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  #1  
Old 04-01-2019, 07:58 AM
Cammie Patch Cammie Patch is offline
 
Join Date: Oct 2018
Location: Boise, ID
Posts: 18
Default Gearbox wear: Mobile 1 vs Aeroshell

I have an RV12 SLSA with 300+ hours on it. It has run Aeroshell Sport 4 since birth. I bought it at about 165 hours, and it has had quite a bit of vibration at low RPMs. At startup, I have to idle close to 2500 RPM to keep the vibration under control. I've rebuilt the carbs, and balanced them a few times. I've noticed quite a bit of ferrous metal on the magnetic plug and in the filter. I believe that the dog gears have excessive wear, which is very annoying since it has been run according to specs.

I also have an AutoGyro Calidus with a 914 motor. It has over 800 hours. Magnetic plug and filter are always very clean. It idles very smooth. It has used Mobile 1 4T since birth.

I'm wondering if the oil has something to do with the wear. I am curious what oil others have been using, and if they have seen metal in the filter/magnetic plug. I suspect that Mobile 1 has better gearbox additives.

Both engines are almost completely run on 91 octane non-ethanol fuel, although the RV12's fuel before I bought it did have ethanol.

What has been your experience?

Cammie Patch
Glass Cockpit Aviation
A&P/IA/LSRM/CFI
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  #2  
Old 04-01-2019, 10:04 AM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 150
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If you have noticed a lot of metal on the magnetic plug and you have vibration problems I would identify their source before this causes premature wear in other parts of the engine. If you suspect the gearbox then I would have that properly serviced by rotax center and I would ask them advice on what else to properly inspect on the engine.
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  #3  
Old 04-01-2019, 10:07 AM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 133
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You are asking a lot of people here that believe Aeroshell is the only acceptable oil for use in a Rotax 912ULS with gearbox.

Some people have gearbox failure at low hours. I am not an engineer, nor a lubrication specialist or tribologist, but something is telling me there is lubrication failure in the gearbox, that you start getting metal to metal wear, with no protective oil barrier between the two parts that are wearing.

I'd say, pull your gear box, get it rebuilt and fixed up right, and then run the Mobil 1 4T oil with MOgas only in your 912ULS in the RV-12, and change your oil and filter every 50 hours, as you would with Aeroshell.

Get back to us when another 300 hours are on the motor and gear box in the RV-12, and do a gearbox inspection. If your gearbox is still good, you are but one statistical point that shows what the difference in brands of oil makes on this motor and gearbox. You get to be a guinea pig. You also have the ability to enlighten us as to if the boundary layer lubrication properties are better with Mobil 1 T4 than AeroShell Semi Synthetic.

If you run LL100, your oil options are a lot less, not many will handle all the lead in the fuel. Rotax designed the motor to run on unleaded fuel.

The other theory is that Rotax has a bunch of gearboxes in 912 ULS motors that have soft steel parts, or inadequately hardened steel parts in the gearbox, that won't handle the increased compression going from an 80 HP UL to the 100 HP ULS design, and that is causing the failure mode.

Take your pick, as to cause of failure.

Last edited by NinerBikes : 04-01-2019 at 10:16 AM.
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  #4  
Old 04-01-2019, 11:24 AM
Cammie Patch Cammie Patch is offline
 
Join Date: Oct 2018
Location: Boise, ID
Posts: 18
Default

Just for background, I am an A&P/IA Rotax tech, Rotax heavy maintenance qualified, and have been working on Rotax 4 cylinder aircraft engine for about ten years. I've worked on gearboxes quite a bit. I've ordered new dog gears, as I want to have them on hand when I open it up so I have a quick turnaround.

Rotax markets the AeroShell because of the relationship between the two companies. The recent reformulation of the AS made it a better (than it was) oil, but I actually believe that the Mobile 1 has better gearbox additives.

My plan is to run the mobile 1 exclusively once I get the gearbox opened and cleaned.

