Re-threading a bottom bracket?

[hockeybike]

I'm building up a frame for a friend and stumbled upon an 853 schwinn peloton. After talking with the seller, he said he "re-threaded the bb" so that it would go from english to italian threading. Does this make any sense? He says he's worked in a shop and had access to all the tools, but I don't understand how or why you would do this, especially to go from english to italian...

[oliver1850]

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[old_fat_and_slow]

How is it possible to rethread the left side of the bb shell from Italian to English? They're threaded in completely opposite directions aren't they. Isn't that the big selling point of English threads, is that it reduces the chances of the bb coming loose while riding?

If some dude has cut threads in completely the opposite direction from how they were cut originally. I wouldn't touch that frame with a ten-foot pole. When torque is applied to threaded part, tremendous shear stresses develop in the threaded portions of both the male and female components. If dude has cut threads in opposite direction, I doubt the resulting threads have the appropriate thread height and depth to withstand the shear stresses needed to apply sufficient torque to keep the bb tight.

Course you could always install one o' these if the BB shell threads are FUBAR'ed, if you're open to runnin' a square taper bb.

http://store.velo-orange.com/index.php/components/bottom-brackets/grand-cru-threadless-bottom-brackets.html

Just my $0.02, and worth every penny I tell yah.

[ultraman6970]

Yes you can do that, but you need the tools to do it tho. And I bet probably 1% of the shops around your area have done it and might have the italian taps also. To do it you need an adjustable tap, then you go little by little.

By own experience the fix works fine, nothing wrong with the bike, for the guys wondering about the difference between 68 and 70 because italian bbs use 70 mm shells, the BB wont notice the difference, thats why u have a fixed and an adjustable cup.

Second option, put some brass inside of the bb bad threads and rethread it again, in that way you dont need to deal with italian taps, the bad part is that the shell area needs to be repainted. This can be done in aluminum frames also, actually should be easier because the stick used for it uses way less temp than with bronze.

Good luck.

[oliver1850]

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[old_fat_and_slow]

Second option, put some brass inside of the bb bad threads and rethread it again, in that way you dont need to deal with italian taps, the bad part is that the shell area needs to be repainted. This can be done in aluminum frames also, actually should be easier because the stick used for it uses way less temp than with bronze.

Good luck.

Not sure I'd go that route either. Brass doesn't have near the shear strength that steel does. (Will tend to strip the threads at much lower torque than steel.)

[old_fat_and_slow]

It works because Italian is a larger diameter. Most if not all of the original English thread is removed. The shell should be reamed to size before rethreading.



Ahhh, got it. You're correct then, it will work.

[hockeybike]

Thanks for all the input--as always, this place contains a wealth of information. I hadn't considered the shell spacing issue and since it's a bike for a friend who isn't particularly mechanically inclined, I think I'll pass on the frame.

[oliver1850]

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