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  #1  
Old 02-28-2019, 10:35 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 102
Default Vibration Problems

I have been having vibration problems with my RV-12. It ran smoothly at cruise, but when I reduced the power from about 4600 to 3000 there would be a vibration. I tried several possible solutions: 1, did the friction test on the gear box; 2, weighed the floats to see of they were too heavy; 3, sycnhed the carburetors; 4, replaced the soft engine isolators; and 5, replaced all the muffler springs. Since those didn't fix the problem I then decided it was the Gear Box. Ronnie and Morris Smith of South Mississippi Light Aircraft agreed with my thoughts.

Today I took the gear box to them for repair. The dogs were worn and the disks were worn. All were replaced and Ronnie says my vibrations will be gone. I will be out of town next week so I won't get the gear box back on to know for sure for a week or two. But if any one is interested, here are some pictures of the worn gears and dogs.

The aircraft has 450 hours on it. I ask Ronnie is this was from abuse, bad parts, etc. He said there was no way to tell. I have flown it 120 hours and I have not let it idle at slow speeds.

I am posting these pictures in the hope it will help others understand the problem if they experience vibrations like this.







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John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 140 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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  #2  
Old 03-01-2019, 12:08 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,321
Default

What was the condition of the magnetic gearbox inspection plug? Did it have excessive metal shavings on it?

I wonder if previous owner used incorrect oil not approved by Rotax for gearbox engine?
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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 421

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawks
and MJ Stricker (my flight instructor) - 1st Lt./Captain B-17H WWII

Last edited by Piper J3 : 03-01-2019 at 12:14 AM.
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  #3  
Old 03-01-2019, 08:38 AM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 102
Default Vibration

I have not seen anything other than some small fuz like particles on the magnetic plug, very small and very small quantity.

According to the logbook both previous owners used Aero Shell Sport Plus 4 oil.
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John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 140 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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  #4  
Old 03-01-2019, 09:05 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,115
Default

The primary things to focus on to minimize worn gear box parts is dynamic prop. balance, carbs that are well synced in the idle speed range, and avoiding operation below 1800 RPM (on some engines,staying at or above 2000 as much as possible seems to be a good idea).

Being casual about maintaining a proper carb. sync is a sure way to cause gear box wear.
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Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #5  
Old 03-01-2019, 10:36 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,321
Default

It's going to be interesting to see if wear on the cam angle surfaces indeed causes vibration in mid-range. I'm kind of thinking itís a stretch...
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Jim Stricker
Hinckley, Ohio (1OA2)
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 421

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawks
and MJ Stricker (my flight instructor) - 1st Lt./Captain B-17H WWII
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  #6  
Old 03-01-2019, 11:32 AM
dbhill916 dbhill916 is offline
 
Join Date: May 2013
Location: Westerville, OH
Posts: 139
Default cause vs effect?

Several decades ago, I was an engineer. Remnants of that life prompted my first thought to be "which came first, the vibration or the wear?" Like Piper J3, I think it's a stretch that the wear causes vibration. The converse seems more likely to me. Even if the wear did cause the vibration, what would have caused that wear in the first place? Scott's point makes me wonder about the first 330 hours you were not operating it.

On the other hand, results are results. Let us know what you feel when you get flying again.
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David B. Hill
N76012
RV-12 #0760
http://n76012.blogspot.com
Dues paid through 6-2019
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  #7  
Old 03-01-2019, 11:53 AM
romaja romaja is offline
 
Join Date: Jan 2016
Location: Vancouver, Washington
Posts: 27
Default Very similar scenario

Below is my post from several months ago. Magnetic plug clean. My carbs were always synced and dynamic balance was done from the start. No signs of gear wear. Once the gears were replaced the vibration was gone. Albeit, at a considerable expense.

Link:
http://www.vansairforce.com/communit...=912+vibration
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Jim Roman
Retired Airline
Rans S20 Raven Built 2016 (Repairman Certificate)
Vancouver, Washington
ATP, CFI, II, MEI
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  #8  
Old 03-01-2019, 01:04 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 8,115
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Understanding how component wear in the 912 gear box causes vibration requires an understanding of what wears and how the system works.
The damping system uses a spring preload of the 3 dogs on the gear pushing against the big gear and when ever the rotation relationship of the two parts (in the posted photos) exceeds the distance between them, the dogs begin to climb the ramp. What often wears is the base of the ramp so that it no longer has a gentle climb, but the slope of the one part slams into the slope of the other. By the time this wear has occurred, some of the other parts have worn and pre-load has changed so that even at some cruise power settings the damper can be reaching the ends of its travel and lightly crashing the ramps.
This produces a vibration that can be felt, but for someone not familiar, also hard to diagnose.
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Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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  #9  
Old 03-01-2019, 02:39 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 102
Default Vibration

Jim Roman,

When the gears and dogs were taken out, are you saying there was no sign of wear?
__________________
John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 140 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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  #10  
Old 03-01-2019, 04:11 PM
romaja romaja is offline
 
Join Date: Jan 2016
Location: Vancouver, Washington
Posts: 27
Default

Quote:
Originally Posted by pilotyoung View Post
Jim Roman,

When the gears and dogs were taken out, are you saying there was no sign of wear?
That is correct. The Rotax tech that took them out said no visible wear. Very similar to a gentleman in Alaska with a Rans S-7. Ronnie Smith has seen a few of these as well as Rocky Mountain Kitplanes. My engine was produced new in 2015 and so was another that had the same vibration problem. I have operated my engine as per Rotax operating instructions. I believe Rotax has fessed up to some gear vibration problems on the 912is but nothing yet on the 912ULS.

Jim
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Jim Roman
Retired Airline
Rans S20 Raven Built 2016 (Repairman Certificate)
Vancouver, Washington
ATP, CFI, II, MEI
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