Changing Bottom Bracket & crankset from cottered to Sq Taper on 70's Gitane Tandem

Hello & help!

I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.

Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?

Thanks in advance, alan

al77 wrote:

Hello & help!

I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.

Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?

Thanks in advance, alan

It's almost certainly French, and as Sheldon Brown says, at
http://sheldonbrown.com/velos.html
"French-thread bottom brackets, like Italian, use regular right
threading on both sides. This means that the fixed cup will have a
tendency to loosen up in use. "

It's even possible that the drive side, or "fixed" cup is left-threaded
like ISO bikes, rather than the usual right thread on most French BBs.

http://www.yellowjersey.org/bart.html shows some heroics in reviving
another tandem with BB threading challenges.

Rethreading would probably involve first filling the existing threads
with brass and Andy Muzi is one person here who knows about that.

Your planned drivetrain modifications will result in much higher loads
at the rear BB so a high quality item here is in order. Have you looked
into getting a Phil Wood unit made in your threading? Costly, but it's
top drawer stuff.

If you want to do this on the cheap, then you may as well bite the
bullet and have it rethreaded to English, which affords a wide choice in
available BBs.

Ted

--
Ted Bennett

al77 wrote:
I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.

Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?

Your frame is threaded m35 x 1 (French). You may be able to use the
existing cups with a new spindle if they are in good shape. Check that.

Loose-ball French BB sets or Phil Wood cartridge systems are readily
available but an inexpensive cartridge unit won't be found in 35mm thread.

Modifying the frame for either a larger Italian 36mm thread or, more
extensively, filling then cutting 34.8mm BSC threads, can become a much
larger project (machine charges, paint work, shipping expense).

Italian cartridge BBs are available, but BSC are far more prevalent.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"Ted Bennett" wrote in message
...
al77 wrote:

Hello & help!

I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.

Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?


It is almost certainly French threaded, but no need to rethread. Replace
the cottered BB spindle with a square taper model. Keep the existing cups.
Check the dimensions between the bearing races on the old spindle. Then get
a new square taper spindle with the same race dimensions, and the overall
length and offset that you need to match the new crankset.

On 8 Sep, 22:14, "Dave Mayer" wrote:
"Ted Bennett" wrote in message

...



al77 wrote:

Hello & help!

I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.

Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?

It is almost certainly French threaded, but no need to rethread. Replace
the cottered BB spindle with a square taper model. Keep the existing cups.
Check the dimensions between the bearing races on the old spindle. Then get
a new square taper spindle with the same race dimensions, and the overall
length and offset that you need to match the new crankset.

Wow, thanks for the quick responses everyone!

It handn't occured to me that I don't need to change the whole BB,
just the spindle. I'll look in to that first of all. Maybe if I used
a triple crankset on the drive side I could use the 2 inner rings as a
double for the rear chain & the outer ring for the sync chain?

al77 wrote:
On 8 Sep, 22:14, "Dave Mayer" wrote:
"Ted Bennett" wrote in message

...



al77 wrote:
Hello & help!
I'd like to change the BB on our 70's Gitane tandem to square taper if
possible & economical to do so. It is fitted with a the original
cottered crankset & BB at the moment, with both the main chain & the
sync chain running on the same drive side. Ideally I'd like to fit a
square taper BB & get a new crankset so the sync chain can go on the
non-drive side giving me room to add a front mech for a double
chainset on the drive side.
Does anyone know if these 70's Gitane tandems have english threaded
BB's, or will it be French? And if it is French, can it be rethreaded
to English or Italian?
It is almost certainly French threaded, but no need to rethread. Replace
the cottered BB spindle with a square taper model. Keep the existing cups.
Check the dimensions between the bearing races on the old spindle. Then get
a new square taper spindle with the same race dimensions, and the overall
length and offset that you need to match the new crankset.

Wow, thanks for the quick responses everyone!

It handn't occured to me that I don't need to change the whole BB,
just the spindle. I'll look in to that first of all. Maybe if I used
a triple crankset on the drive side I could use the 2 inner rings as a
double for the rear chain & the outer ring for the sync chain?

I think you'll need to space the sync chainring farther away from the
other two than normal triple spacing, or the chains will snag each
other. ISTR the setup you describe being used on some tandems, though,
but with the small inner chainring being the sync chainring. Good luck,

Mark J.

If you can utilize an older Shimano UN-72 bottom bracket (or a modern
campagnolo square-taper cartridge BB), then you might consider just
buying the french retaining rings from Phil Wood, and then use any
cartridge bottom bracket where both cups are removable.

I have heard that the IRD/tange $20 bottom bracket can be made to
work, although it may require some filing as the cartridge diameter is
different than the Phil Wood diameter.

- Don Gillies
San Diego, CA