Crank Stiffness in BB

[lerouc]

Now you can deduct at least 30min off your previous race times!

 

hahahaha

[lerouc]

So what about something like this rather than the stock shimano? Stock shimano cost R375.
http://www.cwcycles.co.za/product/wheels-mfg-bb-8692-shimano

[JXV]

So what about something like this rather than the stock shimano? Stock shimano cost R375.

http://www.cwcycles.co.za/product/wheels-mfg-bb-8692-shimano

The blurb says it is better but doesn't say why its better. Stiffer shells might concievably lengthen bearing life but those bearings are not as well sealed as OEM Shimano BBs. First drop of water that lands on that seal is going through unless you keep the bearings swimming in marine grease.

 

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[JXV]

I thought it might be because I always get on my bike from the left side. I stand on the pedal and swing my body over, this puts pressure on the left hand crank every time. Maybe I should spend the rest of the year getting on from the other side as I've just replaced the BB. If the right side fails first then I know.

 

Myth buster in the making

Interesting point...maybe true. Mine fail on the left too. But I mount the bike from both sides so maybe the left side is just more exposed.....

 

I've made up a spare BB out of two old ones with failed left side bearings by transferring a still-healthy right side bearing to a left side cup.

 

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[droo]

Is it just me but why does my BB left hand bearing always fail first?

 

The LH bearing on Shimano BBs is more exposed to the elements than the RH one, which has the crank in the way. Fails first every time.

[NotSoBigBen]

The LH bearing on Shimano BBs is more exposed to the elements than the RH one, which has the crank in the way. Fails first every time.

I did surmise that was the reason earlier ????

 

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[JXV]

I did surmise that was the reason earlier ????

 

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Yeah ....seals on both sides are the same but the crank spider on right hand side shields the BB from direct impingement of dirt and/or water directed from hosepipes during washing.

 

I still think water is the real issue. Every single failed Shimano BB bearing I have stipped has had water damage (corrosion) and dirt in the bearings. Never seen broken balls, brinelling or cracked races that would indicate purely mechanical wear/overload.

 

A lot of times the outer seal has one or two small nicks or a lot of mud has packed in between the rotating plastic spacer and the (static) seal. In all cases there was dirt present and insufficient grease. So I'm calling out poor sealing as the root cause here.

 

I think these things are designed to fail. It would be easy and cheap to improve the seals but manufacturers have no incentive for doing so. Most of the options for improved sealing also involve a slight friction penalty so this might be a contributing reason why they don't try harder.

 

A small strategically placed hole of about 1mm drilled near the shoulder on the inside of the plastic spacer would enable grease to be topped up with a small grease gun - all you'd need to do is periodically remove the cranks to expose the hole.....I'm keen to try this.

 

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[droo]

I think these things are designed to fail. 

 

An astute observation sir.

 

2 options - one, get an Enduro BB. The bearings are replaceable. Two, get a King. Fully serviceable and has a grease port. 10 years from a bearing is not even close to an unreasonable expectation.

[BDF]

Yeah ....seals on both sides are the same but the crank spider on right hand side shields the BB from direct impingement of dirt and/or water directed from hosepipes during washing.

 

I still think water is the real issue. Every single failed Shimano BB bearing I have stipped has had water damage (corrosion) and dirt in the bearings. Never seen broken balls, brinelling or cracked races that would indicate purely mechanical wear/overload.

 

A lot of times the outer seal has one or two small nicks or a lot of mud has packed in between the rotating plastic spacer and the (static) seal. In all cases there was dirt present and insufficient grease. So I'm calling out poor sealing as the root cause here.

 

I think these things are designed to fail. It would be easy and cheap to improve the seals but manufacturers have no incentive for doing so. Most of the options for improved sealing also involve a slight friction penalty so this might be a contributing reason why they don't try harder.

 

A small strategically placed hole of about 1mm drilled near the shoulder on the inside of the plastic spacer would enable grease to be topped up with a small grease gun - all you'd need to do is periodically remove the cranks to expose the hole.....I'm keen to try this.

 

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I agree with your observation about water being the most common cause of damage. 

 

Your proposed grease hole: don't you think that would just make another place for dust and water to get in? Dust and water = rubbing compound...

[JXV]

 

 

.

 

Your proposed grease hole: don't you think that would just make another place for dust and water to get in? Dust and water = rubbing compound...

Shimano crankshafts have o-ring seals at the base of each arm that presses against the outside of the plastic spacer so the hole would be covered and sealed while the bike is in use.

 

Good practice to grease the inside of the spacer and the shaft before fitting. This will further resist water and dirt getting in.

 

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