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Wheel Bearings.

rv8or

Well Known Member
Since I posted on another thread on bearings, I thought the following would be helpful for wheel bearing life.

In use the wheel breaths and this can affect bearing life particularly if parked for a couple of weeks or more.
So how does the wheel breathe, it breathes due changes in temperature. When applying the brakes the hub heats up, the air inside the hub expands and breathes out through the seal and when it cools down it breathes in.
The air coming in brings in a certain amount of moisture and this moisture will condense on the inner walls of the wheel.
When the wheel is heated up again it is not hot enough to vaporise all of the water and on cooling more water is added until over a few cycles small droplets form and it is these droplets when they get into the bearing which will form small rust lines if left sitting. Commonly visible as dark staining at roller spacing. This rust etching forms a stress point which dramatically lowers the fatigue life and is most common with a rough running bearing.

There are a couple of simple actions that can reduce the build up of water droplets on the inner walls of the wheels.

1. Fly lots then the water does not have sufficient time to etch the bearing tracks before it is wiped away by the bearing rollers turning. (Best solution)

2. By applying a thin layer of grease to all of the exposed inner surfaces of the wheel this will reduce water droplets forming on the surface keeping the moisture suspended in the air.

Hope this helps
Rob
 
3. Move out to the southwest where you can fly year round and moisture isn’t an issue.
 
3. Move out to the southwest where you can fly year round and moisture isn’t an issue.

I live on the Oregon Coast and moisture in my wheels and bearings, or any part of my airplane isn’t an issue. I fly year round, just not as much in winter as one can imagine. Not moving to dry country just to fly more in the winter but to each their own.

I appreciate the OP’s comments, but I just inspected and packed my wheel bearings, like I have for the last 16 years on the RV and for my much longer entire aircraft ownership life. I don’t believe properly greased and maintained bearings will ever have a problem. Again, I am in a wet environment. Also never had any issues with my boat trailer which gets “dunked” in salt water all the time.

Keep ‘em properly greased or move to the SW and get sand and dust in your shorts, and everywhere else, including your bearings if you don’t maintain them.
No cut on the SW, love to visit.
 
I live on the Oregon Coast and moisture in my wheels and bearings, or any part of my airplane isn’t an issue. I fly year round, just not as much in winter as one can imagine. Not moving to dry country just to fly more in the winter but to each their own.

I appreciate the OP’s comments, but I just inspected and packed my wheel bearings, like I have for the last 16 years on the RV and for my much longer entire aircraft ownership life. I don’t believe properly greased and maintained bearings will ever have a problem. Again, I am in a wet environment. Also never had any issues with my boat trailer which gets “dunked” in salt water all the time.

Keep ‘em properly greased or move to the SW and get sand and dust in your shorts, and everywhere else, including your bearings if you don’t maintain them.
No cut on the SW, love to visit.

Ha Ha……. Good one. Bottom line, fly your airplane frequently, no matter where you live. If you don’t, you will need do do more in terms of maintenance and inspections. It’s always been that way.
 
For the past 44 years all I have used is this on my wheel bearings
and have never had to replace a bearing, or found any moisture....
grease WB.JPG

You may have an issue with your bearings breathing in
moisture if you don't service them (if hangared) every
few years... maybe when you do the brakes.
 
Commonly visible as dark staining at roller spacing. This rust etching forms a stress point which dramatically lowers the fatigue life and is most common with a rough running bearing.

Do you have a picture of what this looks like?
 
Wheel Bearings

The advice on bearings I wrote in the start of this thread is of course only advice but as a trained professional bearing engineer this is what I would advise.

In one’s professional life as an engineer there are few really top notch experts or to put it another way a guru in their field and I was lucky enough to be trained by a guru in the field of bearings. Ruben John Smith (John Smith) was 6’4” ex Catalina navigator during the war flying in sea cats either on missions to drop mines/depth on the Japanese or searching for downed pilots and aircrew, some of his missions were as he put it mildly character building. An absolute gentleman engineer of the old school.

So this advice is not knew John passed this advice to me from hard won experience and in 50 years (took early retirement at 70) of working as a professional engineer I have been very grateful of the lessons he took his time to teach me. Also note for clarity I have not worked as a bearing engineer all my working life but the lessons are still there.

As some have pointed out regular maintenance and usage negates problems and as I said my note is only advice so whatever works for you.

What prompted me to write the note you will see in the attached photo is a bearing removed from an RV at an airfield near to me. I had to retrieve the old one from the owner so I could attach a photo of it.

Rob

Etch Failure.jpg
 
The advice on bearings I wrote in the start of this thread is of course only advice but as a trained professional bearing engineer this is what I would advise.

In one’s professional life as an engineer there are few really top notch experts or to put it another way a guru in their field and I was lucky enough to be trained by a guru in the field of bearings. Ruben John Smith (John Smith) was 6’4” ex Catalina navigator during the war flying in sea cats either on missions to drop mines/depth on the Japanese or searching for downed pilots and aircrew, some of his missions were as he put it mildly character building. An absolute gentleman engineer of the old school.

So this advice is not knew John passed this advice to me from hard won experience and in 50 years (took early retirement at 70) of working as a professional engineer I have been very grateful of the lessons he took his time to teach me. Also note for clarity I have not worked as a bearing engineer all my working life but the lessons are still there.

As some have pointed out regular maintenance and usage negates problems and as I said my note is only advice so whatever works for you.

What prompted me to write the note you will see in the attached photo is a bearing removed from an RV at an airfield near to me. I had to retrieve the old one from the owner so I could attach a photo of it.

Rob

View attachment 36288

I would argue that problems like this are often related improper maintenance procedures or using the wrong grease. Back before integrated wheel bearing in cars, we had a LOT of exposure to traditional, grease packed taper roller bearings. Corrosion, as shown in your pic, was not that common. Bearings were only serviced at brake changes (rarely less than 2 year intervals) and if packed properly rarely saw this kind of corrosion. Inactivity can cause issues with oilled bearings, but greased bearings, when properly serviced, do not typically see this kind of corrosion from inactivity. I am not a bearing engineer, but have seen my share of front wheel bearings on cars. I suspect that many amateurs do not understand that grease is not all the same. You generally need a grease rated for disc brakes in applications like ours that need a higher temp rating, otherwise the grease gets very thin when the rotors get hot.

This kind of problem is seen in trailer bearings, but they get their entire cavities filled with water that cannot easilly be expelled.

I look at that bearing and my first guess is that it was not properly packed with grease. Some probably just smeared grease on the outside of the bearing, without packing grease behind the cage.
 
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2. By applying a thin layer of grease to all of the exposed inner surfaces of the wheel this will reduce water droplets forming on the surface keeping the moisture suspended in the air.
I'm going to question this one. Moisture condensing from the air is mostly due to the temperature change, and not the surface material. So whether the surface is metal or a thin layer of grease over metal, doesn't matter.

What the moisture does once it's condensed on the grease vs. what it does when condensed on the metal will be different, I agree. But that just comes down to making sure you have adequately greased your bearings, and that you're using them and distributing that grease over the surface.
 
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