Technical Wheel bearing blues!

If the military aircraft that set longer than a month were required to be moved to prevent wheel bearing damage...Setting forces the rollers thru the film of grease and causes flat spots in the race and rollers....Not rust....Whatever it was called it wasn't good for wheel bearings...

 

False brinneling p 36 here -
https://www.farrellbearings.co.nz/site/farrellbearings/files//FAG bearing Damage.pdf

It is related to fretting/rust.

 

@Blues4U you very much sound like you know more than your average bear about bearings.
Correct that one cause of false brinneling is caused be vibration while stationary. True brinneling is caused be straight overload, impact or loading while misaligned. I cringe when I see someone pulling out a hammer during a bearing install!
Normal bearing failure is by coarse grain spalling (subsurface fatigue) in the rollers/balls/needles and races. This is much like potholes. These you can hear coming on and will slowly get louder with use.

@hemihotrod66 I suspect the vehicle rotation rule is more about keeping the grease circulated, seals rewetted and tires moved.

Funny enough, all the stuff I did to bearings growing up (mixing greases, spinning them up with the air hose, hammer installs) was no bueno, but it seemed ok and fun at the time.

 

A couple of things:
Most airplanes are stored outside and tied down. When the wind blows it will “ wiggle” the airplane and possibly cause problems with the wheel bearing.

Now for my question! Could you explain to me why over greasing bearings is considered a bad thing! In my business, when I had a business, I replaced many ball bearings on spindles. The failure rate was too high for me. Every failure , in my opinion was lack of grease because when I inspected the bearing, there was no grease! So I opened one new sealed bearing and there was just a dab of grease in between the seals! So I started opening every bearing and packing it full with my special brand of high grade grease! I never had a failure with any of my repacked bearings.
Any thoughts on this would be appreciated!






Bones

 

This is my area of expertise (as a lubricants/grease supplier). Over greasing a bearing is bad because it causes heat. As grease heats up, when it exceeds the dropping point of the grease seperation of the oil from the thickener in the grease will occur causing the oil to run out of the bearing, after that there is a lack of lubrication of the bearing, followed by even more heat, and eventual failure. Keep in mind that grease is ~85 - 90% oil and 10% thickener; the thickener is required to hold the oil so it is available to lubricate the bearing. The dropping point is the temperature at which oil begins to seperate from the thickener. The dropping point is different for different types of grease, and even for different brands of the same type of grease. You should use a grease with a dropping point around 200* higher than the highest consistent operating temperature of the bearing. Wheels wih disc brakes require a higher dropping point than wheels with drum brakes as the disc brakes will induce more heat into the bearings. Hope that makes sense.

As an example, someone earlier said they like Chevron Starplex II grease, here's the data sheet for that grease:
https://cglapps.chevron.com/sdspds/PDSDetailPage.aspx?docDataId=508167&docFormat=PDF

Note the dropping point = >250C (or 482F). That's a good high temp grease, with a lithium complex thickener. That's a good recommendation for wheel bearings, especially with disc brakes.

 

So, there’s no “ sliding” of the bearing, instead of rolling! I have heard all kinds of things and am not sure what’s what! It has been my experience, that bearings don’t usually fail quickly if they have grease, but will fail quickly with out grease!
The wheel bearing failure that started this thread is my first greased bearing that failed way too quick. But we have determined that this failure was due to improper adjustment causing extreme load. I have replaced greased bearings that had a long life, but needed replacement.





Bones

 

It would seem that with no preload, and a little clearance, you could have sliding. But there would be little or no load on the rollers when this happens.
Imagine a wheel bearing with a bit of clearance. The weight of the car, through the spindle, will put load on the bottom rollers, the uppers will have little or none.
That's why I have always preloaded wheel bearings a little. It's also what I was shown to do way back when.