# Bearings - Failure due to Excessive Preloading



## ruger (Jan 12, 2011)

First, I’m an engineer in the bearing business for many years. My staff and I perform bearing life/failure analysis daily. We supply products into many industries including aerospace, consumer products, sporting goods and of course bikes. I ride as a recreation and often take my bike with me on work trips.

I recently had a guy – a professional in the industry - hand me a failed bearing from a bike. He said, “This bearing failed after only a few months and is crap.”

INPUT DATA
1)	The bearing is a deep groove ball bearing with seals on both sides and the manufacturer is unknown.
2)	The bearing failed after a few months
3)	When holding the bearing in my hand and spinning it, it felt “crunchy” as if there was contamination in it.
4)	Taking off the shields I noticed there was plenty of grease and the grease was good, but had turned black in color.
5)	After cleaning the grease out the bearing looked intact and OK.
6)	After taking the cage out and removing the balls I looked at the raceway of the inner and outer ring.


ANALYSIS
Look at photo of the raceway under magnification. Notice that the right side is smooth and shiny – that’s a perfectly good raceway and that is what it should look like. Look at the left side and notice it’s all rough. In the bearing world we call this “spawling.” The raceway was worn prematurely due to excessive loads.

CONCLUTION
When this bearing was installed there was too much axial preload. I determined this becuse only one half of the raceway is bad. Axial preload is typically applied to a bearing by tightening a nut/screw on the axle that goes through the bearing. Adjustable preload on hubs and other parts of the bike has become a desirable feature these days. However, there is a very fine line between the proper amount of preload and too much preload.

Depending on the threads of the nut/screw, too much preload can be applied with as little as 1/60th of a turn. The load/deflection curve on a bearing spring rate is X². As an example, 10 pounds of preload is applied by turning the nut/screw 1/60 of a turn after tightening up the slop. An additional 1/60th of a turn could result in 100 pound preload – just an example.

Preload is a load. For example, say the rider weighs 200 pounds and the 200 pounds is what the bearing load is. Over preloading the bearing mathematically makes that same rider now weighing 500 pounds. It is that simple. 

If you have a bearing from your bike that looks like this photo, you know why.

If this type of analysis is helpful I would be happy to show other analysis in future threads?


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## bikerjulio (Jan 19, 2010)

From what part of the bike was that bearing?

From my reading of posts related to bottom brackets with spacers and wave washers, ie BB30, it seems there are plenty of people who have not grasped the concept of correct installation. Just put on the crank, torque it up and all will be OK, right?


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## ruger (Jan 12, 2011)

bikerjulio said:


> From what part of the bike was that bearing?
> 
> From my reading of posts related to bottom brackets with spacers and wave washers, ie BB30, it seems there are plenty of people who have not grasped the concept of correct installation. Just put on the crank, torque it up and all will be OK, right?


I would rather not disclose details of the work I did proffessionaly. I will say this is from a road bike.

bikerjulio - you are right on the money with your "grasping the concept" comment. Using the latest technology I'm trying to show how to resolve and prevent bearing failures.


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## FBinNY (Jan 24, 2009)

Ruger,

Thanks for the benefit of your professional analysis. There's lots of confusion regarding how much to preload a bearing, partly resulting from folks not knowing the difference between radial and angular contact bearings. 

Other issues include excess axial loading in hubs because of axles flexing due to non parallel dropouts and/or the added compression when QRs are closed.

Hopefully your post will remind folks that bearings have to be adjusted and run consistent with their design and rated capacity.


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## jwp3476 (Jun 22, 2010)

I also managed to "eat" a set of bearings with too much preload on the front wheel. After replacing the bearings, I carefully set up the preload with a little bit of play and installed the wheel. The wheel didn't seem quite as free as I thought it should be. I relaxed the tension on the skewer and the wheel freed up. Bottom line was the skewer can increase the preload on the bearing so it must be set somewhat loose initially.


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## Kerry Irons (Feb 25, 2002)

*Spelling*



ruger said:


> In the bearing world we call this “spawling.”


Actually, it's spelled spalling. As in "Spall are flakes of a material that are broken off a larger solid body" Just saying.


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## boneman (Nov 26, 2001)

*Sure, keep them coming*

It would be helpful if you indicated whether it came from the BB, hub, etc. location.


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## C-40 (Feb 4, 2004)

*which may explain.....*

Why some hubs, like PowerTap and both Campy and FSA cranks use a wave washer to prevent overloading the bearing.