But, I'm asking for feedback from those who have had the gearbox wear.... What oil were you using? Has anyone had the wear when using the mobile 1?
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  #5  
Old 04-01-2019, 03:32 PM
Dave12 Dave12 is offline
 
Join Date: Oct 2010
Location: Elkton, Md.
Posts: 1,409
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Hi Cammie, I have been chasing a vibration in my 12 for quite awhile. This vibration I experienced was throughout the rpm range and increased with engine speed. Starting with the usual culprits, I checked the carb synch, found them out of synch and fixed that. It did seem better of course, but they soon fell out of synch again and again. At this point I replaced the throttle cable and cured that. I then replaced the engine mounts which netted no difference. I then balanced the prop. It did feel better, but still not smooth. I worked on the balance a bit more and got the final results to .02 ips at 4900 rpm. It actually shows .00 ips in some rpm ranges, so that ruled out the prop. I will say that all along I have suspected the gearbox, but with 400 hours I felt it was a bit premature, but entirely possible. A couple weeks ago, as my wife walked away, I started the engine and she told me later that “something didn’t sound normal “. At this point I was pretty confident in my suspicions of the gearbox. I immediately pulled it and sent to Lockwood’s. As it turned out, the ball bearing in the front of the gear box on the prop shaft was noisy. I’ve never found any metal and have always used Aero shell. It’s smooth now.
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  #6  
Old 04-01-2019, 04:24 PM
Cammie Patch Cammie Patch is offline
 
Join Date: Oct 2018
Location: Boise, ID
Posts: 18
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That's interesting . I haven't seen a problem with that bearing unless there was a prop strike. When that happens, it can bend the bolts that hold the bearing in place, and you may find cracks radiating from the bolt holes.

When doing a prop balance, you can determine if it's the engine or the prop that's causing the IPS by looking at the frequency. If it's at the engine RPM, it's the engine. If it's more like the engine RPM divided by 2.43 (the gearbox ratio), then it's a prop imbalance. These light props are more forgiving of inbalance, but it will still help to balance them.

Quote:
Originally Posted by Dave12 View Post
Hi Cammie, I have been chasing a vibration in my 12 for quite awhile. This vibration I experienced was throughout the rpm range and increased with engine speed. Starting with the usual culprits, I checked the carb synch, found them out of synch and fixed that. It did seem better of course, but they soon fell out of synch again and again. At this point I replaced the throttle cable and cured that. I then replaced the engine mounts which netted no difference. I then balanced the prop. It did feel better, but still not smooth. I worked on the balance a bit more and got the final results to .02 ips at 4900 rpm. It actually shows .00 ips in some rpm ranges, so that ruled out the prop. I will say that all along I have suspected the gearbox, but with 400 hours I felt it was a bit premature, but entirely possible. A couple weeks ago, as my wife walked away, I started the engine and she told me later that “something didn’t sound normal “. At this point I was pretty confident in my suspicions of the gearbox. I immediately pulled it and sent to Lockwood’s. As it turned out, the ball bearing in the front of the gear box on the prop shaft was noisy. I’ve never found any metal and have always used Aero shell. It’s smooth now.
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  #7  
Old 04-01-2019, 05:13 PM
Dave12 Dave12 is offline
 
Join Date: Oct 2010
Location: Elkton, Md.
Posts: 1,409
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I have balanced a few Sensenich props on the 912 and found that it usually doesn’t take much weight at all to bring them way down. My prop is the exception. It took a little more than usual to tame it. I am thinking that could cause premature failure of that front bearing. I think I first balanced it around 275 hours as soon as I felt the vibration. IMO, all of these props should be balanced. There is absolutely nothing to lose. I’m taking appointments.

Btw, Joe at Lockwood’s was surprised to find this bearing in a failed state. They have replaced very few of them.
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  #8  
Old 04-01-2019, 05:47 PM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 133
Default Mobil 1 T4 10w-40

For future reference, this is the Synthetic Mobil 1 Motorcycle oil with gearbox additive the OP is referring to. Mobil 1 Full Synthetic 4T 10w-40.

https://www.walmart.com/ip/Mobil-1-1...-1-qt/16767829


Another item brought up often is frequently verifying that your Carburetors are synchronized.

Last edited by NinerBikes : 04-01-2019 at 07:48 PM.
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  #9  
Old 04-01-2019, 10:42 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,441
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Cammie,

How confident are you that there wasn’t anything like a prop strike before you acquired the plane? That might explain things.

Rich
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  #10  
Old 04-02-2019, 09:05 AM
Cammie Patch Cammie Patch is offline
 
Join Date: Oct 2018
Location: Boise, ID
Posts: 18
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Very. Original prop serial number.
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