Tandem bracket shell compatibility

[peetee]

I had the (hairbrained) notion that I could build up my Jack Taylor tandem frame for some friends so they could do some time-trials on it. I thought I could collate enough parts to do the job but have come across the daddy of all roadblocks. The rear bottom bracket shell is the Charter Lea pattern, somewhat larger diameter than standard (approx 4mm) and with a width of 74.5mm.
Does anyone know of a solution that will allow me to fit a square taper crankset? I have offered up a Shimano axle but the diameter is just a shade too large to fit through the cup apertures. It would be fairly straightforward to enlarge them but the Shimano axle may prove to be too narrow between the bearing races (68mm standard vs 74.5mm) and I don’t want to wreck a perfectly good Charter Lea assembly that might be worth its weight in gold for another classic tandem owner.

[iandusud]

Some interesting and possibly helpful info here https://www.classiclightweights.co.uk/c ... nd-others/

[rjb]

There might be some info in this recent thread. viewtopic.php?f=5&t=147648&p=1635320&hi ... r#p1635320
How did mercian man get on with his investigations, hes not posted back since.

[peetee]

Thanks. Some info to mull over. I have managed to get the Shimano axle in to the cups but two problems remain:
1) the oversized cups are milled for 5/16 bearings, the shimano axle 1/4 bearings.
2) the adjustable cup is set in with no room for a lock ring (5/16 balls fitted)

Probably a stupid question, and not something I’d ever try on anyone else’s bike, but is it feasible to run 1/4 bearings on a 5/16 cup face? Obviously there is a considerable difference in mating curvature but I would guess the ring of balls would run wide too?

[Ugly]

Are you a Tandem Club member? Their technical officer might be able to help you.

[peetee]

Thanks. Will look in to that.

[pq]

I wouldn't be surprised if Cliff at Royce could do something, but it wouldn't be cheap.

[531colin]

Maybe something like this could be pressed into service? (provided the flanges are big enough?)
https://spacycles.co.uk/m16b0s110p2620/ ... om-Bracket
It will obviously sit "further in" in the bigger diameter BB shell, you should be able to get the chainline right with reference to Brucey's "stickout" list?

[rjb]

would that spa bottom bracket work in an old raleigh which had a wider bottom bracket. Sheldon suggests they vary between 73 and 76 mm width. i suppose it may depend on how much thread is available on the yst unit and whether it could cope with having fewer threads to engage it.

[slowster]

Does anyone know of a solution that will allow me to fit a square taper crankset?

Do you still have all the various parts to build it up with a cottered crank? If so, why not use them?

[emleyman]

Would a solution like this one for fitting a modern square taper into a 75mm Raleigh shell work?

https://bicyclehub.co.uk/mk3-sealed-bottom-bracket

I've never tried it, but it looks like a good way of getting around Raleigh 'standards'. It might work for your Chater Lea as well.

[9494arnold]

I used to be in the Tandem Club, I am sure they used to have parts to sleeve down Chater Oversize Brackets . Mind you that was about 30 years ago, when I had a short wheelbase Claud Butler twicer .
I made my own cross over Drive chainset out of cottered chainsets and judicially filed cotter pins . What a faff.
You can buy cotterless bottom bracket assemblies intended for frames with damaged threads, they screw into themselves . One of those on it's own might help (not sure how wide the ends are) , failing that an enterprising machine shop ought to be able to do the business in filling the gap .

[peetee]

Does anyone know of a solution that will allow me to fit a square taper crankset?

Do you still have all the various parts to build it up with a cottered crank? If so, why not use them?

The plan is to use Campagnolo record square taper cranksets non-crossover using the inner ring as the link drive and the outer as the final drive to the cassette.