Bottom bracket query

[steveoo]

How long should a bottom bracket last.?
I've just upgraded my chainset and bottom bracket and found that the bracket was shot. Bearings well worn and grinding with little lubricant and water in there. It's only 8 months old and done approx 3000 miles on and off road

 

[Rohloff_Brompton_Rider]

Depends, I once had a bb last less than 50 miles, the gritty water had gotten into it. But I've had the same brand and model last for 10,000 miles.

 

[PpPete]

External bearings (like HT2) may be less durable than cartridge BBs. I've also heard less than wonderful things about BB30.

A couple of years ago I dis-assembled an old style loose ball BB that I'd previously serviced about 30 years previously. The grease had turned to soap and it was a bit "stiff" to turn. No "grinding" though and a thorough clean-out and re-grease restored it to "as-new" without even changing the bearings !

Progress?

 

[Cubist]

As bfb says, they can die in a couple of rides or last for aeons. The trick is to avoid water ingress, and to make sure they are well greased to start with. Standard HT2 tend to be relatively short lived, and although some would say you can regrease the bearings, the seals are very easily damaged and don't go back on properly, so very limited lifespan. I always make sure there is a thick layer of grease around the seals and never, ever get any water under pressure anywhere near them.

However, according to those in the know, the biggest killer of HT2 bearings is lateral load through ham-fisted fitting of cranks and especially overtightening of the preload plastic insert. (That's all well and good, but I remember one SLX crank that had to be drifted through the bearings with a lump hammer it was such a tight fit. )

You need to make sure the preload cap is only on enough to take the play off the cranks. If it shows any resistance whatsoever it's too tight and the crank needs slackening off and starting again. On a well used crank that can mean no more than finger tight on the star shaped tool.

 

[GrumpyGregry]

Bottom brackets last until they fail. The time that takes varies dramatically with use, precision of fitting, rider style, et cetera.

 

[steveoo]

Surely bottom brackets are designed to take a fair amount of stick especially off roading.???

 

[GrumpyGregry]

Surely bottom brackets are designed to take a fair amount of stick especially off roading.???

bottom brackets can be designed to do that certainly. Those made by that nice Mr Christopher King for instance. The others seem have this funny obsolescence thing built in with a touch of fail added on assembly which is a nice revenue stream for their manufacturers.

Even an XTR square taper sealed cartridge precision fitted by the finest wrench monkey money can buy will fail eventually.

All things decay. Entropy always wins.

 

[Cubist]

^^^^So much so that I keep a spare one in my toolbox. I can't justify a CK or even a Hope (unless someone can do some fast talking and show Santa where the bargains are hiding..) but I snap up the upgrade cast-offs when I see them. Last one was brand new, not even fitted for £11.