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## apoint (Nov 22, 2010)

I always thought cranking dn on skewers was a bad idea for bearings.


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## reptilezs (Aug 21, 2007)

apoint said:


> I always thought cranking dn on skewers was a bad idea for bearings.


preload should be set with the qr clamped


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## jwp3476 (Jun 22, 2010)

FSA cranks have no adjustment so the wave washer is supposed to take up any slack if the BB is a little too small. Of course there is another issue with FSA if the BB is a little to wide - wave washer or not the bearings get fried.


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## MR_GRUMPY (Aug 21, 2002)

Isn't this a case of Brinelling?


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## apoint (Nov 22, 2010)

I was told by a LBS mechanic last week that he could hammer in the FSA crank into my shimano bearings to make it fit. Hope that dude never works on my bike.


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## Kerry Irons (Feb 25, 2002)

*Makes me fret*



MR_GRUMPY said:


> Isn't this a case of Brinelling?


Brinneling is denting, as your image shows. What is happening in the case described by the OP is properly called fretting, where metal is actually removed as opposed to just leaving a dent.


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## danl1 (Jul 23, 2005)

apoint said:


> I was told by a LBS mechanic last week that he could hammer in the FSA crank into my shimano bearings to make it fit. Hope that dude never works on my bike.


Meh. It takes a pretty good whompin' to get an FSA crank into an FSA bearing. 

The mega-exo and Hollowtech II internal diameters are the same. There are other (ie width) reasons that they aren't necessarily compatible in every case, though. Better to use the right bits and not worry about it.


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## apoint (Nov 22, 2010)

danl1 said:


> Meh. It takes a pretty good whompin' to get an FSA crank into an FSA bearing.
> 
> The mega-exo and Hollowtech II internal diameters are the same. There are other (ie width) reasons that they aren't necessarily compatible in every case, though. Better to use the right bits and not worry about it.


I believe your wrong About FSA crank is the same diameter as shimano. Several mech, have said sram is a hair larger than shimano as far as the bb86 is concerned.


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## apoint (Nov 22, 2010)

reptilezs said:


> preload should be set with the qr clamped


 Dont matter. Very high QR pressure is pushing in on the bearings.


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## -dustin (Jan 11, 2009)

apoint said:


> I believe your wrong About Sram crank is the same diameter as shimano. Several mech, have said sram is a hair larger than shimano as far as the bb86 is concerned.


He didn't say SRAM,...


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## Fredrico (Jun 15, 2002)

*Back in the good old days...*

Shop mechs always used to preload bearings, that is tighten the adjustable cup an 8th of a turn beyond the point where there was no play if you shook it with your hands. It took about one year, 8000 miles, for a nice Campy Super Record BB to become trash as a result. I replaced it with an identical BB, and have yet to change it, 65,000 miles later. Wheel hubs have proven to be the same. I can't wear mine out. They're all still fine, after 65-75,000 miles, because I never preloaded the bearings, only adjusted out the play.

Now hearing more horror stories of modern uber lightweight hubs and BBs, I'm even more skeptical of the durability of sealed, non-adjustable bearings. All you can do is pop them out, install new cartridges, and hope for the best. :shocked:

I'm also shocked that almost all the bikes I've assembled at a LBS came out of the box with wheel bearings not adjusted at all. They're just slapped together in the factory and skewered on the bikes. When you spin them in your hand, they all feel rough. A couple of years later, they come back with the races totally trashed, and everybody thinks that's normal. Same with cheaper BBs, the adjustable ones. They're always way too tight, but nobody bothers to take out the "preload," if that's what it is, and they turn like molasses.


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## ruger (Jan 12, 2011)

Preloading a deep groove ball bearing always increases life if the preload force is correct. All deep groove ball bearings have clearance. That means the balls are not touching the raceways – there is a slight gap. When the axle goes through the bearing and a radial load is put on the bearing, the balls on the bottom of the bearing are in contact and the balls on the top are floating – not in contact. In this condition the bearing spins and the balls go in and out of the contact zone as the bearing rotates. As the balls go in and out of the load zone they skid and this degreases life.

Applying an axial load via preload adjust or wavy spring pushes all the balls into the load zone. There is no more skidding and life increases. Wavy spring washers are excellent for pushing low forces below 15LBS. Most applications requiring low axial preloads are best solved with wavy springs. Hubs are a good example of needing a low force where such springs can be used.

When trying to increase life all you want to do is push a low load so the balls are always in the contact zone.


