I am restoring a 1980s Zeus and after much research, purchased a NOS French-threaded Zeus BB off good-old EBay. And it doesn't fit! The cups won't even start, I.e the cups are larger than the shell.

Further investigation suggested the shell is probably British standard (or ISO if you prefer). So I did what any normal person would do BEFORE parting with their cash and tried a Shimano hollowtech cup I had lying around in the garage...and it fitted perfectly! Lesson learned.

The problem I have now is because my Zeus shell is right-hand threaded on both sides, I can't simply purchase ISO cups because one will be left-hand and the other right hand.

Unless I am missing something fundamental, please can someone tell me what to do.

Does your Zeus BB have 35x1 printed on the cups? (or 36x24)?

How far did you (gently/hand) screw the ISO left cup in? Did it feel quite snug, or was it loose? I assume the same cup on both sides.

In theory you could salvage two left (adjustable) cups from a pair of ISO bottom brackets which should be fine for all but some of the modern cartridge BBs.

But, first verify you actually have a French BB and not Italian.

Oh, also measure the width of your BB shell to the nearest MM.

I'm guessing you're building a full Zeus bike? And now since you've confirmed the proper thread, perhaps continue on the ebay search for a Zeus bottom bracket, sell off the French threaded unit.

(Suggest to double check the shell, possibly Italian thread)

An excellent reference source: Sheldon Brown's Threaded Bicycle Bicycle Bottom Bracket Crib Sheet

English/ISO cups are slightly smaller diameter than metric (French/Swiss) thread cups.

No standard English/ISO bottom bracket came with right-hand thread fixed cups, so either you're mistaken, or a previous owner cross-threaded the fixed cup side. You seem to know what you're doing so I'll assume that the shell may have been cross-threaded.

If the threads aren't too badly damaged, you could, as CliffordK suggests, use an adjustable cup on each side. If the cup doesn't seem secure in the damaged threads, you could use a threadless cartridge, such as is available from Velo-Orange and others, or ream and tap the shell for Italian thread and use Italian thread cups with a spindle for a 68mm shell to get the proper chain line.

If the OP's metric 35mm diameter cups are too large to fit, then Italian 36mm diameter cups will also be too large. I suspect a cross-threaded English shell.

I don't know of a single instance of a ISO/BSC bottom bracket being threaded right on both sides. However just about anything is possible. For example the builder might have somehow loaded 2 RH taps onto the tool and followed through with the mistake, though I'd expect that he'd have noticed.

Or the BB might have started out 35x1 and gotten stripped, and retapped to BSC, but intentionally RH on both sides to avoic shaving out too much metal when reversing the helix.

Either way --- assuming the OP has his facts right -- the solution is to use 2 left cups and lockrings, and move on.

Reading this , its British [ISO] rethreaded but both are RH?

Yea Not original owner we guess it's history.

agree : Get 2 adjustable Cups and Lockrings* ..

I have a set of Edco Italian Thread Aluminum lockrings and 'CUPS' for their cartridge BB

*that was what they used (those pieces for Postage~$7? )

This site is awesome, thanks everyone for your response.

I can confirm both shells on my Zeus are right hand threaded.

The non-drive side hollowtech cup I tried, fitted both left AND right shell on the Zeus frame. Drive side fitted perfectly; non-drive needed a bit more force but no damage occurred.

Shell width is 68mm

No markings on the new cups except Zeus and Made in Spain.

It can't be an Italian shell because the hollowtech cup I tried would just rattle around in there right? Correct me if I'm wrong.

No sign of cross-threading/damage.

Annoyingly, the old cups were forcibly removed and disposed of by my LBS before I had chance to stop him. Having them might have helped somewhat.

I still wonder if you have a French shell.
And Italian BB cups. And the ISO BB seems to thread in, but isn't the right one.

Hopefully I'll have some French parts to play with tomorrow.

