that_was_easy

Unless I misread something I'm pretty sure that any standard JIS tapered, English threaded BB will work with my BB shell and my chainline will depend on the spindle length. The BB I'm replacing for this conversion, was a mid-80's vintage 116mm Shimano with early Shimano 600 cranks and an original Suntour 9 speed freewheel. I'm looking to determine what length BB I'll need.

-Phil Wood is within my budget, but I don't know if the 103mm (doubtful), 108mm (maybe), 111mm (??), 113mm (closest...), or other with 5mm play will do the job.
-Do BB cup/cone spacers change the orientation of the spindle or of the whole BB unit?
I'm a little confused by this, having never dealt with the situation hands on. I'm looking for additional explanations (havnig read the PW site) on BB spacing operations. Chainline and dishing are my primary concerns. More questions below. I already have my second build imagined, so having an excess of parts is acceptable, but I'd rather avoid that, if possoble.

Basically I'd really like to use this hub as it's intended (flip-flop) and so want to avoid altering the zero-dish of the wheel. Therefore I don't want to spacing the cog or freewheel. Since I don't have any alternate components for testing/benchmark purposes, not to mention wanting to do the work m'self (instead of the LBS that does my headsets), I want to make sure I compensate for any purchasing error that might leave me with incompatible components.

The frame (natually) and rear flip-flop hub (120mm naturally [plus] 3mmLx3mmR axel spacing) will have as there spacing 126mm.

-Assuming I'll be using a dual freewheel, XD2 cranks, and have a desire to keep zero-dish: what size BB spindle will I need?
-Is much going to depend on the width of my freewheel and cog or will chain flexibility take care of a discrepancy?
-In order to keep the zero dish of the wheel effective, in addition to keeping my drive train as silent as possible (reversed or not), would installing a cog and a freewheel of the same size achieve these ends (noise and good, but not perfect chainline)?
-What would you say is the difference between a good and perfect chainline?

I will be taking measurements once I have the frame back, but I'd like to present the hypothetical chicken and have the hive-mind lay me the egg. Any basic or outlandish (see what I did there? it's been a long day) adice is much appreciated.
Thanks for reading. Cheers.

sivat

1. Measure the chainline of the cranks with the original bb.
2. Determine what chainline you want.
3. Add or subtract twice the difference to figure out what chainline you need.

The chainline at the hub is effected only by the axle spacers. Dishing has nothing to do with chainline. The hub is designed to give you approximately the same chainline on either side. Keep it centered and go with it. A perfect chainline is within 1mm, but it really doesn't matter. Drivetrain noise will be effected more by the quality and compatibility of the chain/cog/chainring that a few mm in chainline.

Above all, quit making things so complicated. It's a bike. Don't overthink it.

that_was_easy

Thanks sivat. I don't want to do it, but sometimes things look exactly like a plate of beans and i overthink those all the time. My new rhyming mantra "Bike and beans do not mean a thing". Mr. Cosby would be proud.

One issue: Despite having the specs for the previous BB, I've already junked it because the races on the spindle AND on the cups were badly corroded. Do you think it wise to buy a majorly inexpensive BB to get an comparable idea of my chainline needs

I don't really have chainline wants, so much as my chainline/drivetrain needs demand satisfaction (to be distinguished from perfection...). I'm already using all 3/32" compatible components so I guess there'r no worries on DT noise. Cheers.

stinkwheel

I'm far from an expert on this but I'm also currently building a bike with a flip flop hub and ran into a similar problem (except my original BB was a cotter pin type!).

The advice I got, from people who ought to know was to best-guess the BB length, try it on and see if it works. If it doesn't fit, it gives you a point of reference to see how far out either way you are.

A couple of places also said they would exchange the BB providing it was returned in "as new" condition.

Happily, my first guess turned out to be within what I can reasonably adjust by fiddling with the chainring spacing. A fairly thin shim between the chainring and spider will shift it to pretty much bang-on alignment.

tellyho

I wish this method worked reliably. In my experience, trial and error is your only definitive solution to the chainline problem. If I were you, I'd use the BB spindle length recommended with your crank.

DMF 

Uhh.. NO. There is no standard for "spider offset" (for lack of a better term). Nor (afaik) is there a standard for the taper of a square-tapered axle - the angle, yes, but not where the taper convergence point is in relation to the nominal axle "end" (where you measure length from).

In other words, the chainline varies with specific axles and cranksets. You'll have to make a best guess, then measure and possibly adjust the axle length - or live with a less than perfect chainline.

Further, axle length is insufficient to specify an axle. Not all axles are symmetrical (though with cartridge BBs manufacturers have started to assume that they are). See Sheldon for how an axle is specified.

sivat

Actually there are two standards. JIS (Japanese Industrial Standard) and ISO (International Standards Organization) both specify both the angle and the "width" of the taper. As far as the spider, you are correct, but that is why I said you should measure the current one. You are also correct about some bbs not being symmetrical, and unfortunately there is no good database that i've found, but in my experience, all of the 103, 107, and i believe 113 bbs have been symmetrical.

DMF 

I'm aware of the standards - they specify the width and angle of the taper, but not the length (unless there's been a recent update). Typically this isn't a problem, but little things can add up.

I don't understand what that gets you except the current chainline, which should be a known standard. If the OP is unclear what the current chainline should be, he would be better off measuring the rear chainline. That's what he has to match the new one to.


At the end of the day, though, a mm or even two probably doesn't matter...

Grand Bois

Use a Sugino RD2 crank and a 103mm bottom bracket from Velo Orange.