kromar

hi, i have a bike that i used for a long time and now started to replace some parts to revive it:O

now i have removed the BB and i looked a bit around if i can find the same, but local bike shops dont have the exact same BB anymore.
so when im looking for a new one, how can i tell if it fits in my frame and the pedals will fit on it?
is there a page where i can see all the measurements of new BB's?

its a BB-UN51

Ex Pres 

Those BB-UNs are still available, I think the latest is BB-UN54 (and the -26 is a less expensive version, too).
You can also find Tange models and one labeled BB-7420 (IIRC) that are basically the same.
They are all JIS taper, so no worries there.
All you need to do is make sure the threading is the same (more than likely English 1.37" but I can't tell from the pic)
And the spindle length end to end needs to match up - they run from 107mm to 125mm ~3mm increments.

And your local shops should have been able to help you out. This is a pretty simple request.

Edit - and keep that metal cup from the left side. Newer ones are plastic.

fietsbob

You measure the over all length, in MM.
.

you ask them to get one from their distribuitors, in the Summer there are weekly shipments to refill stock, bring it in , and they will measure the length needed..

are you wanting to change the whole crankset? but are asking
just about the Bearing assembly in the center?
the pedal question makes me think you seek the whole thing..

wrk101

+1 While many shops do not stock a lot of BBs, they can get them in a couple of days. Or you can buy one on line. I use a fair number of the UN26 BBs, they are heavier than the UN54, but only cost about $10 each on line ($20 each at my local bike shop).

kromar

thanks for the quick answers yes the threading is BC 1.37x24.
will a BB-UN54 have the same spindle length or do they come with different lengths?

ok so i probably should look for a other LBS since they could not even handle such a simple thing
well i have a bit a limited vocabulary when it comes to bike parts at the moment but im learning fast^^ i dont think i nee to replace the whole crankset but only the gears (probalby the wrong word again). the question was more if its nor possible to get a BB with the same square fitting that i need to replace the whole thing anyway.

kromar

so i can order a BB-UN26 and just need to know the width of the whole thing so i get the correct one?

kromar

thanks a lot for all answers. i googeled a bit for pictures of the UN26 and UN54 BB and with the stickers on it it became pretty clear what i need

so i need a UN26/54 68 107mm

Ex Pres 

The gears on the crankset are called chainrings. You'll need to know your BCD (Bolt Circle Diameter) to be able to replace those. Most of the time this is not an issue, but there are some obsolete BCDs out there. If you have a 118mm BCD (some older Japanese cranks - SR, Sakae), then it becomes tougher to find.

kromar

thanks again for the information chainrings, good to know how its called i guess i will have to measure some of the parts before i can order new ones:O i will definitely come back with more questions if i progress with the bike.

EDIT: the crankset is a about 15 year old Shimano LX version with 5 bolts. any idea how difficult it will be to get new chainrings for that thing?

wrk101

Very easy to find chain rings. But buying them individually can be costly, versus buying a complete crankset. It takes a lot of riding to wear them out, so unless they are really worn out, I would just keep them. What does tend to wear out quite a bit sooner are the chain and rear cassette or freewheel. They are not the same.

You will need to know whether you have a freewheel or cassette, the number of speeds, and the size of the cogs. Chains are sized for the same number of rear speeds, so you are going to need that information anyway.

BBs are sold to match the crankset, so if you go with a replacement crankset, you need to get the right bb to match it.

I rehab a lot of bikes, I rarely need to replace chain rings (less than 1% of the time), but I often have to replace rear cassettes and chains (maybe 50% of the time for chains, 25% of the time for cassettes). I am replacing a crankset right now, not due to wear, but due to cosmetics (it looks like crap, and its on a really nice bike, so it has to go).

kromar

i would say the chainrings are pretty worn out, but i will go ask the LBS and see what they think about it:d i already ordered a new rear cassette for the new wheels and will get a new chain as well.