Bottom Bracket Conversion Woes

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vintage '53

vintage '53

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Mar 25, 2012
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I am building a klunker replica of sorts from an old Colson frame. I jumped right in with both feet and bought the first american to euro bottom bracket adapter I found on Amazon. Well, it turns out that was a big mistake. With the old bearing cups removed, the shell on this frame is about 63mm wide. With the adapters installed, it's about 69mm across the flanges. Perfect, right? Nope. The faces of the adapters are recessed 2.5mm each, so actual distance between faces where the BB will install are 64mm apart. The Shimano BB-UN55 I bought won't tighten up at all. My initial solution is to make some spacers out of the flanges from the old bearing cups. Will take some machining, but i have access to the right machine tools at work. My concern here is that spacing out the adapters decreases their engagement into the BB shell, thus weakening the integrity of the whole unit. The last thing I want is a wobbly creaky crank. My other option is to purchase a different BB adapter. With more web searching, I've managed to find some which do not have recessed faces. Problem is, I can't reach through the computer screen and measure them before shelling out another $25. So I'll toss it out to the considerable wisdom on this forum. What advice do you guys have? Thanks
 
Use an old fashioned 1 piece forged crank & bottom bracket that falls right into place? :shock: :D
 
dougfisk said:
Use an old fashioned 1 piece forged crank & bottom bracket that falls right into place? :shock: :D
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I fight to stay away from 3-piece cranks, so this sounds like a winner. I wish 3 piece cranks could be adapted to 1-piece. But if you insist on going that route, it seems like many of the units for sale would have spacing and clearances listed. If not, you might try the website for the company that manufactures the part to get the info you need, then purchase it wherever it's cheapest.
 
You are not treading new territory here, and likely someone else on this forum has been there before and will direct you to a site that has the proper info and/or is willing to be conversant with you about your needs. BUT, you might try here: http://www.harriscyclery.com
Likely, too, is that you can sell that one you have to a member here and not be stuck with it on the shelf forever. In fact, I should go measure one of my frames and see if...............
And dont feel bad.......conversions (of all kinds) are often 'problematic'.
FWIW, since you can get/do the machining free, why not go for making the spacers and see if you can get this to work? If you do it well, I think there is a good chance it will be OK.
 
Thanks guys for your responses,

dougfisk said:
Use an old fashioned 1 piece forged crank & bottom bracket that falls right into place? :shock: :D
Click to expand...
Yeah, for a semi-panicked minute that was my thought too, but I'm commited to the three piece crank because it is really part of the klunker style and look I want to duplicate. Besides that, I'm using an internal gear rear hub with a chain line that would be difficult to match using a one piece crank.

ozzmonaut said:
I fight to stay away from 3-piece cranks, so this sounds like a winner. I wish 3 piece cranks could be adapted to 1-piece. But if you insist on going that route, it seems like many of the units for sale would have spacing and clearances listed. If not, you might try the website for the company that manufactures the part to get the info you need, then purchase it wherever it's cheapest.
Click to expand...
ozzmonaut - yours is my favorite username on this forum :) It seems to me that most of these adapters are products of China or Taiwan. I wish they did have concise inormation on their websites. Anyway, I did find one on eBay that looked promising and have a question in to the seller. We'll see if he can help. Right now that's looking to be the easiest way out.

gcrank1 said:
You are not treading new territory here, and likely someone else on this forum has been there before and will direct you to a site that has the proper info and/or is willing to be conversant with you about your needs. BUT, you might try here: http://www.harriscyclery.com
Click to expand...
That's a great site and the associated Sheldon Brown pages are my favorite web resource (well, this place ain't bad, either) for bike wrenching info.
 
Looks like I'm the only one responding to my own thread. :oops: That's OK, as I've been busy doing what I probably should have done in the first place before posting here. That is - scouring the web for all the info i can find regarding these bottom bracket adapters. And you know what? It ain't much :x None of the importer's sites have any useful dimension given for these things. Short of calling them and hoping the person i eventually get to talk to is knowledgeable, I think I'm going to have to go by photos alone. Here's what I originally bought off Amazon http://www.jbimporters.com/web/sear...+KITS&CatThreeId=BLACK+OPS&dfadfkawe45d9drh=3 Notice the recessed area where the BB is threaded. Here's what I think might work http://www.seattlebikesupply.com/catalog/bottom-brackets/bmx?page=2 This one has no recesses, so hopefully, when the width of the flange on the adapter is added to the shell on the bike, it will be wide enough to use a standard 68mm bottom bracket cartridge. There's a couple of guys selling these on eBay. I've got a question in to one of them now asking if he can measure the flange for me. I've got my fingers crossed. Will let everyone know how it goes. Cheers
 
how's this project coming along?

maybe i'm not thinking clearly this morning, but it seems to me that if the adapter spacing was only 5mm too narrow the cartridge would still tighten but the non drive side cup would just be protruding too much out that side, possibly affecting left crankarm installation...
 
FunkyStickman said:
I'm planning on doing a BB conversion as well, so I'm interested in what you find!

Sent from my GT-P1010 using Tapatalk 2
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i think there are several threads worth searching on this subject, i'll second the mrp unit- i have them in 3 prewar schwinns.

while most are flat and space out the shell to an effective 73mm (IF your bb shell is 68mm to start with), i have to say i like the look of the one in the j&b link. that recess would make for a low profile, clean looking install with a 68mm cartridge.

i'm still puzzled by the op...
 

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