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MG Midget and Sprite Technical - Bearing thrust faces.

Sorry to be a pain and to bring up the 'B' word again but I've got a question about the thrust faces on bearings.
I've always looked at the front wheel bearings and worked out the way they should face but am now wondering if my logic is flawed. I put the thicker walled face of the bearing towards the other bearing and ignored the printing on the walls of the races although I'd assumed that if the inner race had printing on it then it was to be facing inwards and if the outer ring had printing then IT should be facing outwards, as per Cessna wheel bearings. Because it is difficult to remember such rules I have abandoned them and gone for "Thick inwards, thin outwards".
Is there any documentary evidence of the correct procedure? An 'expert' on another forum says that he puts them in the opposite way to me and has never had one fail.

1/2 hour of Googling came up with nothing concrete as nobody mentions what happens if you get it the other way round.

I promise not to mention the "B" word again!
r thomas

Rob-
It can indeed be confusing, as bearings are marked differently at different times and by different mfrs. Or not marked at all!

Helps to cup your palms at 90 degrees and hold a big ball. Move your hands around to simulate loads at different angles. Your palms are the cross section of the race.

OK. The (ball) contact angle axis is from the thicker side to the thicker side, but not all bearings have differences in both races. Usually the inner race does have a distinctly different thickness, and the thick side is the low end of the axis. So the axis angle is from there across the bearing and away from the spindle axis. Or, the thicker side of the inner race of both bearings should be away from the hub centre. The contact axes look like so: < >

In this type of application, the contact axis of the two bearings should intersect OUTSIDE the hub, between the bearings. This is the most common installation of any angular contact bearing pair, including taper rollers. (In tapers, the contact axis is the perpendicular to the roller axis) This gives the lowest stress and the greatest resistance to "overturning moments" which is what you have with a load applied sideways at the tyre, resisted by the spindle.

FRM
FR Millmore

Rob

If you get them the wrong way round, the outer races of each bearing are not being clamped by anything, so are liable to move around. Not good.

From your description, it isn't exactly clear which way you are fitting them.

<<I put the thicker walled face of the bearing towards the other bearing>>

Do you mean the outer race or the inner race? If it's the outer, that's OK.
Dave O'Neill2

The only way I can think to describe it is to say that I put them in a similar way to taper rollers with the fatter end of the inner race against the nut and the fatter face of the outer race against the hub casting.


FRM Your explanation makes sense although I can't picture what happens if you have > < for your bearing fitment, if you see what I mean. This is the way one poster on this other forum is telling everyone to fit front bearings. He is adamant that fitting them this way makes no difference.
r thomas

Maybe I'm just getting old, but don't some bearing sets have the 'THRUST' marking on the outer race and some have it on the inner race (opposite side, obviously) ?
r thomas

Rob
If you do them as if they where taper rolers you are doing it correct.
But then why not fit taper rolers......(runs for cover)
Onno K

Rob,

If you look at each of the bearings, --- ignore the writing for now ---- you can see that the inner of each can be removed only one way.

When you put them in the hub, they are installed so that the inner of the bearings is being pushed into the "cup" that FRM describes.

As for the writing. If your have the word thrust on them, then that is installed so that on both, the word thrust is to the inside.

Does this picture help you?

For both bearings, the faces you see in the picture, should be installed to the inside.

Lawrence Slater

Rob-
The reversed mounting >< gives an assembly that still has large radial and thrust capabilities, but low stiffness to the overturning moments. Result is that it is not very stiff in offset thrust loading, but is somewhat tolerant of shaft deflection etc, which can be useful in industrial machinery. A "fix" of sorts for other weakness, not used much.

It is important to note from my above first post, that my < > notation is for the contact axes, not the race shape, which is reversed!
"(In tapers, the contact axis is the perpendicular to the roller axis)"
So notation would be >race< for <axes>.

In this case, reversed mounting is certainly not desirable, and the outer race clamping issue Dave gave could be life threatening. Such mountings, when used, have positive locating shoulders or caps.

FRM
FR Millmore

FRM. Yup. I've got the <> Vs >< thing in my head now. I'm not sure what the significance of having the intersection of the <> outside of the hub is but I imagine it is to ensure that the experienced loads in any plane are evened out to reduce the chance of failure in one particular way. Not too important for me to understand this, I guess.
Having the bearings installed the other (wrong) way round, would they run the risk of losing the whole hub during any phase of driving? He, the resident expert/troll, says that he can have either both thrust faces pointing inwards or both pointing outwards since one will be always be taking any applied load. Perchance that is OK for 100% in/out sideways cornering loads but not a mix of cornering/bump/steer/roll?

I'm starting to lose the ability to put my thoughts onto the keyboard, if you see what I mean!


PS Thanks for taking the time to help. It is always so nice to know that there are people on here willing to expend effort helping to explain the mysteries of mechanical science to us.
r thomas

"says that he can have either both thrust faces pointing inwards or both pointing outwards since one will be always be taking any applied load."

There are 2 flaws in that argument. One is that, if installed properly with both thrust faces facing the inside, both bearings are taking the load, as they are supposed to.

The other flaw, is that if you put them in with the thrusts outwards, then the only thing keeping the outer raceways in the hub, is the small lip that prevents the outers separating from the inners, and the interference fit of the outer raceways in the hub.

If the lip wears, then the only thing keeping them in is the interference fit. If the outer raceways are not a tight interference fit (and some hubs aren't as tight as when they were new), then there's nothing much left keeping the outer raceways in place.

Installed with the thrust faces to the inside, facing each-other, it's impossible for the bearings to come out of the hub once the hub nut is on.
Lawrence Slater

Rob-
Yes. Installed backwards, the outer race of the inner bearing is loaded such that the outer race is pushed out of the hub, and then the inner race (cone) of the outer bearing tries to come through the hub, which is close if not clear to start - but always unpleasant. You could tell the guy to only try this on disc brake cars, because the caliper will keep the disc from going too far. Unless the disc breaks off from the bearings running cock-eyed!

You can visualize the "overturning moment" resistance much easier if you draw a simple picture in cross section. It is visually/intuitively very obvious, but hard to explain in words. Or look in a bearing manufacturer's application book.

FRM
FR Millmore

This thread was discussed between 04/08/2012 and 06/08/2012

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