwards 3 or 4 revolutions. Now, on occasion, during cold start, the engine will hang at around 1200 rpm and no amount of throttle will pull it out of that rpm. The engine just shakes and it screws up the carb fuel flow(ie: float and needle bouncing up and down) . I have to turn off the ignition and do it again
The instructor seems to think these two problems indicate weak Bellevue (sp) washers in the gearbox. My engine is older than most of yours, I suspect(1993)It only has 230 hours but over time these springs have weakened and it is shim time.( as well as overhaul time if my plane was not experimental) The theory is the weakened springs have allowed the "dogs' to separate at shutdown and to flip the prop backwards on the backside of the "hill" of the dog,so to speak. It is difficult to explain without the parts in front of you. I am thinking about installing the slipper clutch also as my engine does not have one.
Soooo now I have to make a tool to remove the gearbox.
Dick Maddux
912UL
Milton,Fl
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Wed Feb 03, 2010 7:12 am Post subject: Re: Gearbox shimming |
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Hi Dick,
Which course did you attend? Was it in Sebring?
ijr
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Ira N224XS |
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Wed Feb 03, 2010 7:22 pm Post subject: Re: Gearbox shimming |
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Hi Dick,
Your friction torque test should tell you if they are weak.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Thu Feb 04, 2010 5:11 am Post subject: Gearbox shimming |
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Roger,
I have the old 80 hp with just the "dogs'. I don't have a friction torque test as far as I know. There is no space between the "valley " of the dogs (sounds like a movie) just two "V" ,s put together so no friction to check. I believe that's on the 100 hp model.
Dick Maddux
912UL
Milton,Fl
[quote][b]
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Thu Feb 04, 2010 5:38 am Post subject: Gearbox shimming |
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Ira,
I attended the course at South Miss Light Aircraft with Ronnie Smith.( two hour drive) Two years ago I attended Dean Vogels (at) Lockwood. (superb !!) This was a refresher course for me as I have much to do on my engine. I attended the two day Service course which was an excellent fast paced review of systems, oil changing,purging,carb syncing,etc. These courses add up to a bit of cash so I did not take the Line Maint course again. I don't do this for a living but want to stay "up to speed" on this engine.
Case in point, as many of you know, was my little piece on the Kiev prop. I love it but could not get the necessary 5200 min static rpm out of it (per the new Rotax service bulletin/instruction) and still have the cruise I have with my Warp. Even though this prop is far smoother, easier on the gearbox and nicer looking, it would not work on my 80 hp Rotax on my Kitfox.
Ronnie showed us a Rotax case with a crack in it which was a result of an "overboost" .Rotax has since strengthen the cases. (after 2007 I believe)
I took copious notes during the course, as a lot of tips were being passed around.
I also attended the two day two stroke course as I was curious about that engine as we have one guy on our field who has one in a Challenger.(503)
Dick Maddux
912 UL
Milton,Fl
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Thu Feb 04, 2010 5:49 am Post subject: Gearbox shimming |
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There's no turbo so what is meant by "overboost"? Just curious.
Rick Girard
On Thu, Feb 4, 2010 at 7:37 AM, <Catz631(at)aol.com (Catz631(at)aol.com)> wrote:
[quote] Ira,
I attended the course at South Miss Light Aircraft with Ronnie Smith.( two hour drive) Two years ago I attended Dean Vogels (at) Lockwood. (superb !!) This was a refresher course for me as I have much to do on my engine. I attended the two day Service course which was an excellent fast paced review of systems, oil changing,purging,carb syncing,etc. These courses add up to a bit of cash so I did not take the Line Maint course again. I don't do this for a living but want to stay "up to speed" on this engine.
Case in point, as many of you know, was my little piece on the Kiev prop. I love it but could not get the necessary 5200 min static rpm out of it (per the new Rotax service bulletin/instruction) and still have the cruise I have with my Warp. Even though this prop is far smoother, easier on the gearbox and nicer looking, it would not work on my 80 hp Rotax on my Kitfox.
Ronnie showed us a Rotax case with a crack in it which was a result of an "overboost" .Rotax has since strengthen the cases. (after 2007 I believe)
I took copious notes during the course, as a lot of tips were being passed around.
I also attended the two day two stroke course as I was curious about that engine as we have one guy on our field who has one in a Challenger.(503)
Dick Maddux
912 UL
Milton,Fl
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[b]
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Fri Feb 05, 2010 5:10 am Post subject: Gearbox shimming |
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> There's no turbo so what is meant by "overboost"? Just curious.<
Rick, sorry about that,what I was referring to was the prop/rpm not in the correct range. I should have said too far over square. If you get too much pitch you can overtax the engine with too much stress. Like trying to turn a flat board against the air. The damage to the Rotax engine occurs in the case apparently.
Rotax specifies a min of 5200 static rpm with a fixed pitch prop.
Dick Maddux
Milton,Fl
[quote][b]
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