Cycling UK Forum

Am I really unlucky as I am now about to have my 4th bottom bracket fitted on my MTB (square taper cartridge) in just over 3000k from new.
About half of this distance is on dry rough rocky tracks with lots of potholes, and I usually ride over some of these potholes by standing on the pedals to ease the shock in the saddle I am only 78kg so am not over heavy.
Is this normal as they are quiet cheap to replace ?.
Rob

That's waaaay too many.

What's the cause of failure? Same every time? And what sort of bottom brackets are you using? I'd probably expect to get at least 15,000 km (and hopefully more) out of a Shimano un55.

Are you fitting them yourself? Poor fitting or knackered threads inside the BB shell creating increased wear on the bearings is my first thought. Might be worth having the LBS run a tap through to check the threads.

Should last longer unless you are subjecting to pressure washing or similar.
A cheap BB might not last but generally Shimano mid-range (UN54/55 series) can last years.

1st two had side to side movement of the crank arms, this one is making a knocking noise under pressure.
All have been Shimano makes, I don't know the model numbers, fitted by my LBS, no pressure washer used and not over washed around the bottom bracket and wheel seals.
The third one he replaced for free as the second only lasted 300km, I cannot figure it out.
Rob

You really need to find out which model of BB is being fitted?

I'm as bemused as the OP
I get 20,000miles+ out of a Shimano UN55 BB.

Are you sure that the BB needed replacing or just tightening? I have had it that I've needed to tighten the shells

I have never replaced a bottom bracket. Never. In a lifetime of cycling, and many thousands of miles on my oldest bicycle.

I did clean and re-grease one on a late 60s Dawes last year.

I'd be concerned that they are not being installed correctly.

Going to take it in tomorrow to get it checked, i'm wondering whether the very dry dusty tracks are to blame rather than water?
Rob

Antan1 wrote:Going to take it in tomorrow to get it checked, i'm wondering whether the very dry dusty tracks are to blame rather than water?
Rob

IME,decent quality Shimano UN53/5/6,etc BB's are very well sealed against dust,muck and wet,so I don't think its that.
There's something definitely amiss somewhere but it ain't the weather

Edited for typo's

Vorpal wrote:I have never replaced a bottom bracket. Never. In a lifetime of cycling, and many thousands of miles on my oldest bicycle.

I did clean and re-grease one on a late 60s Dawes last year.

I'd be concerned that they are not being installed correctly.

Ah - are you talking about a 'proper' bottom bracket - one where the axle, cups, balls and lockring come separately and you clean it, grease it, set it, adjust it and tighten yourself - very satisfying and they give you much higher mileage than the current cartridge bottom brackets which you just put into your bottom bracket shell, centre it and tighten up.

The 'proper' ones used to give me 30,000 - 40,000 miles depending upon the quality and whether they'd been subject to wet conditions. The cartridge bottom brackets give me about 10,000 miles - but I don't buy the cheapo ones.

To have never had to replace a bottom bracket, even a decent 'proper' one in a lifetime is very unusual - and very lucky. Mind you - how long is your lifetime? - and how many miles do you ride each year? You must have a very smooth action.

I would suggest that having to replace even a cheap BB at the frequency that Antan is doing could indicate something wrong with the BB shell in the frame - are the threads misaligned perhaps - or is the shell itself deformed? Nothing lasts forever, but this is really extreme.

JohnW wrote:..............The cartridge bottom brackets give me about 10,000 miles - but I don't buy the cheapo ones...........

What type/make of BB do you use?

if they are BB-LPxx units then they are the heaviest, cheapest shimano BB units. These units have the interesting feature that most of them are in fact adjustable; but no-one seems to have the right tools or indeed even knows that this is the case.

IIRC you need something like a deep full hex socket (~22mm spark plug hex size?) and there is a locknut (left threaded) and a tab washer inside. All this lot is underneath the LH seal.

LPxx units quite often wear out prematurely (adjusted too tight) or go loose ( need adjusting or worn from water ingress). But even if adjusted and lubricated correctly they don't last that well.

The better quality ( 10000 to 20000 mile life expectancy) BB-UNxx units are not adjustable. Dry conditions are not known for shortening the life of such BB units.

Are you sure that the units fitted are not 'shimano compatible' units which are not the same thing at all as 'shimano units'?

To have four BB-UNxx units to genuinely fail in that time would be unprecendented; the most likely explanation would be that there is a problem with the installation. I would ask to see the old BB units or at least ask if the centre bearing unit had play in it.

cheers

JohnW wrote:Ah - are you talking about a 'proper' bottom bracket - one where the axle, cups, balls and lockring come separately and you clean it, grease it, set it, adjust it and tighten yourself - very satisfying and they give you much higher mileage than the current cartridge bottom brackets which you just put into your bottom bracket shell, centre it and tighten up.

The 'proper' ones used to give me 30,000 - 40,000 miles depending upon the quality and whether they'd been subject to wet conditions. The cartridge bottom brackets give me about 10,000 miles - but I don't buy the cheapo ones.

Yes, I'm talking about the sort with axle, cups & ball bearings.

JohnW wrote:To have never had to replace a bottom bracket, even a decent 'proper' one in a lifetime is very unusual - and very lucky. Mind you - how long is your lifetime? - and how many miles do you ride each year? You must have a very smooth action.

I have been cycling for a bit over 40 years. When I was younger, my bikes were modified, changed and/or maintained often enough that I probably never gave my bottom brackets a chance to wear out. My oldest current bike is an early 90s Raleigh hybrid. I have no idea how many miles it has on it; I've gone through a few drive trains and two sets of wheels on it. It has been used for commuting & touring, but is currently used mainly for utility & winter riding. It is becoming in need of replacing or rebuilding, but I've never touched the bottom bracket or headset on it. My next most high mileage bike is a Claud Butler Paris that has ~10000 miles on it. I've only replaced normal wear items on that bike. I also have a childback tandem, which I've had for about 4 years. I don't think it had huge mileage when I got it; most parts appeared to be original. I suppose we've done a couple thousand miles on the tandem. My annual mileage varies quite a lot. 2012 Was my highest mileage year since having children, and I guess that was around 4500 miles.

JohnW wrote:I would suggest that having to replace even a cheap BB at the frequency that Antan is doing could indicate something wrong with the BB shell in the frame - are the threads misaligned perhaps - or is the shell itself deformed? Nothing lasts forever, but this is really extreme.

Yes, maybe my experience is at the other extreme, but it seems that more is wrong than just the BB; it could be a problem with the shell or frame.

shimano square taper bb only lasted 500-1000 km on both my wife's and my early mtb's. went through a few before going to outboard crank/bb set.

we do ride in all conditions and through deep mud and puddles though.

the outboard bb now last 1500-2000km .

square taper on our road bikes last for much longer. as do chain, chain rings, cassettes etc.