bearing pre load, hubs, headset and adjustable bbs
 

so i work in a shop. during assembly we adjust the hubs, 1 piece cranks, headsets etc. they want me to set the preload of the bearings pretty high, i can feel notchyness at the end of the handle bars for headsets. for solid axles they want notchy feeling axles when spun by hand. surprisingly qr wheels are adjusted properly with slight play in the axle when not clamped. i learned that bearings should have only enough preload to get rid of any play. they say that the high preload is so that customers wont experience loose headsets and hubs. i thought the 'free' tune up that every bike gets is to cure these break in issues. so what are you thoughts? high preload bearings to keep the customers happy or cost cutting so customers dont return and clog up the service dept?

You're right, excess preload increases bearing wear. Some preload beyond just taking out play is proper, but excess preload is the same as running a bearing with a load higher than it's rating, and will increase not only rolling friction, but shorten bearing life.

There is no real break-in period for bike bearings, other than some relaxing of the seals, if any, so you should adjust the bearing for what's correct now, and not try to factor future changes in.

Possibly an exception can be made for headsets, whose crown races or head cups may not be fully seated. These will loosen a bit over the first few weeks as the cups settle, and need re-adjustment. But even here I don't think you can solve the problem by overloading the bearing. Either go the extra mile to make sure all is seated, or tell your customer what to expect and deal with it as it arises.

I'm coming short of declaring shenanigans on this shop. Sounds like management wants to rig less expensive bikes to break down prematurely, creating business for the service bay. Sounds harsh, but such underhanded practices do happen.

At least the other bearings are rotating and therefore have the lubricant replenished as they turn. But setting up headsets with that much preload seems like a recipe for quickly developing wear that creates the 'indexed steering' symptom.

BTW, another pet peeve I have with most bike shops is the way they adjust the brake cables. The adjustment screws are turned all the way in and the cables are pulled as tight as possible so the pads are just barely clearing the rim. Fine as long as things stay in perfect adjustment, but if the rim goes the least bit out of true or the brake doesn't quite center then there's no longer a quick fix by using the adjustment screw to loosen the cable.

thankfully we adjust our v brakes so that the noodle has just enough slack to be removed. same for the release on canti brakes. the whole preload thing irks me though. i dont adjust them like that with high preload though but that is what the boss wants.

That's what the 1st tune/1st warranty checkup is supposed to do - catch things like that after a new bike gets sold and within the initial "break-in" period. What the OP's shop is doing is either purposely or ignorantly forcing bad assemblies. This is one of those things that separates a good shop from a bad one.

It doesn't sound like your shop places too high a priority on assembly quality. This is one of those things you may or may not want to push as a shop issue - if you have enough seniority or rank to effect any changes.

To offer some explanation for those things - customers usually squeeze brakes on demo bikes as the very first thing that they do - "tight" feeling brakes seems good even if it doesn't actually mean the optimal setup in terms of riding. Adustment screws all the way in may speed up warranty tune up turn-around.

All headset bearings are not the same. Angular contact, cartridge bearing, integrated models require a fairly large preload, but a conventional caged ball headset is much more sensitive to a small amount of excess preload.

I prefer to judge the play in hub bearings by trying to move the rims side to side, up by the brake pads. Even a small amount of clearance multiplies to a significant slopiness at that point. Cheap hubs can't be adjusted as closely. Some of those cup and cone hubs have cups that are not precision ground. The bearing play can go from too tight to too lose as you turn the wheel.

Simply put anyone that would "preload" precision bearings, really dont understand the science of bearings.

Jobst Brandt wrote that cup and cone bearings should be preloaded until they have a "slight lumpy drag".

If a tiny little skewer has the force to compress an axle enough to take play out of bearings, then how can it be that the weight of a rider, while pedaling, and riding over bumps, doesn't have enough force to cause the axle to spread out?

The cones act like cams-because of the angled contact, they force the axle apart.

The weight and the chain tension and other loads are constantly trying to change the position of the cones with respect to the cups.

A slight amount of preload counteracts this tendency.

When you say science you imply that you have research in mind to back up your opinion. I believe what you said is actually an assumption. If you claim to have science, i.e. research on your side, please tell us where we may read up on it.

I think the opposite is true. Preloading is the norm.

I recently took apart a Craftsman router, built in the mid 70's. The last time I tried to use it, it squealed like crazy. The motor runs at 25,000 rpm. The top bearing was a 608, the same size found in Mavic hubs. The bottom bearing was a 6003 - once again a common bicycle bearing size. I bought new Enduro bearings and put it back together - including the wave washer that preloads the bearings - much the same as the wave washer found in Campy UT cranks.

Some hubs, like power tap, also use a wave washer to preload the bearings, so there is no bearing adjustment that can be done.

Many authors say to just take out the slack. Despite what I said, I believe their bearings are more or less in good shape.

This is because many people check their cone adjustment in the bike and it's not so precise.

If you take out all the slack this way, you get a bit of preload.

Because you are just not likely to find the EXACT POINT of adjustment where there is EXACTLY no clearance but EXACTLY no pressure either.

Well, it's good to hear your shop at least makes the effort to check the hubs, bottom brackets, and headsets on bike builds instead of just throwing them together as is.
I think I'd rather have the adjustment a bit too tight rather than a bit too loose.