pel

Got a 2006 Cannondale Mountain Tandem in April 2006 for European tour.
Rear crankshaft bearing failed completely after 6000km.
Is this to be expected/normal??
Thanks

mrfish

On a single bike, low quality b/bs ridden as winter trainers without mudguards can easily fail at about this mileage. Failure is normally due to lack of lubrication (being washed out as the bike is washed / spray from the road) rather than stresses per se. Thus you should view the current sealed b/bs as a disposable wear items.

Whether the economics are in favour of buying cheap or expensive depends how many $ you assign to changing the worn one. For example (in GBP):
I normally need to replace the £10 bottom of the range campag b/b in my training bike every 2 years. Cost per year £5 plus 1 change.
Record b/b in my race bike lasted 6 years. Theoretically you could replace the bearings, but I just bought a new one.
Cost per year £8.5 plus 1/6 change
My Royce bottom bracket cost 2.5x the Record one, but is now 12 years old, has had bearings changed once and is still sweet as a nut. It will probably last for ever. Disadvantage is that it won't be very light compared with b/bs and cranks available in 2020.
Cost per year £10 so far plus 1/12 change

The other cause of early failure on b/bs is having a poorly faced frame - have a look when you take out the failed b/b. Surfaces that the b/b screws into need to be smooth, bare metal all at 90 degrees. If it's not get your local shop to run their facing tool over it.

ElRey

yep. normal.

stapfam

Had about the same milage when mine went. When it went- I wanted to fit a better quality Shimano BB in but due to the length- I couldn't. The quality as fitted was LX and in 118mm length, if I remember correctly. I could not get a 118 in XT so had to get the LX. By chance- I had an XT in 115 in my box for the Solo, and tried fitting it. It would fit. So I now have a 118 LX in the spares box and I am still running 118 on the front and the XT 115 on the rear. By adjusting the concentric off-centre, I still have the Crossover sprockets in line and the pilot has not realised that he is offset a fraction on his cranks. When I get round to it, I will fit an XT 115 on the front- some when.

zonatandem

Better quality sealed BB costs more to start but will be more cost efficient in the long run.
Had a Phil Wood BB get a bit loose after 30,000 miles. Phil replaced it, for free.
The other Phil lasted us 64,000 miles and still ran smoother than Campy when we sold that tandem.
Put 57,000 miles on 2 Syncross BB on another tandem, still working fine when we sold that tandem too.
Anybody can make something cheaper, but quality lasts . . .

pel

Thanks for your comments Mrfish, ElRey, Stapfam, Zonatandem.
Must admit I was disappointed at the Truvativ bearing failure at 6000km.

Will be following up on the one year warranty.
Regards

dubbelop

FWIW: in the cycling community, the ISIS system is also known as the CRISIS system

I do the maintenance for a set of spinning bikes; we managed to destroy the Truvativ ISIS bottom bracket on the instructor bike (used in eighteen 45-min. spin classes a week) after just over a year. I replaced it with a 4-bearing 'Downhill' model by Truvativ, hoping this will hold up longer. The simple Shimano square-axle models last over three years and then sometimes the axle ends break off, the bearings never seize.

The ISIS problems are caused by the big axle. This is nice for stiffness but since the bottom brackets shells are still the same size, the bearings had to become smaller to accomodate the axle. Nowadays you get all kinds of BBs with 'outboard' bearings; not only with ISIS BBs, but also on Shimano's Octalink models. That's a workaround which turned out to be necessary to overcome the problems with the smaller bearings.