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Old 03-22-08, 01:48 PM   #1
badmother
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Still struggeling. BB with cottered cranks.

Hope the small pix makes sence. Still struggeling, hope somebody can tell me what to do. Want to upgrade the Bb on this bike. Threadless BB housing, Diameter 38 or 40 (only know after remowing shells, do not want to do that unless I know a solution is present), 70 mm wide.

Hope to find some sort of solution to get rid of the old system and replace with a new system so I can put modern cranks & chainwheels. It is not possible that I am the first one to think about this? Plse help, want to ride soon!!
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Old 03-22-08, 02:25 PM   #2
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Badmother,
What make of bike is this?
Looks to me like one of the folders made in Poland and marketed as "Universal" or some other make.
If it is, then you have three problems, I'm afraid.
One is that the BB spindle is welded to the chainwheel, both steel of course.
Another is that the bearings and BB shell are oversize compared to most other makes.
The third is that the constuction of the frame is such that the end of the frame tubes protrude into the BB cavity. That is no problem with the bearings as supplied, but prohibits the fitting of a cartridge BB, even if you could get one of this size.
The left crank (also steel) is cottered so could be replaced with a cottered aluminium one.
So overall, not good news for you, unless someone has better ideas.
However, this BB is bombproof if you can live with the weight and the small chainwheel size, which gives rather low gearing.
I would be as pleased as you if someone has a solution to this problem.
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Old 03-22-08, 02:59 PM   #3
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Poland: Yes
Welded: No, cottered on both sides. Chainwheel and cranc welded together, but remowable from the spindle on both sides.
Owersized: Yes, approx 40 mm across (diameter).
Live with the weight: Would prefe not to.

The thing about "The end of the frame tubes protrude into the BB cavity." I do not understand, my English is not good enough, I am sure I`ll understand when I see it.. Could you explain, or maybe pix?

I wish somebodu would make a spindle for this type BB that had the square ends and threads on the spindle. Easy upgrade!

There is one option that my friend mentioned, but I am hoping for a more professional one. He said: remowe (angle grinder) the whole BB housing from an old bike with normal BB size and threads. Grind it down to smooth, and put innside existing BB housing. Have somebody weld it in place. Paint and put proper size modern cartridge innside. Could this work? Might want to eksperiment with gearing/ chainwheel sizes, so I relly want an upgrade!
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Old 03-22-08, 06:26 PM   #4
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Give me the outside measurement of the cotterd axle and the inside measurement on the spindle/axle and I will see if I have something at the shop.
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Old 03-23-08, 04:12 AM   #5
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If you have cotters both sides then there is another option, and that is to keep the cups, bearings etc., but machine squares on both ends of the BB spindle and tap the ends for retaining screws. Not an easy modification but may be better than some other options.
You could then fit modern square hole aluminium cranks with detachable chain wheel and choose your gear ratios by varying the chainwheel size.
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Old 03-23-08, 06:44 AM   #6
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Is a Thomson Bottom Bracket

Just serviced a freinds Roadster bike that had that.

I saw a racer with Alloy cranks on a Thomson BB, at the dump.
I found a Hacksaw blade and ripped the BB off the frame.
Took it home.
Then realised it didnt fit any bikes I had.

Geuss you could find cottered cranks to put on it.
As most bikes used to use them.
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Old 03-23-08, 08:03 AM   #7
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From the lead given by alecw35, I find that there is some useful information on
[URL="http://http://en.wikipedia.org/wiki/Bottom_bracket"]
This is a good starting point for anyone with bottom bracket compatibilty problems, as it has several links to other informative web sites.
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Old 03-23-08, 01:58 PM   #8
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Thank you for responding all of you. Not sure how to measure what Sixty Fiver is asking, my English is not good enough. Visited the wikipedia page and links earlyer today. Lots of info, but no solutions.

I think it is sooo strange that nobody made a easy solution for this! Somebody said there is a solution, but since he cannot tell me exactly, just that it should be possible to buy from most online stores, then I cannot use the info. Problem is most online shops do not tell you both mesurments, just how wide (68-70). Found one cartridge with no threading somebody said I could use, and I agree, but again they did not tell me all I need.

Sent e-mails to a few online stores, hope they answer me after easter.

Made a desicion what to do, need some few days to finish. Did alot of filing today (want to see my blisters?), need to take out the angle grinder, but must wait until after easter. Been looking for my Dremmel today, could not find it (so I made my first attempt on making a wheel from a 28 hole rim and 36 holehub instead. Turned out well, but need some shorter spokes).

I`ll post some pix of my solution in a few days, struggeling with some crappy laptops, cannot bring myself to finish repairing them, so pix is a problem at the moment.
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