It looks like Zeus is a bit terse with their markings, and do make both French and Italian parts. I'm not quite sure how to verify that you have Italian without careful measurement. The Italian BB should be 70mm wide (and might be a problem if you wish to just exchange BB cups.

Do you have measuring callipers? A large (quality) adjustable wrench?

English thread Zeus cups are marked "B.S.C."

Italian and French cups are unmarked, but the 1mm difference in diameter should make it clear which is which.

Interesting theory because I just assumed they were French cups because that's what they were advertised as on Ebay. However the shell definitely is 68mm

It's difficult to believe I have an ISO shell with RH threads.

I do have digital calipers and a wrench. Do you know what measurements I should be getting? Cheers

Interesting...thank you. More convinced they may not be ISO. I'll get my calipers out again.

If I were you, I'd take the old cups to a machinist, so that he could check the pitch diameter with a set of 1-2" pitch micrometers, and get the thread pitch on an optical comparator.

"Annoyingly, the old cups were forcibly removed and disposed of by my LBS before I had chance to stop him. Having them might have helped somewhat."

Nothing like trashing the evidence.

-----

This discussion seems a bit overwrought.

All that is necessary is to run a set of metric taps through the shell and you will be able to use the metric cup set you purchased.

BSC/ISO has a pitch diameter of 34.85mm and metric a pitch diameter of 35.0mm. So even if both sides really are ISO RH it is moot.

-----

I suspect that for many, finding a mechanic within reach who has such tools may be a challenge.

English cups should be 34.8mm OD
Metric (French/Swiss) cups should be 35.0mm OD
Italian cups should be 36.0mm OD

I wonder if the OP is missing the simplest and most logical explanation.

Namely that his new "French" BB is really Italian".

This would be consistent with all his observations, and is easy enough to confirm with the naked eye.French and Italian BB threads have very similar major diameters, so the OP can use his known English as a basis of comparison, and the similarity or difference will be obvious.One of the problems with trying to help people on the forum is that we're stuck with the information they present. Poor, incorrect or incomplete information has everyone scrambling so solve a mystery, when none in fact exists.Sometimes it can elicit a poor or counterproductive solution, such as retapping a RH thread to LH.

I have enough information to help me solve this so I'd like to thank you all for contributing. No need to reply unless you have a revelation...!

Digital calipers tell me the cups I bought are indeed French.
That my shell sides are both RH, suggest it is French but doesn't explain why the cups don't start.
Even though I no longer have the old cups, there was definitely a fixed and an adjustable one
Next step (despite the above logic) is to obtain 2 ISO adjustable cups and forget this whole debacle.

Thanks again xx

My measurements were about:

BBs
English/ISO, OD of cups, 34.7
French, OD of cups, 34.95
Italian, not measured, but about 36mm

Shells
ISO ID: About 33.8
French, about the same, hard to get a precise measurement.

My ISO bb screwed about 3/4 the way into the French shell before binding.
The French cup screwed about 2 or 3 threads into the English shell before binding.

It is possible someone re-tapped your frame to ISO, both sides for some reason. In which case, the obvious choice would be to tap RH threads to both sides.

There's always one!

Thank you, Clifford, you have been most helpful and your measurements and observations match some that I have also made. Someone retapping both sides to RH ISO is believable until you remember the old/discarded BB was complete (one fixed and one adjustable). In any case, it is what it is, and your solution of re-retapping is one that I will go with. The French BB I bought off EBay wasn't cheap, and I would like to use it.

Thanks Again

I wouldn't re-tap it. I suppose it is possible, but I'd use whatever fits properly. I was just thinking that someone previously might have forced 2 english cups into it, or tapped it to English. But, you don't want to mess up those threads, otherwise you could lose the whole bike.

Maybe take it back to the shop that took the old BB out for a second opinion. And... also ask them to dig around their recycle bin for your original parts.

This is Italian thread

Replace with an Italian thread BB
(and sell the French BB to someone who needs it)