Wheel Bearing Repacking at brake reline

[LarryT]

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

[jsharkey]

Originally Posted by LarryT

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

..business should pick up in 2010

Jim Sharkey

[frankh]

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

[PCHunt]

Originally Posted by frankh

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

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.

[terrykohler]

Originally Posted by frankh

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

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.

[frankh]

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

[LifeofReiley]

Old wives tale... the grease we use today is far along the road of long life for most all bearings.

[frankh]

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

[LifeofReiley]

Well Okay... you do that. My Kubota tractor states, grease every 10 hours... Hmmm? DUNNO...

[LifeofReiley]

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