Bicycle Mechanics - Dodgy BB with seized bearing - can it rob you of power?

Hi all !

Ride a Specialized Allez Sport 2010. Sora compact chainset, Hollowtech II BB.

Bike developed a nasty groaning noise, twice every crank revolution so making a noise on each pedal stroke (ie on both left and right).

Disassembled the crank and bottom bracket completely with the intention of re-greasing and re-tightening everything (including pedals). One thing I spotted once I had it out was that the bearing on the drive-side is grinding and close to seizing up. Holowtech II so it's one of those external bearing BB cup jobbies. Guess the closed cartridge seal isn't quite as sealed as it should be. It is probably something to do with riding on gritted roads this winter and then not having time to wash down properly.. ;) A lesson learned, and 3 cans of GT85 purchased from LBS.

Anyway, these sealed cartridges can't (or shouldn't) be disassembled and serviced, so have picked up a Shimano 105 5700 BB (slight upgrade) for reasonable money from LBS.

Question is this - what effect would a ropey drive-side BB bearing have on pedalling efficiency if it was close to seizing? Will this have been robbing my back wheel of valuable watts?

Ta,
Rich.

It will rob you of power, but probably in amounts that you wouldn't notice. Depending on speed, 95-99% of your power goes to overcome wind resistance which rises in proportion to the square of your speed, while bearing, chain and tire drag are constants.

The real issue of riding with a seized or stiff bearing is that the inner race will slip on and wear the spindle, costing you a spindle (or right crank) and if it scores it deep enough possibly a failure and injury.

Unless it is REALLY stiff as it should be in an almost seized condition then no, you won't feel anything. If you don't feel resistance when you spin the bearing by hand then it's only a matter of noise and premature wear from the extry of water and grit. With the abrasive quality of such a mixture it's more likely that the bearing will wear and produce slop than it would to seize up. Or at least it would only be tight until the grit wears the steel enough to allow for a sloppy fit.

When you wash down your bike keep in mind that the spray from the hose should not be a hard spray. You want to use a soft shower spray such as you'd use on delicate garden plants. Anything more harsh and you risk blowing water in past bearing seals. This happens because for our bicycles we don't want a firm sealing action as it's too draggy. So the seals only have a light contact. A contact pressure that a properly directed forceful blast of water can blow past to enter the bearing.

They are radial bearings pressed into the adapter. They can be serviced by popping out the seal and cleaning and relubing. The seals in our bearings are dust seals, not meant to keep out water.
The tool to replace the bearings. http://www.enduroforkseals.com/id114.html and how to use it. http://www.enduroforkseals.com/sitebuildercontent/sitebuilderfiles/puller_press_tool1.pdf

But if grit got in and has produced a rough feel and gritty sounding bearing then the damage is already done and it needs to be replaced.

Wouldn't hurt to gently pop off the bearing seals and use a needle-tip on grease-injector to add more grease. I like to push the needle to the seal on the far side and squirt until it bubbles up through the bearings. Re-install seal, spin around a couple turns and wipe off the excess.

I also like to use a little blue Loctite when installing the spindle through the bearing to help stick it to the inner race. This will prevent any fretting and wear between the race and spindle in the event your bearing starts to seize up. Also solves a lot of mysterious squeak and noises when the fit isn't tight (the spindle should require some force to push through bearings).