View Full Version : Large O.D. Bottom Brackets and BB shells ( approx. 57 -59 mm)

10-27-2013, 08:00 PM
I'm sure you have all seen those large size Bottom Brackets (like on cheap dept. store bikes) I have a few on old bikes and would like to upgrade the cranks and bottom bracket parts - (so I could put higher quality chain rings and cranks - etc.) - I'm guessing the sizes - O.D. are approx. 57 -59 mm -one example : I built a street fox frame, the rear wheel section has a big open space where the crank parts were - I would like to set it up with new bottom bracket etc. (forgive my ignorance - but I have not yet spent time with a caliper to get the proper measurement) is there a 'Standard size' for these bottom bracket shells? Also this particular part (on my street fox frame) has no threads - just the open shell with raised ridges about a 1/4 inch in on both right and left sides - ------ - any Ideas?

10-27-2013, 08:22 PM
....not exactly clear from above what you're trying to do, but will guess. To convert a 1-piece oversize shell to smaller 3-piece shell, you can purchase a converter kit. I have one on my trike, and it's called 'DMR wondercups', there are other similar versions. Allows you to fit a standard threaded cartridge type BB, and seems a very neat and practical solution. Been running mine for several months now, with no issues..........

10-27-2013, 08:40 PM
It sounds like you have what they call a standard American one piece shell.
It usually has press in cups and bearing ring are held in with washers and nuts that are mounted to the one piece crank.
And Frank is correct in talking about a conversion unit that will press in and allow the use of a three piece crank unit.
Amazon and eBay are 2 sources and online bike shop as well as your local bike shop could be of assistance to get you the proper unit.
Harbor freight sells digital calipers pretty cheap if you care to really be able to read the number.
Like Frank not sure if you asking for designation or or if it can be converted.
So I hope this info is at least useful

10-27-2013, 09:26 PM
I found the 'DMR wondercups' - that could be a solution (especially if I don't have to do any welding.) I could slide in a 68 or 73 mm shell inside with lots of extra room - so is this kit all that all I need to take up the extra space?

10-27-2013, 09:27 PM
Also I thought you might be interested in this very cool trikes gallery page I found recently http://www.pinterest.com/wonkybent/recumbent-trikes/ (http://www.pinterest.com/wonkybent/recumbent-trikes/)

10-28-2013, 12:54 AM
"It sounds like you have what they call a standard American one piece shell" it looks like this one : http://chopzone.com/hacking3.html so the conversion unit might be the way to go - I'll have to do more research - thanks again for you help - much appreciated - Paul

10-28-2013, 03:36 AM
...the kit is all you need, don't have to 'slide in a 68 or 73 mm shell inside', or any such. With your 1-piece crank BB shell, tap out the bearing races each side, then tap in the Wondercups. They are held in place with 3 long bolts, as supplied, and have to be aligned correctly to do the bolts up, but easy to do. All you do then is screw in a new cartridge BB to your liking, and it's done. You must choose the correct spindle length for the new BB, to get correct chain alignment. The Wondercups will only work on a 68mm wide shell, which is almost certainly what the American 1-piece crank shells are. Only other thing is, the threads are different on each side of a screw in, 3-piece crank BB. Left side is a right handed thread, right side is left handed thread - opposite way to how the pedals screw in each side....if that makes sense......

10-29-2013, 02:00 AM
I finally dug my caliper out of my tool box - the inside diameter is 45 mm or 1 and 3/4 inches (1.77165) is that a standard size for the wonder cups BMX to MB conversion kit? (I could not find that size on google) I guess I need to check a bike shop - or if you know the answer let me know. Thanks, PaulPb

10-29-2013, 09:10 AM
Paul, where you located?

It will most likely be cheaper to buy a new BB shell and have something that is better quality as well as having a standard size.

If you are using mild steel, then you can get them directly from AZ: Steel Bottom Bracket Shell (http://www.atomiczombie.com/BBRAC%20Steel%20Bottom%20Bracket.aspx)

If you are in the US and using Chromoly or Aluminum you can get them Nova Cycleworks (http://www.cycle-frames.com/bicycle-frame-tubing/STEEL-LUGLESS-SHELLS/) or Paragon Machine Works (http://www.paragonmachineworks.com/cgi-bin/commerce.cgi?search=action&category=0001)

Note at Nova and Paragon, "Steel" BB's are 4130 Chromoly.


10-29-2013, 12:05 PM
I'd rather not disclose my location - I have purchased from nova cycles - they fit with the bottom brackets I have used in past projects or have recently purchased - so that does work for me - It's just those large type - standard American one piece shell - you commonly find on 'donor bikes' (especially the tail end) - it would be nice to find what parts will fit instead extra hacking.......

10-29-2013, 01:03 PM
We are not asking you to put your address just city and/or state is helpful... or you may find that people just give up trying to refer you to helpful sources simply because it becomes to much effort to guess what sources would help you get past your problems...

And the bottom bracket you refer to may be common on dept store bikes, but it is not a standard size.


11-01-2013, 06:36 PM
Hi to all
Here in Oz, the bottom bracket you describe is called a US Oversized or US OS.
Just done a search on EBay for "bottom bracket conversion" and come up with all sorts of goodies.
Hope it helps.

11-01-2013, 07:57 PM
....the internal diameter of US one-piece BB shell is 51.3mm, or 2.02 inches. This is contrary to the measurement you gave earlier? Is your caliper zeroed in correctly? TruVativ is another manufacturer of the conversion kit.......