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Cause of External BB Early Failure?

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Cause of External BB Early Failure?

Old 05-15-16, 10:22 PM
  #1  
DropBarFan
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Cause of External BB Early Failure?

I had to replace a Shimano FC-M59 bottom bracket after only about 2 years/4,000 km use. Replacements are pretty cheap but still I wonder why some other riders get much more mileage out of external BB's.

BB problem went quickly from slight noticeable play to alarming clank. Previously w/square taper BB's I could ride a fair # of miles after they started to go bad. Some folks say that Shimano BB cartridges are now a semi-disposable thing that should be replaced every couple of years like a chain. But if a BB goes bad on a tour it could be a hassle. Phil Wood is the gold standard for bike tourists AFAIK but a rather pricey form of insurance.

Misalignment is supposed to be the #1 cause of early failure but the BB shell was faced & BB was installed by a good LBS. Pretty sure I didn't overtighten the left-crank plastic bolt. Didn't ride that much in the rain & the busted BB looked pretty clean & greasy. Threaded rings were tight. So I'm wondering if there can be other causes of early failure?
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Old 05-15-16, 10:26 PM
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Without a torque wrench you can't know if you tightened the preload cap correctly. It can have a profound effect on durability. Were the bearings corroded?

Also, FYI the bearings are cheap and replaceable.
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Old 05-16-16, 03:55 AM
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Even slightly too much preload on the bearings in a standard external bearing bottom bracket can cause premature failure. RWC makes bottom brackets that use angular contact bearings to eliminate the issues with bearing preload. RWC OUTBOARD BOTTOM BRACKETS, ANGULAR CONTACT
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Old 05-16-16, 06:51 AM
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If you are concerned then dismantle the old BB. If they are rusty then water got in. If they are full of grit then dirt got in. If they are dry then they needed more grease.
The cartridge style bearings usually have a long life because they are well protected by the cups and BB. External bearing BBs are hanging out in all the crap.
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Old 05-16-16, 07:04 AM
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Avoiding too much preload on the bearings if why Shimano's TL-FC16 is plastic and small in diameter. Unless you use pliers on the outside edge, you really can't badly overtighten it. I always make sure the driveside is seated fully against it's bearing by smacking it with the palm of my hand or rapping it lightly with a rubber mallet. Then install the nds arm (and the spacer for a triple), thread in the compression plug and tighten it just snug using TL-FC16 and not really cranking down on it. Torque the clamp bolts evenly in stages to spec.

Done that way I have many thousands of miles on BB6700 bearings with no failures.
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Old 05-16-16, 07:15 AM
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Originally Posted by Slash5 View Post
If you are concerned then dismantle the old BB. If they are rusty then water got in. If they are full of grit then dirt got in. If they are dry then they needed more grease.
The cartridge style bearings usually have a long life because they are well protected by the cups and BB. External bearing BBs are hanging out in all the crap.
+1. Andy
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Old 05-16-16, 09:19 AM
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Frame not faced, BB shell faces not parallel?
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Old 05-16-16, 07:57 PM
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Originally Posted by dsaul View Post
Even slightly too much preload on the bearings in a standard external bearing bottom bracket can cause premature failure. RWC makes bottom brackets that use angular contact bearings to eliminate the issues with bearing preload. RWC OUTBOARD BOTTOM BRACKETS, ANGULAR CONTACT
I removed/reassembled cranks twice for travel & used a butter knife (hi-tech) in the plastic pre-load ring & didn't force it. Now I have the TL-FC16 tool & when I used it to remove the plastic ring it came off easily. BTW I was wondering about how over-tightening the plastic ring could cause bearing wear. IE wouldn't excess wear happen only if plastic ring was tightened so much that left crank was actually touching the the BB rings & thus creating lateral load on the bearings?

Thanks for the tip about RWC bb's, they look pretty interesting.
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Old 05-16-16, 08:04 PM
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Originally Posted by DropBarFan View Post
I removed/reassembled cranks twice for travel & used a butter knife (hi-tech) in the plastic pre-load ring & didn't force it. Now I have the TL-FC16 tool & when I used it to remove the plastic ring it came off easily. BTW I was wondering about how over-tightening the plastic ring could cause bearing wear. IE wouldn't excess wear happen only if plastic ring was tightened so much that left crank was actually touching the the BB rings & thus creating lateral load on the bearings?

Thanks for the tip about RWC bb's, they look pretty interesting.
Too much preload can open the seals long before it causes excess bearing load. Open seals + grit + water = short life.
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Old 05-16-16, 08:22 PM
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Originally Posted by fietsbob View Post
Frame not faced, BB shell faces not parallel?
LBS might have skipped facing the shell even though I asked for that. OTOH I see many posts about BB durability or lack thereof from cyclists who seem as if they would know to have BB shell faced. I'm a bit puzzled how basically all applicable Shimano HT2 BB's are in the $20-$30 price range. If there's one that's extra-durable I'd assume it would cost more as with the fancier after-market brands.

In old days with various square-taper BBs there seemed to be fairly std correlation between BB brand/price & durability: Campy was very good, Shimano & Sugino pretty good etc. A pricey Edco sealed BB went bad after a few months. Bought a Phil Wood for a racing bike but bike was wrecked before I could see how long the BB lasted.
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Old 05-16-16, 10:16 PM
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Originally Posted by DropBarFan View Post
LBS might have skipped facing the shell even though I asked for that. OTOH I see many posts about BB durability or lack thereof from cyclists who seem as if they would know to have BB shell faced. I'm a bit puzzled how basically all applicable Shimano HT2 BB's are in the $20-$30 price range. If there's one that's extra-durable I'd assume it would cost more as with the fancier after-market brands.

In old days with various square-taper BBs there seemed to be fairly std correlation between BB brand/price & durability: Campy was very good, Shimano & Sugino pretty good etc. A pricey Edco sealed BB went bad after a few months. Bought a Phil Wood for a racing bike but bike was wrecked before I could see how long the BB lasted.
Welcome to the new world order. Where only initial performance matters to the oem that supplied the bike. Andy.
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Old 05-17-16, 07:32 PM
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Yeah, I suppose very few bike buyers focus much on which BB comes with the bike.
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