So I shot the bearings in my sealed BB.

And me being me, the only thing I'm going to do here is replace it. But I've never really shopped for BB's before (I just tell shops, that one please, and let them resolve chain line issues) so I have no idea what is good and there appears to be so much choice.

I've taken a load of measurements of my existing shot BB and these are the details I can deduce:
73mm BB Shell on the frame
45mm Chainline
145mm 8 spline (ISIS?) axle
ISIS BB installed (20 spline tool needed, Shimano one?)

So that gives me a shopping list that suggests:
73mm x 145mm ISIS BB.

Simple I thought... but I can't find any 145mm axles on the ISIS BB's I'm finding online.

Am I doing this wrong? Wrong measurement somewhere? Axle is measured tip to tip.

isis (raceface fsa truvative) is not the same as shimano splined.
if you can get the bb out it should say what it is. if the cranks are shimano it will be shimano bb.
if fsa etc it will be isis

145mm is massive? it's usually 113-118 for mtb's i presume road will be narrower. as it's a bmx try alansBMX and see what bb's they list

The cranks are Profile.

I thought the axle was massive too, so I measured it twice in case I was a dunce. 145mm for real.

I'm going to buy a Shimano BB tool and get the BB out so I can figure out what the story is.

ah profile cranks are totally different they have an axle and press in bearings. check the profile racing website

Was thinking ISIS didnt make sense as soon as I read profile.

You only get ISIS on Euro mtb style bottom brackets, used on race bmx's

Your dont need to change the spindle on 3pc US BB cranks. Infact, These type of spindles are very rarely labelled by size, just by brand. and diameter.

You just change over the cratridge bearings, which very simple to remove. Just get a hammer & screwdriver and punch them out. You dont even have to be careful as you are binning them.

Replacement bearings are very good value and last a very long time, available from any BMX shop and sold by the size of the hole. (19mm, 22mm etc)

Thanks.

Helped a lot.

Got the BB out, found it has 6804RS 20x32x7 bearings.

Now if I can just find a ceramic supplier of these.

These would be fine wouldn't they?
http://www.vxb.com/page/bearings/PROD/Kit7669

that's a joke isn't it VB? profile cranks probably weigh twice as much as a pair of heavy road cranks. for the cost of a pair of ceramic bearings you could get several sets of enduro (the ones with blue seals that are in my profile hubs) or SKF plus the tools to fit them properly.
or are you racing at national level and need the freest running set up ever? even then i would rather have stainless bearings because of the stress put on them by dodgy landings.

if you want a seriously light bmx without compromise then pm me as i know the owner of dialled bikes/relentless bmx team and he may have some of his titanium BMX race frames left

Oh I've already got a frame, lovely wheels and the whole thing from Rob just last year. It's lovely.

All that's happened is I've shot the bearings. I'd like to replace them with something that is free running, silent and is unlikely to need me to service them for the life of the bike. In my mind that last part means it's OK to spend money on decent ceramic bearings. And there's little point of putting ceramics in steel casings as then the weak link is the casing. So might as well make sure I've got the ceramic casing too.

Am I just doing this all wrong? I think those ones are the right size, and whilst they're not as cheap as a steel set, a steel set is precisely what I'm taking out because I've shot them. Surely ceramics would last a hell of a lot longer and possibly never be shot?

How long have the bearings lasted? What's your objection to steel? How many more years will the frame last?
Replace steel balls when they need replacing, lubricate regularly and your steel BB cups will probably outlive the frame.

No idea. That I've had to replace them at all. No idea, depends whether I hit a bus.

I went for the hybrid ceramic bearings from Enduro. They're not quite as offensive as the full ceramic ones. Should be here before the end of the week.

if they are the same ones on it from when you bought it, they ain't profile.

the chainring was, IIRC.

I don't know if you can put profile crank arms on that BB, you may have to change the whole lot.

looks like you've sorted the problem anyway.

and ceramic bearings!

nutter

Damn, I knew I should've gone for the ceramic casings too!