I want to update my '57 Holdsworth Cyclone's cottered BB.

The catalogue at the time describes the bike as having a 'Continental' BB. Are there modern BB's that will fit? What spec?

Probably a standard British bottom bracket. Spindle length will be according to the crankset you choose to put on it.
What is the current cottered chainset that it has now? And why replace it?
Phil

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if frame constructed with a British manufactured shell there is a possibility you may find it to be slightly underwidth, ~66.5mm rather than the nominal 68mm

with such shells it is often helpful to place a one mm spacer behind fixed cup to achieve an ideal chainline, assuming frame in good alignment to begin with...

let readers know if you wish to stay with a cottered chainset or wish to change to cotterless so that their suggestions may be more on target

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Good question...

I can't get the cranks to line up with each other. I replaced the cotter pins (old ones were stripped) so I could be that. Or just that I haven't seated them properly. But it did make me think, why not just replace the BB and make things lighter to boot. If the bike was in great condition and all original, I'd want to keep it original. But it isn't.

Good point. I'd want to go cotterless.

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crank cotters -

one needs to make sure to have them the same way round on both sides, either head leads in the rotation or tail leads

if mixing one new and one used pin the registration often comes out slightly off

if you examine the pins one will appear to have a lighter cut than the other

a few strokes of a file on the pin with the lighter cut should sort things

t'is easier to get good registration from the outset if one replaces both pins with new & matching ones at the same time


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Do you have a cotter pin press? It is necessary to get cotters in with enough force that they don't loosen up. What is the current cottered chainset on the bike? I'm on a mission to bring cotters back!

Phil

I am guessing that a "Continental" BB is 68mm wide, but that's pretty easy to verify. Unlikely, but I suppose it might also mean 35 x 1 metric threading, either anticlockwise fixed cup (Swiss) or clockwise on both sides (French). I am hoping it means ISO 1.375" x 24 TPI, 68mm width. As mentioned by others, a substandard BB shell width is the easiest of these problems to address.

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a simple C-clamp be adequate to generate plenty of seating pressure

can be employed for removal as well

care must be taken to check that all is in alignment prior to beginning to apply pressure...



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very much doubt Holdsworth would use a metric BB shell in '57, neither Swiss or FR. If you want to keep things "in the family" I'd suggest a Campagnolo crankset since Holdsworth was the UK importer for many years (in the family but maybe not period- or model-correct)

The steel Campy Sport square taper would be roughly period correct. And it's so shiny!
Phil

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most folks are somewhat surprised at the actual launch date for the Sport model chainset

t'is about fourteen year later than subject frame

first catalogue appearance occurs in the Nr.16 catalogue supplement of November 1971 -




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I always thought it was a decade earlier than that! Thanks!
Constantly learning more arcana, and glad for it!
Phil