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Slyfox
02-14-2011, 09:51 AM
I have a little concern about the 912uls gear box. Yes I do have the 912uls. But, on the VAF I read this morning that an RV12 went down apparently because of a possible engine out and that it might have blown the gear box, in that measage another person came out with the fact that his rv12 went quiet as well with the gear box as a possible problem. I know there was a kitfox a few months ago that had to force land and it had a possible gear box failure.

Now I know there was a series of 912uls motors about 3 years ago that had issues with the gear boxes and there was a bulletin about this. Is this just isolated to this problem and nobody checked the serial no. on there engines before flying them or do we have a problem with gear boxes that are just now showing up. I'm talking engines that are around 3 years old here.

szicree
02-14-2011, 10:15 AM
I read that post as well and share your concern. The pilot said that he suspected a siezed gearbox. I'm hoping that he'll tear into it real soon and share his findings. Until then it's really just guessing.

DesertFox6
02-16-2011, 08:22 PM
Something sounds eerily familiar about this thread; I personally know of two late-model 912S equipped Kitfoxes that had what were initially thought to be carburation problems but were later, correctly, diagnosed by our favorite local "Desert Fox Squadron" affiliate-engine-guru as gearbox problems. He quickly fixed both, citing improper factory shimming in both cases if my memory serves. He said this can easily lead to extra "slack" in the geartrain, which gets worse with time, and, eventually, bad stuff can happen.

I'll let the pilots involved describe their particular situations and symptoms if they happen to read this and want to add on, but any apparent 912 (late model, certified or "un") engine vibrations or harmonics that might be suspected "carburation problems" that won't go away despite all logical adjustments, to include carb replacement (!) might very well be gearbox problems. It's insidious!

This is just too serious to pass by, so if we don't hear from anyone with any additional info on this thread in a day or so, I'll contact both pilots and ask them for their inputs. Neither engine suffered a failure, they're dang near bullet-proof, but some pretty serious stuff was going on in flight!

"E.T."

Slyfox
02-17-2011, 09:18 AM
DessertFox6,
this is interesting stuff. I do know that you should have some end play in the gear box. To check just grab the prop and move it left and right with little movements, you should feel a freeplay . If looking at the center hub you should have about 1/8 end play. beyond 1/4 and I would be looking inside the gear box for worn out spacers and such. I've done two rebuilds on the gear box on my old 80hrs rotax and it is very easy to check and do yourself. Are you saying that the ones with problems had too tight a gear box or too loose?

Another thing we owners should be doing is removing the bolt on the side of the gear box, there is one that is wired in place and it has a magnet to collect material. Of course if there is material, a problem is possible. Rotax says when we do an oil change to check this.

DesertFox6
02-17-2011, 07:54 PM
As I recall, both instances of gearbox vibration were due to "looseness;" one was on a 912ULS while the latest one was on a certified engine...not that there's any difference in the way they're assembled or tested: That "difference" is really just in paperwork. Our local Rotax guru said both were a factory-caused issues; they came that way right out of the box and only time/wear was necessary for each problem to manifest.

I attended Erik Tucker's excellent engine tear-down course a number of years ago at CPS in San Leandro for my 80 horse and he covered exactly the points you mentioned but no such gearbox issue had shown up at that time. I've not heard of any such shimming problems with the UL engines, just the two ULS instances I mentioned before. I'll contact both pilots tomorrow.

These are, admittedly, VERY rare instances and well less than any "negatives" I've heard associated with ANY other engine, but the RV12 incident was news to me. Today I spoke to a friend with a Jabiru (what a horror story!) in his RANS who was REALLY interested in what my Rotax experience has been: I think I converted him in less than two minutes, so, big-picture-wise, we're still the luckiest experimental pilots in the world.

As they say on TV..."Film at eleven..."

"E.T."

DesertFox4
02-17-2011, 10:28 PM
I had one of the gearbox issues DF-6 mentioned. When my 912uls had about 400 hours it started to have starting issues. Hard starts would be the way to describe it. It would fire quickly but shake pretty hard before clearing when I advanced the rpms. Sometimes even spilling fuel out the overflow tubes.
Ok, must be a carb issue as they are the weak link on the 912's. Sync. carbs. Not much improvement but operable. Check for vacuum leaks, new carb boots, cross-over tube OK. Carbs. set correctly. New plugs, ect.
Over a months time or so I saw a slow degradation in the smoothness at start up. Seemed to be worse when it was cooler out.

Jump ahead. The Desert Fox Squadron now finds itself in Idaho on a summer trip. Cool morning and I start the Rotax. It's very violent. Can't get the engine to spool up very well to get out of the shaking, low rpm gearbox chattering range. Something isn't right. We change plugs again and all the usual things are checked. I'm able to fly it back to Arizona OK but am not happy with this situation. Must be a carb issue so I go through both carbs. Find nothing wrong. Still won't start decent. Tired of a month of fighting this. Call Steve Beatty at Airscrew Performance. Give him the facts and he diagnosis it over the phone as a gearbox problem. I'm stunned. :confused: What does that have to do with my 912S starting crappy. He explains that the gearbox has gone "out of spec" and needs to be re-shimmed. The impulses from the engine are fighting the inertia of the prop. mass and they are trying to cancel each other out. (I hope I'm explaining this correctly as this is how I envisioned it when he described it over the phone.)


I remove the gearbox and deliver it over to Steve's shop. After a couple days he says it's ready to pick it up. Install gearbox and attach prop.


Start up is instantaneous and smoooooth. Just like a new engine. No gas puking out the overflow's and no shaking. I'm back baby!!!!!:D
I now have 365 hours on it since the gearbox was adjusted and it still works perfectly. Thanks Steve!!
BTW- while my gearbox was at Steve's I had him install a clutch in it. It was supposed to have one in it but as it turned out it did not. I think when I get another 200 hours on it I will take it off and let Steve go through it again. It's cheap insurance for the piece of mind.

