I currently have two projects for which I'll be using Stronglight 93 double cranks with a single chainring mounted to the outside position. Neither of these bikes has a BB right now.

#1) Jeunet 630 (French threaded BB) to be used with a 46t 1/8" ring and a wheel built around the SA S3X.

#2) Motobecane mixte (I'm told English BB) to be used with a 45t 3/32" ring and a 6 speed freewheel (126mm axle)

I understand that the Stronglight 93 double calls for a 118mm, ISO taper spindle. Is that symmetrical, though? My calculations are based on a symmetrical 118mm spindle.

I'm not interested in scouring eBay for two old Stronglight BBs (one in French and the other English) in the correct spindle length. I could wait forever and not find them.

So, I plan to just buy new, sealed, JIS taper bottom brackets for each bike.

I understand that a ISO tapered crank will set 3-4mm farther out on a JIS spindle. So, if I were to run these cranks as doubles I would ideally order a 115mm spindle. But, I'm going to be using only the outside ring position, so I need an even shorter spindle.

I'm not sure of the distance between the two chainrings on a double (not one handy to measure),but I'm guessing it's somewhere around 8mm. So I would then reduce the desired spindle by that amount, right?

That would seem to indicate I need approximately a 107mm spindle for each. What do you think? Am I close? Which would you order?

Not sure, but maybe this page from Sutherland's might be of some use:

Stonglight 118mm BB spindles are +2mm offset to the drive side.

I am running a 104 crankset (uses same BB as a 93) with a 118mm JIS (Shimano UN) BB on mine. The chainline is out just a hair wide, probably 1-1.5mm, but the noticeable difference is on the non-drive side, since the UN BB is symmetrical. I may have some pics (click my sig & look at the '83 Trek 600 pic #11) where you can see this effect.

I used the 118 because i had it. If I was to replace it - the 115 would be fine. An FYI: Tange's BB are not all symmetrical, but I don't have a link to their chart off the top of my head.


And I don't agree with that Sutherland's chart. My crank fit a lot differently on the original BB than it does on my JIS. (to the tune of a 6mm shorter q-factor, or 3mm per side). I would have used the original had the cups been English threaded.

[The calculation based on my experiment: 118 original length +2mm offset = 120mm effective symm. Chainline needs to be moved in 3mm per side = 120-(3*2) = 114mm required symmetrical JIS BB]


And if you think you can run a shorter BB because you're not using the inner ring - be careful. I've done this and you may run into interference with the chainstay - not just the inner ring landings, which I've filed off, but the chainring bolts themselves. Remember, you'll be flexing the crank when riding. It may not hit on the stand.

You could ask this seller the symmetrical question:

https://cgi.ebay.com/super-light-Stro...item19c1c9270d

You can definitely run a shorter spindle because you're not using the inner ring (at least on these frames), the question is how much shorter. I considered the factors you mention. I won't be filing any part of these cranks. I needed to place the order today, so I just ordered both in 107mm. You've got to start somewhere and I can use a spacer or two if needed. The problem with spindle length questions is that the best answer is try different lengths until you get what you're after.

I'll sure be interested in your findings.

I've just gone the other way, with a Stronglight 93 onto a classic 70's Campy BB. That was a standard 68-120-SS.

This was after I'd tried to run the same crank with the original cyclo-cross/bash-guard. That required a triple axle. I used an equally old-skool Campy triple with thin cups.

In both cases, the fit was/is perfect. You can see my two steps forward, one step back progress in the thread on the "1963 Hetchins Mountain King - a progress report" to see photos.

For my next project, I'm thinking of a compact double, which would be JIS. But I have a stash of ISO bottom brackets. That nice V-O compact double looks good, but the V-O people just say, it works for some people and less so for others. Hmm. Thanks. I think?

Anyway, do please keep us posted.

Regarding a compact double, that's about all they can say. It all depends on the rider, terrain and the rear freewheel/cassette. That type of setup typically requires more double-shifts than most but I got used to it pretty quickly.

