nilbog

Ok, so I just got my NOS roto crank in the mail and the square hole in it is ISO. I measured it to be about 13.6 or 13.7mm. compared to a shimano JIS square which I measured at about 14mm. From what I understand If I put an ISO crank on a JIS BB it will go on, but be off of the axle by 4.5mm. getting to my question, I pretty much have to get a JIS BB because its the best price on french threaded I can find (its the velo orange french threaded BB) should I calculate plus 4.5 when considering my axle length? for example, If the crank will hang off 4.5mm and I get a 107mm BB axle does that mean that after mounting the crank it will be set at about 111.5mm?

filtersweep

That is a long post?

Yes to your question-- but French threading? What sort of obsolete frame are you using? Good luck with your chainline.

mander

You're wrong here. Actually, your answer is not even coherent enough to be incorrect, since the idea of a crank at 111.5mm that you have just endorsed doesn't really make sense.

nibog, chainline and spindle length are two different measurements. One is the length of bb spindles, and the other has to do with the position of your bike's chainring relative to the bike's centerline (see Sheldon for more explanation). That 4.5 mm is added to chainline, not spindle length. Chainline on a bike with only a single ring is the distance of the centre of your chainring from the centreline of the bike. You want it to be around 42 mm give or take 2 or so mm. On the recommended bb length with an iso spindle, your bike would have the inner ring at around 41 mm and the outer at around 46... so the inner ring position is just about perfect.

A JIS spindle at that length will push you out 4~ mm, rendering neither ring usable on the recommended length bb. A spindle that is 5ish mm shorter than that length, on the other hand, will put the inner ring position in just the right spot. A spindle that is still 5mm shorter than that will put the outer ring in just the right spot, though at that point the crank will be close enough to the bb shell and chainstays that you run the risk of clearance issues.

I don't want to tell you which one to pick, as I'm not sure what the original recommended length ISO bb is. I recommend that you see if you can find out from the Classic and VIntage guys what the recommended bb length for ISO french threaded bbs would be for a road double application, and then go from there using the crude formula i gave above.. But I see VO has a huge range of sizes (props to them), and one of them ought to work.

filtersweep

He is asking what the effective spindle length is--- not asking about chainline. It should be quite apparent.

mander

Fair enough, sorry. I see the point now.

nilbog

I'm working with a peugeot UO-8 and my main goal here is trying to get the chainring as close to the frame as possible. As I will be putting a track wheel on an old bike and I find that is the key to a good CHAINLINE in any vintage conversion i've done. i'm just trying to figure out the math to get it to clear the frame without being to far considering the fittings I'm using. If anyone has converted a UO-8 and put in a new BB I would appreciate knowing what size spindle was used. I will get my wheels soon and before I get the BB so I can really get a good Idea of measurments

filtersweep

Actually, I am wrong. It should be about 4.5 on EACH side of the spindle---making a 107 seem like a 116.

nilbog

ugh.. I didn't even think of that. that pretty much confirms then that I have to get the 103mm from velo orange(as its the shortest one). now I'm considering filing out the square hole on the crank a little to get it on the spindle a little better. anyhorror stories about this? I'm guessing the best way would be to count file strokes and do the same for each side

scruggle

I've never tried this, but I think it is a bad idea. You're going to have to remove a lot of material to make a noticeable difference in chainline. Also, by removing material by filing by hand you're not going to get a good interference fit between the spindle and crank when you tighten your crank. Yeah, the 'splines' (corners) of the spindle will stop your crank from spinning relative to the spindle, but it won't seat very well. The odds that your chainrings will remain parallel to the frame are slim. Also, do you really want to remove material from a place under a lot of force?

mander

This is true, UNLESS the stated bb length is offset on the crank side, which happens sometimes. Yearrgh!

Nilbog, removing material from the crank sounds like a really bad idea. The fit depends on friction over a large surface area and as scruggle said, removing material in a haphazard way (since even counting strokes won't control for variation in downward pressure, variation in angle, the file getting clogged with aluminum shavings, etc) will very likely **** that up.

I'd be really surprised if you couldn't make something work with the 103 or the next size up, even if you have to futz around respacing your hub.

veganwar

Seriously, is this crank worth riding on this bike? You are converting a peugot - just get a VO french threaded BB and some sugino RDs or any of the similar cranks.

mander

^^ True dat. The VO 107mm french threaded BB will work fine with you r SHimano cranks with the ring on the outer position.