Had a friend here in Phoenix go through the same symptoms and we decided to take his gearbox to Steve and got the same happy results on that 912S also.

I've since modified my start and shutdown procedures and of course installed the slipper clutch so I've done all the proper things to help reduce gearbox premature wear except install a "soft start system" and have my prop. balanced with a Dynavibe balancing system. DynaVibe prop. balancer info: (http://www.rpxtech.com/rpxweb/Dynavibe.asp) (shameless plug for one of our fine sponsors.);)

That would be a good next step to getting max life from my gearbox.

Slyfox
02-18-2011, 09:04 AM
Desertfox4,

That is very interesting. I to have troubles starting my fox, it's like it's got a compression lock or something. What I do is pull the throttle all the way off, my idle is set for 500rpm. I let it kick and when it turns smooth I put on a little throttle and starts right up nice and smooth and quick. I don't know if I have a gear box problem but this has been since new. I have no other problems. Is there any way of checking for a bad setup on the gear box. I know of the end play that should be in the gear box by moving the prop back and forth and mine seems to be ok. Maybe a number for steve would be helpful and I can call him and talk. thanks

Dorsal
02-18-2011, 09:40 AM
It is my understanding that this is part of the reason that the "soft start" is included with all new 912 engines. It was explained to me that after the above symptoms the next thing to go would be the sprag clutch adding to the experience of rough starting. I installed the after market soft start module (took about an hour) and it appears to work well. Naturally I can't know if it will have prevented the issues but it makes me feel good :)

Slyfox
02-18-2011, 09:49 AM
soft start, what is that?

I concider my way of starting, soft start, it really is nice.

DesertFox6
02-18-2011, 12:20 PM
Thanks for sharing your "wild ride" story with everyone, DesertFox4; you were one vexed puppy through that ordeal and none of us could offer a helpful clue until you got Steve Beatty involved. He's quite a guy; not much for BS or chit-chat, but a mechanically-minded, walking encyclopedia of engine-savvy skills.

For the rest of the team out there, you can contact Steve Beatty's Airscrew Performance LLC shop in the Glendale, Arizona neck'a'the woods at (623) 842-3902. Tell him his local Kitfox buds sent you... :)

"E.T."

Dorsal
02-18-2011, 01:10 PM
soft start, what is that?

I concider my way of starting, soft start, it really is nice.

The soft start module retards the spark during starting, apparently good for the higher compression of the 912S.

chefwarthog
02-18-2011, 02:14 PM
He guys, excuse my ignorance but what is a "soft start system" and ''the slipper clutchand'', how it works?, do we have to buy the system separate?, does any body have picture of it for me, just to go to bed tonight less ignorant....:o

Eric

Dorsal
02-18-2011, 03:03 PM
You can learn more about the BullyHawk soft start module on the Rotax Owners site www.rotax-owner.com, the slipper clutch I believe is pretty much standard with 912S engines at this point.

chefwarthog
02-18-2011, 03:09 PM
You can learn more about the BullyHawk soft start module on the Rotax Owners site www.rotax-owner.com (http://www.rotax-owner.com), the slipper clutch I believe is pretty much standard with 912S engines at this point.
'' Merci '' Dorsal, i will go see that right now

thanks

Eric

mcomeaux53
09-09-2014, 09:01 PM
I HAVE a 912ULS that has this strange vibration that occurs after approx. 1 hour of flight at cruise setting 5K. After pulling off power a bit it translates a bit more to a concern level:eek:. I continue to pull power back to 28-32k then back to cruise power and it smooths out for a bit. I've done all the most obvious carb rebuild/sync/plugs compression etc. This is a used aircraft to me that is a 2004 with 312 hours and very little maintenance. I'm going after the gear box next and will post my findings. Anyone else want to chime in feel free to and any advice would be much appreciated.

Regards

Mike

Floog
09-10-2014, 06:33 AM
RE: "I've since modified my start and shutdown procedures." Can you elaborate on your 'procedures', DF4. I have soft start. 912 always starts easy, but abrupt stop at shutdown is a concern. Thanks, Floog

68niou1
09-10-2014, 07:11 AM
I HAVE a 912ULS that has this strange vibration that occurs after approx. 1 hour of flight at cruise setting 5K. After pulling off power a bit it translates a bit more to a concern level:eek:. I continue to pull power back to 28-32k then back to cruise power and it smooths out for a bit. I've done all the most obvious carb rebuild/sync/plugs compression etc. This is a used aircraft to me that is a 2004 with 312 hours and very little maintenance. I'm going after the gear box next and will post my findings. Anyone else want to chime in feel free to and any advice would be much appreciated.

Regards

Mike

Mike- if it is smooth for a full hour and then starts to act up I would look real hard at your fuel system (tanks, filters, fuel lines, fuel pump) depending on the year there have been many cases of debris, or something stupid like a fuel line collapsing on itself due to age. Normally when the gearbox is bad it's bad from from the get go(rough idle, vibration at different rpms) at least in my limited experience;) Good luck- Scott

mcomeaux53
09-10-2014, 09:34 AM
I forgot to mention the new fuel lines and filters......been there done that to...

jiott
09-10-2014, 10:41 AM
Floog, regarding abrupt shutdown: The procedure I use (read it somewhere) is to reduce engine speed to idle (mine is set at 1650), then switch off ignition A and wait for a couple seconds, then switch off B and wait a couple more seconds, then both off. This brings the idle speed down to about 1400 rpm so the shutoff is not as abrupt.