I'll be sure and report on how these bikes turn out.

More double shifts, eh? I hadn't thought about it.

In my (admittedly hazy) thinking, it was more like transposing down. If I earlier ran 52/42, then moved to 50/38. Then a 48/34 would be the same, only lower and slower.

Like me.

If you're already running a 50/38 it's not going to be a drastic change. I'm using their 46/30 crank which was a big change from the 52/40 I was using.

My experiment at the same time (see my earlier post). Campy spindle was 3mm less q than a JIS spindle using the original Stronglight BB for the Model 104 crank, halfway between the Stronglight BB and the Shimano UN JIS.

If you can get close, a Phil Wood bottom bracket offers about 0.1" (4 mm) of lateral position adjustment. The dual, opposing lock rings don't have to be perfectly flush with the shell. You can position the bearing cartridge where you want (within reasonable limits) and then tighten the rings.

I'm also trying to convert a French(LeJeune) cottered crank bike to a Stronglight 93. This Sheldon database might be helpful.

https://www.sheldonbrown.com/bbsize.html

With my morning coffee, I decided to peruse Sheldon's database. I'm certainly not able to critique the whole darn thing, but at least one item leaps right out.

The db says that Avocet, or -- "Ofmega cranks, including those branded "Avocet" use a non-standard spindle, thinner than either J.I.S. or ISO spindles. As far as I know, nothing else works."

Bullsh*t.

I ran my Avocet triple for years on, first, a standard Campy NR loose ball type, and then on an OMAS sealed-bearing type. For the record, I am a fan of the OMAS BB units. They can run standard sealed bearings, hybrid or total ceramic. I also just loaded up my Avocet on a NOS Campy NR triple BB. For other reasons, decided to go with my Stronglight 93 on a different BB. The Avocet went on and came off exactly as it should. It's standard old school taper.

I also couldn't find the Stronglight 93 or older cranks, beyond "interchangeable with TA" in the db.

We love Sheldon's site, but it isn't always perfect. FYI & YMMV.

A Phil Wood bottom bracket would cost more than either of the frames to which I'm fitting the Stronglight 93s.

The 107mm cartridge BBs arrive today. I'll report my findings. Fingers crossed.

Well, the eBay seller of the Motobecane mixte (what I think is a 1979 Mirage) described the BB threading as "English". No. It must be Swiss. %&$*! I should've know better. That said, the seller of the bike (a well established vintage bike shop in New England) should've known better than I. Anyone need a brand new Velo Orange 107mm BB in BSA threading?

I installed the French BB in the Jeunet and then the Stronglight 93. It's really close, but I think 107mm is just about perfect. Here are some pics. My math was just about right on. As Jesco says, "I ain't all the way crazy!"

Woohoo! Good thing that ring isn't mounted on the inside of the spider.

Nal

Haha! This bonehead doesn't own a Stronglight crank puller either so that one is going to hang out on the Jeunet until I buy one, but more likely pay a visit to my LBS.

Glad you found a reasonable option, Colonel. And, that's good info for us all Thanks!

For the record, here is a catalog page showing their "preferred" set up which would be a 113 mm symmetrical spindle for a Pista crank. https://farm4.static.flickr.com/3114/...28fda425_b.jpg

Contrary to their advice (for genuine Stronglight spindles, at least), I've used Shimano UN series sealed BBs for both Stronglight 93 & TA 5-pin cranks with double chainrings and have been fine with just 113 mm spindles on these cartridge sets - with offsets - where the original BBs would have used 118 mm spindles.

On the other hand... I have had issues using a TA Cyclo-Cross chainring on a 5-pin TA crank. I used what one would assume to be the perfect vintage TA #344 (double) axle. But in that case, the inner chainring guard was moved so close to the chainstay that it was pressing against it (with a 48t single ring and correct diameter guards) making almost any rotation of the crank virtually impossible.

Just goes to show, you can't second guess what may actually WORK for a given bike.