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LarryT

Well Known Member
While twiddling my thumbs at work today, I decided to investigate the question of wheel bearing maintenance by referring to the on-line Timken Catalog.

If memory serves me correctly, the tapered roller wheel bearings on my -6A are L15101.

This bearing part no. has a C1 life (1,000,000 cycles) of 10,500 lbs.
The C90 life (90 million cycles with no more than 10% having a small spall on the race) is 2730 lbs.
The static load rating is 12,100 lbs. This is the load that would dent (brinell) the race.

For an RV-7 at gross weight assume 900 Lbs. per wheel = 450 lbs/bearing.

It would take a 27g impact on landing to brinell the race! A lot of other things would be damaged if one dropped an aircraft in that hard.

Some other statistics:

Touching down at 60 mph is about 1300 RPM, not real fast for tapered roller bearings. At 10 mph taxi speed only 215 RPM.

A 5.00 x 5 tire travels ~ 1260 revs/mile about 2x car tire sizes.

Depending on the length of one's taxi it could take almost 2,000 hrs. to reach a total number of revolutions of about 2.5 million or <3% of the C90 life at < 20% of rated load.


The only enemies in this equation are grease rather than oil lubrication (reduces life to 79% of oil bath), contamination and corrosion. Since my -6A is hangared, my conclusion is that cleaning and repacking the wheel bearings is only conservatively necessary at the time I reline the brakes.

Larry
 
Never Mind...

LarryT said:
While twiddling my thumbs at work today, I decided to investigate the question of wheel bearing maintenance by referring to the on-line Timken Catalog.

If memory serves me correctly, the tapered roller wheel bearings on my -6A are L15101.

This bearing part no. has a C1 life (1,000,000 cycles) of 10,500 lbs.
The C90 life (90 million cycles with no more than 10% having a small spall on the race) is 2730 lbs.
The static load rating is 12,100 lbs. This is the load that would dent (brinell) the race.

For an RV-7 at gross weight assume 900 Lbs. per wheel = 450 lbs/bearing.

It would take a 27g impact on landing to brinell the race! A lot of other things would be damaged if one dropped an aircraft in that hard.

Some other statistics:

Touching down at 60 mph is about 1300 RPM, not real fast for tapered roller bearings. At 10 mph taxi speed only 215 RPM.

A 5.00 x 5 tire travels ~ 1260 revs/mile about 2x car tire sizes.

Depending on the length of one's taxi it could take almost 2,000 hrs. to reach a total number of revolutions of about 2.5 million or <3% of the C90 life at < 20% of rated load.


The only enemies in this equation are grease rather than oil lubrication (reduces life to 79% of oil bath), contamination and corrosion. Since my -6A is hangared, my conclusion is that cleaning and repacking the wheel bearings is only conservatively necessary at the time I reline the brakes.

Larry
Click to expand...

..business should pick up in 2010 :)

Jim Sharkey
 
Most bearings fail for one of two reasons.

1) Corrosion

2) Too much grease..Overheats the bearing. If I remember rightly only 60% of the spaces between the rollers should be filled with grease.

Frank
 
frankh said:
Most bearings fail for one of two reasons.

1) Corrosion

2) Too much grease..Overheats the bearing. If I remember rightly only 60% of the spaces between the rollers should be filled with grease.

Frank
Click to expand...

I must say that I have never heard of too much grease being a problem. Would love to see some engineering literature, such as a published paper, on that subject.

Not sayin' it ain't so..... just wanting proof. I used to be from MO.:rolleyes:
 
frankh said:
Most bearings fail for one of two reasons.

1) Corrosion

2) Too much grease..Overheats the bearing. If I remember rightly only 60% of the spaces between the rollers should be filled with grease.

Frank
Click to expand...

Don't forget excessive end play or preload. Goal in the trucking industry was 0/0. Also, I'm not sure of any automated packers that leave unfilled space.
 
Just pick up the literature from any bearing supplier..tells you right there. I sat through many a presentation from industrial equipment suppliers..all told me the same thing
 
Really?....you maybe right, but millions of dollars are riding on the answer...but then again the establishment will also tell us running on lead free gas will destroy our engines too.

I know the accepted correct way works very well so I'll stick to that
 
But...

I also change brake pads every year too, they are too cheap :) and then I don't worry about it for another year.
 
Bearings

As an ex bearing engineer who saw the light. From my distant past most wheel bearing failures are due to corrosion, especially on trailers that are not used very often. Moisture is the killer as from the etching cause by the moisture forms a stress point as the roller runs across it and it will fatigue fail at that point. (How often do you look at your bearings and see those dark lines on the cone that match up with the roller spacing). So where does the moisture come from. My mentor explained it to me thus and I would not dispute this as he was right about everything else he taught me. As a wheel heats up in operation the air expands and exits the wheel, as it cools down it pulls air in, along with any moisture content, especially if it has been raining. When the wheel cools down as in a frost this moisture forms as tiny droplets on the bare metal in the wheel, eventually into larger droplets which then run into the bearing, and cause corrosion. To over come this Ruben John Smith (ex cataleena navagator in the pacific) recomended covering the internal bare metal of the wheel with a thin layer of grease, then the suspended moisture would not form into water droplets on the cold metal but remain in suspension as it would not form on the greased surface. We fixed many a problem with this method.

Happy flying
Rob
 
Cool... I would hope he would of thought more as to lubrication and put some thought into wear and tear of the bearings. Some of the grease and lubricants we have today are awesome in this respect.
 
Last edited:
Use Mobil 1 (red) grease

frankh said:
Most bearings fail for one of two reasons.

1) Corrosion

2) Too much grease..Overheats the bearing. If I remember rightly only 60% of the spaces between the rollers should be filled with grease.

Frank
Click to expand...

Incredible film strength, lasts forever, thus taking care of both the lubrication and corrosion issues.

I got frustrated with door hinges squeaking at home, removed hinge pins and lubed with Mobil 1. It has been 5+ years and not one of the hinges lubed with Mobil 1 grease has started squeaking again. Formerly some doors would start squeaking again in < 1 year.

There have been lots of improvements in lubrication technology in the last 50 years. It turns out that when the bean counters give engineers the opportunity improve products as opposed to ordering them to make them cheaper, the engineers succeed!

Larry
 
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