Bike Forums - View Single Post - Removing French BB fixed cup

06-29-21, 08:58 AM

#74

gugie

Bike Butcher of Portland

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Quote:

Originally Posted by bulgie

I have tapped English (and French) to Ital, but only by reaming first.
Mark B.

Quote:

Originally Posted by Charles Wahl

With respect: how does this even work? There's only about 1.25 mm difference in the thread (cup) diameter in theory, and Sutherland's says only 1 mm (34.8 vs 35.8), plus the two threads can't "nest" on the drive side because they're in opposite directions. Is this one of those ShelBroCo April Fool's products? I drew this up in CAD, using 1/24" as the thread pitch, and 60 degree (yeah, English is 55 degree or so), and when offsetting the "English" by half a mm, I get overlap between the two thread profiles:

Quote:

Originally Posted by JohnDThompson

It's best to ream first; forcing an Italian thread tap would be difficult. Bicycle Research used to offer a reamer/tap set for this purpose. I've used it several times with good success.

Good knowledge. Charles, since Mark and John have probably forgotten more about bottom bracket tapping then the two of us will ever know, I'll believe them. After retapping, the threads "looked" good, so I'll probably just install an English BB and give it a go. There's little downside, if it loosens on it's own, I'll go with my backup plan(s).

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