Boxerworks.com

Chuey wrote:When this was recently discussed here, the consensus was that a slightly loose bearing would last longer than a slightly tight one.

My take is just the opposite chuey. Did you mean that the way you said it? I thought the concensus was that a properly preloaded bearing will last longer than a loose one.

I know Duane has continually made the point that even an overloaded tapered roller wheel bearing will last a very long time.


Ken

A bit too loose is better than a bit too tight (at least as far as wheel bearings are concerned).

How to describe "loose" is my question. Cars have that adjuster with the cotter key to hold the final adjustment in the funny nut. Those bearings are not neutral, they are loose by any standard. They last just fine.

Actually, these bearings are so over rated for the application that it is very hard to damage them by improper installation. What happens is when they are too tight, they over heat and spin in the hub and ruin it.

I don't like loose bearings on my bike and prefer a bit of preload. The factory sent them out with too much preload and that WAS a problem.

Not sure whether bearing preload should be considered as "not liking loose and preferring a bit of preload", when we hear of people with catastrophic wheel bearing failures on the road. So here's a bit more scientific approach for explaining bearing preload, what it does and what it means:

http://www.promshop.info/cataloguespdf/kbc10.pdf

BMW doesn't say zero play, they don't say "a bit preload at your leisure is fine", they have defined a value, at least for swingarm and headstock. I apply the same philosophy for the wheel bearings.

StephenB wrote: BMW doesn't say zero play, they don't say "a bit preload at your leisure is fine", they have defined a value, at least for swingarm and headstock. I apply the same philosophy for the wheel bearings.

Swingarm and headstock bearings will not overheat and spin in their hubs. Thus, I would never assume that the spec for them would be applicable to wheel bearings. While the bearings can be the same, the application makes all the difference.

StephenB wrote: BMW doesn't say zero play, they don't say "a bit preload at your leisure is fine"

Only experience gives you a 'feel' for bearings, torque values, valve clearances, etc.
If you are unsure of your personal skill level, ALWAYS do exactly what the book says so nobody can blame you if it fucks up.

My personal experience has proven that 0+ a film of grease is usually ideal,
actually, I can't think of any particular instance when it's not.

1 thin film of grease for non-spinning bearings (steering, swing arm).
2 thin films of grease for wheel bearings.

What BMW says and what they did are two different things. Nearly all wheel bearing issues are not a failure of the bearing, but a failure of the preload causing the race to spin and ruin a hub.

A neutral preload wheel bearing in a BMW motorcycle wheel is not going to fail early. It also will not generate excessive heat that causes it to spin in the hub.

I still say that I prefer a bit of preload. I like the "shake the wheel test" to give me about 15 lbs on the nut. I can tell you for sure that that test is the only one that gives a reliable number. All of the others that I have seen are fraught with errors. Setting up the preload in a stack outside of the hub, as shown in the BMW shop manual, is just crazy.