Bearings, cup to cone

[kilpicki]

the cone is suppost to stay with the cup during tire changes re pack etc. how close do you stick to this rule, if 2 wheels come in to the shop for tire cx or NDT and the 4 bearings are in a pile do you change all 4 cups and scrap the 4 bearings all the time?

[iflyforpie]

I always mark them or arrange them in a way so the bearings will go in the same places as before.

If I am taking out bearing cups, I will pair them with their bearings. If I am turfing one, I turf the other. On my A/C, bearings are on condition items.

[GyvAir]

I've seen people mix them all up before and no harm appears to come of it; 200/400/1000 hours later, no higher than normal wear/rejection rate.
I would say it's only really a concern if they are already scrambled and you can see damage to either a cone or a race but the half that it was paired with prior to disassembly doesn't have readily detectable damage by which to identify it. Now which mating piece do you replace, or do you just change out the half you can see is bad?

[Colonel Sanders]

people mix them all up before and no harm appears to come of it

I was going to say that, but I tire of being attacked by
donkeys. As in previous threads, I will expect people
will be reported to Enforcement for holding this opinion.

Anyways. I try really, really hard when I take something
apart, to always put it together exactly the same as it was
before. For example, mixing up pushrods is not smart
when changing jugs. See "Lycoming dry tappet clearance".

However, it's simply not always possible, for a variety
of reasons. For example, there's that guy in Australia
right now, selling a 2001 Pitts S-2C which is completely
disassembled. Oh boy. He even mentions in the
advertisement that the engine parts have corroded
since it was disassembled since "water damage"
some years ago

[iflyforpie]

No, I'm pretty sure no harm would come from mixing them unless you wind up replacing more than you need to because the bad race and bearing mixed up. Usually it is lack of grease, corrosion, or brinneling from lack of activity that brings them to an end. Still, the OCD/AR aspect of most AMEs like to have everything arranged neatly and returned to their proper spot. There are many aircraft where even screws must go back in the same spot.

But really, even mixing pushrods isn't bad. When you change a jug they don't come with matching pushrods, do they? Always check your dry clearances (which usually have a ridiculously huge tollerance) before closing it up. Mixing rocker arms (parallel valve) can be bad because the exhaust valve has the oil jet, and the book says to keep lifters in the same spots for consistent cam and/or lifter-to-body wear.

[GyvAir]

I'm pretty OCD or detail oriented when it comes to maintaining position and orientation of parts during maintenance. Except when rotating tires and such, I guess, but that still requires the same attention in reverse. Removing all the races from a set of wheels because the cones where mixed up though would cause more damage than good, for sure.

I remember a kid in high school tearing down some V8 engine out of his car for a shop project, just to see what condition it was in. Put it all back together using all the original parts, but paying no attention to where the bearings were reinstalled. Couldn't even turn it over, it was bound up so tight. He spent about a month of Sundays of trial and error, rearranging all the bearing halves until it didn't feel too bad rotating, put it back in the car and motored on. Don't know how long it lasted, but he definitely ran it for a few years after that.

Panel screws.. wouldn't you think that when installing screws, one would notice that if one screw only took 2 turns before it torqued up and another one took 15 turns and then shanked out, that maybe there's something wrong with the picture? I find it disturbing how often I find panels installed this way.

When do you take delivery of* your Pitts-in-a-box, Colonel? Sounds like a worthy project!

[Colonel Sanders]

delivery your Pitts-in-a-box

Jesus, don't even joke about that.

[kilpicki]

our wheels are on cycles not hrs and require ndt at a given number of cycles. as the whole fleet was converted more or less at the same time and the fleet cycles are close to ndt time I noticed the last few in for tire changes had noticeable worn cups, I suspect its the lack of matching the cones.

[GyvAir]

Not quite scientific method, but it would be interesting if you could keep the new cones and races matched for the same number of cycles now and see if the wear improves over random reassembly.

[Colonel Sanders]

By around 1778, Honoré Blanc began producing some of the first firearms with interchangeable flint locks, although they were carefully made by craftsmen. Blanc demonstrated in front of a committee of scientists that his muskets could be fitted with flint locks picked at random from a pile of parts.

[robertw]

I used to work in a component shop overhauling helicopter dynamic components. Keeping bearing inner and outer races (cups and cones) matched is extremely important in an overhaul shop environment. The component repair and overhaul manuals in many cases specify that it is necessary and as well, bearing inner and outer races are individually serialized to indicate that they are a matched set. These types of bearings are measured for radial run out down to .00001" of an inch, making not only the races being matched important, but also the positioning of the inner race relative to the outer race during installation. We made it shop practice to keep everything matched even if the manuals did not specify that they should be. When it comes to drive train components that operate under extremely high RPM's and loads, keeping things matched is a necessity.

When you're talking about wheel bearings on a C-172, or something of that type (which I've dealt with too), the manuals make no mention of caution when it comes to wheel bearing races. Most of the wheel bearings in GA aircraft can be bought at auto parts stores as commercial parts anyway. They are not precision bearings. It's my opinion that in this application, you shouldn't be worried if inner and outer races get mixed up. The manuals don't call for it, so it's not necessary. I've never seen a wheel bearing degrade because the matching race was not installed.