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## Fredrico (Jun 15, 2002)

*I've never worked with wavy springs.*



ruger said:


> Preloading a deep groove ball bearing always increases life if the preload force is correct. All deep groove ball bearings have clearance. That means the balls are not touching the raceways – there is a slight gap. When the axle goes through the bearing and a radial load is put on the bearing, the balls on the bottom of the bearing are in contact and the balls on the top are floating – not in contact. In this condition the bearing spins and the balls go in and out of the contact zone as the bearing rotates. As the balls go in and out of the load zone they skid and this degreases life.
> 
> Applying an axial load via preload adjust or wavy spring pushes all the balls into the load zone. There is no more skidding and life increases. Wavy spring washers are excellent for pushing low forces below 15LBS. Most applications requiring low axial preloads are best solved with wavy springs. Hubs are a good example of needing a low force where such springs can be used.
> 
> When trying to increase life all you want to do is push a low load so the balls are always in the contact zone.


I think I know what you mean. But with traditional cup and cone bearings, simply taking out the play, from my experiences, is all the "preload" a high quality bearing needs. Wouldn't you feel a "gap" as you describe, on the upper, unloaded ball of an axle bearing by shaking the wheel laterally in your hand? It's always worked for me, in Campy cup and cone BBs and hubs, as well as current Shimano Ultegra adjustable cup and cone hubs. The top bearing, the one over the axle, is not unloaded to the extent it loses contact with the upper race and a gap forms. That's what you mean by preload, right? Only the really cheap ones wiggle in the dropouts if you merely take out the play in your hand, so you have to tighten them slightly more, what we used to refer to as preloading.

What I've seen over the years, is preload taken to extremes, with bearings adjusted so tight they actually "bind" when you turn them. I know some of that is the rubber washers to seal out water, but I've encountered many adjustable bearings that are way too tight, and wear out 10 times faster than they should.


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## C-40 (Feb 4, 2004)

*Campy...*

Campy is smart enough to specify and exact range width so that doesn't happen 67.2-68.8mm. Whether FSA cranks still suffer would depend on the wave washer's range of adjustment.


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## apoint (Nov 22, 2010)

-dustin said:


> He didn't say SRAM,...


 My bad, I got Sram on the brain. I changed it to FSA. Sorry.
Again, for my bb86 the Fsa is a hair too thick to fit properly in the bb86 bb.. It has to have the FSA bearing to go with the fsa crank..


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## durielk (Jan 8, 2011)

Since we are all talking BB & I am about to spring for one. They list so many critical sizes, 68mm wide BB30 shells with 42mm ID & no threads (FSA K-Force). Will this fit on a standard BB after removing the ultegra crank? Time 2009 Speeder bike has threads down there that the utlega BB went into.


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## C-40 (Feb 4, 2004)

*no...*



apoint said:


> Dont matter. Very high QR pressure is pushing in on the bearings.


A lot of hubs can be adjusted with the QR tightened. If the adjuster is set properly, there is no QR pressure on the bearings. The bearing play can also be set far too loose.


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## Weav (Jun 21, 2009)

I'm interested in this topic but totally lost. I have a new pair of DA 7850SL wheels, have not done anything to them since receiving them regarding bearing adjustment. Is this something I need to look into? How can I tell if mine are set correctly? Like I said they haven't been touched since leaving the factory. Thanks.


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## orange_julius (Jan 24, 2003)

Weav said:


> I'm interested in this topic but totally lost. I have a new pair of DA 7850SL wheels, have not done anything to them since receiving them regarding bearing adjustment. Is this something I need to look into? How can I tell if mine are set correctly? Like I said they haven't been touched since leaving the factory. Thanks.


If you notice some play in the hubs, then you need to tighten the hub a bit. With the wheels mounted, use your hand and try to move them side-to-side. If you notice play, bring it to an LBS. I've had to tighten the rear hub of a new Campag wheelset a bit. 

An over-tightened hub is a little harder to detect, however ...


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## goodboyr (Apr 19, 2006)

*Campy/Fulcrum Hubs*

Interesting discussion. My practice has been to adjust preload on these hubs till there is just a very tiny bit of free play with the skewer tight. Then, when your weight is on the bike, that extra bit of loading takes the rest of the free play out. So far lots of miles on mavic, fulcrum and new zipp wheels with no bearing issues.


