ColonelJLloyd 

Here's what I'm working with.

• 120mm spaced frame
• Stronglight 49d crank arms with single 48t 3/32" ring
• Fixed/fixed hub with 1/8" cogs
• 68mm English BB shell
• 1/8" chain

I'm going to buy a JIS taper, symmetrical cartridge BB. Now, class, what length spindle would you choose?

photogravity

118mm? I'd probably go narrower, if possible. I recently pulled a 103mm off the front of the Bilenky, but it uses a Specialized chainset.

kc0yef 

113mm Sutherlands 2nd edition

Spoonrobot 

Keep an old cup & cone BB around so you can mock up the crankset and get a value for X. Failing that, start long and then you can space the chain-ring in to pretty much whatever you want.

ColonelJLloyd 

I don't follow.

113mm sounds like the ticket. Thanks!

RobbieTunes

I'd get any old JIS taper BB to guage it. Mount the R side cup and bearings, slide the spindle through, install the crankarm.
Look at your clearance to the chain stay for the single chain ring. That's about your only worry.

If it's close, use it.

If it's too long, guage the extra length, double it.
Ex: 4mm too long on the R means your spindle is 8mm too long.
Adjust for asymmetry.

If it's too short, guage the extra needed, double it.
Ex: if you need 4mm more length, you need 8mm more spindle.
Adjust for asymmetry.

Eyeballing works as well as anything, if you're sober.

rhm

My guess is the 113 will be too long.

ColonelJLloyd 

I suspect the crank arm will hit the BB shell before the ring will hit the chain stay. I'm trying to figure out spindle length for the best chain line. I don't have a spare cartridge BB to dry fit.

Could be. I am using a model 93 with a single ring in the outside position on a French frame (68mm shell) with a 107mm JIS BB (symmetrical) and the inner chain ring tabs are super close to hitting the chain stay. That's not an issue with the 49d, though. Sutherland's just lists "Stronglight" cranks so I guess they're suggesting that all Stronglight cranks fit the same distance between outer ring and BB shell for a given spindle.

So, you'd go with what spindle? 110mm? I'm afraid that with a 107mm I might be getting close to bottoming out the arm on the BB shell.

rhm

Heck if I know. Thinking about it now, I have seen Stronglight cranks sit far inboard of other cranks, so maybe you'll be fine. I do know the last three BB's I've bought were longer than desired. No doubt this was my fault.

lostarchitect 

I'd try what I had on hand and see if it needs to be shorter or longer than that. Then you'll know about what you need.

elguicho 

Love this comment

ColonelJLloyd 

I don't have any 1.37" x 24tpi cups on hand, hence all the figurin'.

Italuminium

Yes, Robbie, but dealing with propietary french frivolities is much more bearable with some vin, biere ou cognac!

due ruote 

I agree the 113 is likely too long. I'm using a 114mm JIS taper with a #93 double and have about 12mm clearance between the 53 ring and the stay.

110 seems about right if you're worried about the 107 being too close. Alternatively you could get the 107 and add spacers if necessary.

ColonelJLloyd 

True, but spacers increase the likelihood of the NDS arm bottoming out on the BB shell. I guess I'll roll the dice with a 110mm spindle.

Velognome 

I think you need to know the position of the cleanest chainline on the original set up and measure the distance from a fixed centerline on the frame and do the same with the fixed, mocked up, and then subtract the difference and multiply by two



.....ahhhh Hell, it's still a guess at best.

norskagent

get a phil BB = adjustable.

ThermionicScott 

Isn't the Shimano 110mm BB asymmetrical in some way?

ColonelJLloyd 

Yeah, that'd do it. Pricey, though. How much adjustability do they have?

I'm not sure. I was going to go with a VO, which I think are symmetrical.

ThermionicScott 

Here's what I was thinking of... DS length is the same as the "107": https://web.archive.org/web/201010220...ttom-brackets/

(For Shimano, at least.)

nlerner

I'd roll the dice with a 108mm spindle and have a couple of 1mm spacers on hand.

lostarchitect 

I've got a bunch. I can send you some if you want.

ColonelJLloyd 

Nah, thanks. I'm a risk taker.

norskagent

I think the phil BB has 5mm of adjustability. But I wouldn't want all 5 sticking out on side or the other!

Velognome 

The last SS conversion I did was from a double chainring late 70's Raleigh. The distance of the stock outer ring was 5+mm off the stay, to get a clean chainline, running 1/8" chain, the new ring ended up being 3+mm off the stay. So maybe it needs to be 4 or so mm shorter than it originally was, or so I thought! But, I was wrong!!!!


The resolution was to go to my LBS with his favorite brew ( chilled, 15 minutes before closing time), told him what I was trying to do. He then grabbed a box of spindles and cups and began searching for a good line, once he found it, measured the spindle and order the BB for me. In the end, I paid for the BB and the install, We drank some excellent Belgium Triples and I got a clean chainline without the use of spacers...which somehow makes me feel good about the decision.