deacon mark

I have an FSA sl light carbon crank with a mega expo BB. I familiar with the shimano external BB type cranks but wondered the life span in miles. I have 5500 on my Motobecane Im Spirit with no trouble but should the BB be replaced at a certain mileage? I do not have any issues the crank spins perfectly free but sometime pedaling hard I can feel what seems to be a slight vibration in the spinning as I pedal. Could just be normal sounds of the drive train but I do not fell it with my other bike that has a 105 crank and shimano BB. FSA says I need to use the 8681 but would a shimano also work? FSA claims not but I do not always trust the manufactures because they want you to buy their stuff.

I don't ride in the rain and like I said no problems so what mileage do most get? I did a search but not anything consistent to find mileage.
.

Bill Kapaun

There isn't an absolute number.
Some riders MASH much harder, while others spin away with relatively light pressure on the pedals.
Than sometimes one supposedly identical part will last a much longer time than another..
If it isn't bad don't worry about it.
When the time comes, it's a relatively minor repair.

onespeedbiker

Of the different types of bottom brackets the external BB type seem to have the poorest reputation for longevity. The problem appears to be that of contamination, so you need to keep an eye on the BB for any grittiness or play. While the Shimano external BB is warrantied for 2 years, they don't cover wear and tear. The only external BB that seems to last more than a year is the Chris King. The King requires a tool that allows you to service the BB by injecting grease into the bearings. The Chris King has a 5 year warranty and I have never heard of them denying a claim . The issue with a King BB is cost. The King costs about $100 for than a Shimano and the tool another $80. So you can by one King BB every 5 years for $225 or 5-6 Shimano BB over the same time period.

Shimagnolo

In my experience, the old tapered cartridge BB's last a decade, and the new-fangled external's last a year, (maybe 2 yrs if you're lucky).

LesterOfPuppets

I killed a Shimano UN-26 in about 8000.

I have about 20000 on a Shimano 600. I don't think I'll kill it before I die.

Granted I was somewhat harder on the UN-26 and never attempted repacking it cuzza the cartridgeness of it. The 600 has been repacked a few times.

FBinNY 

Too many variables to give you a number. But there's no percentage at all in preventative replacement of a bottom bracket, since the only thing to prevent is the need to replace the BB. The ONLY time I'd even consider replacing a still working BB is if I were planning a long multi-week trip (1,000+ miles) and I had doubts about the condition of the original, and even then it would have to be serious doubts not just an inkling.

Worn bearings have a very characteristic sound or rumble and aren't easily confused with other signs. If your crank feels smooth when spinning unloaded the vibration you feel is probably from the chain.

BTW- in my experience load and mileage aren't what kill off BBs. It's weather, water allows for rust formation etching away at the ball tracks, and doing in 2 days of sitting around more harm than 1,000 miles of hard riding could do. Keep your bearings well greased and they should outlast you.

deacon mark

FB thank you for the post that seems to clear it up. The cranks spins perfect the chain could be this little rumble I " feel" because it is not any creaky sound or definite vibration but just a little sensation.

dddd

I do bearing checks on external bb's all the time, since it seems they don't hold up so well.

I always hold the chain completely free of the crankset while spinning the cranks, and any bearing roughness really resonates through the frame.

It was mentioned that contamination kills the bearings, and it's true.
The main reason some bb's hold up better is due to better sealing.
Shimano's UN7X and UN5X bb's have earned such a solid rep by being better-sealed than any other comparably-priced bb out there. They can go 50k miles and still be smooth under relatively normal road conditions. It surely helps that the sealing surfaces are smaller in diameter than more-contemporary bb's, since their apparently tighter seal grip results in far less of an increase in rotating friction than with a larger-diameter spindle.
Shimano's labyrinth sealing designs typically seem to be more sophisticated than others imo, but it is quite a challeng to seal the bearings without excessive drag when the sealing diameter is relatively huge.

JanMM

6000+ miles/4 years on the Truvativ external BB on one of my bikes. No problems. I try not to ride in the rain/snow/mud/dirt etc, which probably helps.

zebede

Some wheres around 15,000 miles (daily commuting and I am a spinner) so far on a phil wood...still smooth as silk.

Shimagnolo

Something to consider in comparing the old tapered cartridge BB's vs external:
- In the cartridge BB, the alignment between the left & right bearings is fixed in the cartridge when it is mfgrd, and never changes.
- In the external BB, the alignment is controlled by the frame's BB shell.
i.e. if the BB shell's faces are not in perfect alignment, or if the threads are not straight, it can put the BB bearings out of alignment.

It is for this reason, that after I put the *second* set of external BB bearings in a bike in less than two years, I took the bike down to Vecchios's and had them chase & face the BB shell, before I installed the *third* set. That seemed to help, since this last set has gone about two years now.

deacon mark

Today I put the bike on the stand and then removed the chain from the chain rings. I then spun the cranks and they spin as free as you can imagine. I would assume they would go around 5 or more times all the way around smooth. Zero play and zero resistance. I guess it is the chain depending on how I push the crank and what gear I am in. I have heard for what it is worth about cyclist saying their cranks do not spin free or only 1 or 2 turns before they come to a stop, well I would say that is too much resistance based on my cranks spinning like a top but solid.

apollored

I had a spindle and bearing cups type of BB and have had it for 11 years but when it started getting water in and forming a rusty residue in the hub it only took 3 or 4 months to start knocking and feeling like it was rolling in the hub.

I have now replaced it with a cartridge type, hope it lasts as long as the old one did

wroomwroomoops

Thanks for reminding me that I don't want external BBs. I was kinda-sorta tempted, in order to tension the chain on an old vertical-dropouted frame (eccentric external BBs), but I think I'll continue putzing with chain tensioners.

FBinNY 

I'm definitely an old sq. taper dinosaur, and no fan of external BBs. But, if one allowed me to set up a single speed or IGH hub on vertical dropouts without adding an idler arm I'd consider that a fair trade off and would do it without hesitation.

wroomwroomoops

Philcentric

FBinNY 

That's one I had in mind when I posted. As I said, I prefer classic sq. taper BBs, but I'd take this over an idler arm any day.

wroomwroomoops

Here's the deal: I do like my vertically-dropouted frame and would love to convert it to a (more reliable) singlespeeder, but
price of 2 Philcentric cups + price of special tools for Philcentric installation + price of crankset compatible with Philcentric > new frame with horizontal dropouts