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## GirchyGirchy (Feb 12, 2004)

goodboyr said:


> Interesting discussion. My practice has been to adjust preload on these hubs till there is just a very tiny bit of free play with the skewer tight. Then, when your weight is on the bike, that extra bit of loading takes the rest of the free play out. So far lots of miles on mavic, fulcrum and new zipp wheels with no bearing issues.


There should not be any free play with the skewer tight. Free play should be present when the skewer is loose so that it takes up the play when on the bike.


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## C-40 (Feb 4, 2004)

*depends...*



GirchyGirchy said:


> There should not be any free play with the skewer tight. Free play should be present when the skewer is loose so that it takes up the play when on the bike.


With hubs that can be adjusted with the wheel mounted in the bike and skewer tight, it doesn't hurt a thing to have a small amount of freeplay at the rim. Wiggling the rim back and forth, near the brake pads magnifies the amount of freeplay at the axle. It's not necessary to have zero play. Taken too far, you'll load the bearings and could create more wear than a little play would cause.


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## reptilezs (Aug 21, 2007)

free play means ball drop and excessive loads on 1 ball


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## Fredrico (Jun 15, 2002)

*Agree*



reptilezs said:


> free play means ball drop and excessive loads on 1 ball


I've experimented with high quality Campy hubs. First I left a tiny bit of play in the adjustment, then mounted it in the dropouts. The play was still there.:shocked: So I took the play out, another 16th of a turn. I could feel no play spinning the wheel in my hands. Clamping it in the dropouts, it spun as freely as in my hand. I concluded with high quality hubs, putting pressure on the lock nuts and cones by the quick release skewer had no effect on adjustment. 60,000 miles later confirms this. The races are still polished and smooth, with no pitting on the races or cracks in the balls. :thumbsup:

I've had the same success with two fully adjustable cup and cone BBs with over 60,000 miles on them each. Setting them up has always been a snap, no preloading necessary. I just took out the play turning the spindles in my hand. With cranks mounted I could still feel no play, even whacking up hills in big gears. I was actually quite impressed with Campy BBs after that. Previously I had to tighten some old Shimano cup and cone BBs beyond the point of no play, because I could feel play when the cranks were mounted.

With good stuff, like Campy, I now believe preloading beyond simply taking out the play is way overrated and leads to bearing failure, as my early experience mentioned above. I also believe, owing to the longevity of my wheels, there is little if any additional preload on bearings when clamped into the dropouts.  Axles, cones and locknuts are generally made of CRMO steel. They're very hard, and IME, don't compress under QR pressure. Maybe the current stuff does, with sealed cartridge bearings press fitted into the hub shells, I don't know.


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## Kerry Irons (Feb 25, 2002)

*Ding ding ding!*



Fredrico said:


> I've experimented with high quality Campy hubs. First I left a tiny bit of play in the adjustment, then mounted it in the dropouts. The play was still there.:shocked: So I took the play out, another 16th of a turn. I could feel no play spinning the wheel in my hands. Clamping it in the dropouts, it spun as freely as in my hand. I concluded with high quality hubs, putting pressure on the lock nuts and cones by the quick release skewer had no effect on adjustment. 60,000 miles later confirms this. The races are still polished and smooth, with no pitting on the races or cracks in the balls. :thumbsup:
> 
> I've had the same success with two fully adjustable cup and cone BBs with over 60,000 miles on them each. Setting them up has always been a snap, no preloading necessary. I just took out the play turning the spindles in my hand. With cranks mounted I could still feel no play, even whacking up hills in big gears. I was actually quite impressed with Campy BBs after that. Previously I had to tighten some old Shimano cup and cone BBs beyond the point of no play, because I could feel play when the cranks were mounted.
> 
> With good stuff, like Campy, I now believe preloading beyond simply taking out the play is way overrated and leads to bearing failure, as my early experience mentioned above. I also believe, owing to the longevity of my wheels, there is little if any additional preload on bearings when clamped into the dropouts.  Axles, cones and locknuts are generally made of CRMO steel. They're very hard, and IME, don't compress under QR pressure. Maybe the current stuff does, with sealed cartridge bearings press fitted into the hub shells, I don't know.


I did this same experiment back in the 90s with Campy C-Record hubs and found that tightening the QR skewer VERY tightly was the equivalent of tightening the cones by 1/36 of a revolution of the cone wrench. IOW, virtually zero change. I did the same experiment on some cheap Shimano hubs on my hybrid commuter bike and there was a lot more change due to tightening the QR skewer. I completely agree with your conclusions and analysis!


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