Another variable in the installed position of the crank arm on the spindle is fixing bolt (or nut) torque. Torque wrenches are not perfectly accurate nor stable in their accuracy. Dirt or old lube in the threads, lube v. no lube, or worn bolt faying surfaces on teh crank arm, can affect drag as you tighten a bolt. By using charts and such we can find what parts and installation guidance might be close to providing a spec fit, but we can only verify an installation by trying it out.
Hmm, I just bought a used Sakae SX crank - I'm off on a BB oddyssey, myself.
On Sun, Feb 14, 2010 at 7:01 PM, verktyg <verktyg@aol.com> wrote:
> Jan, et al,
>
> This discussion reinforces the point that most classic bicycle components
> were manufactured with very loose tolerances.
>
> Almost all square drive BB spindles have a 2° taper. The width of the small
> end of the taper and the length of the taper are the two main determinants
> between the different standards.
>
> Aluminum is a soft malleable metal. The square in a crank arm stretches and
> the metal compresses when it is tightened onto the spindle creating an
> interference fit.
>
> Overtightening or repeated R & R can eventually cause fit problems because
> the arm is ether forced all of the way onto the spindle and the taper
> bottoms out on the mounting bolt/nut/washer or you run out of taper at the
> BB end and the arm bottoms out on the large end of the taper.
>
> Used crank arms frequently fit further onto the spindle. Quite often arms
> that have been ridden with loose crank arm bolts have been damaged inside
> the square and may never properly seat up again.
>
> Most new crank arms will fit on "most" spindle as long as the small end of
> the taper doesn't protrude too far into the arm and bottom out when
> tightened.
>
> The real problem is in the length that the spindles stick out of the BB.
> This can affect the chain line and Q-factor. Many BB spindles are
> symmetrical - they protrude the same amount on both sides. Most classic era
> double and triple spindles are longer on the chainring side.
>
> The charts on Sheldon Brown's (RIP) web site show some of the differences
> especially the one for Phil BBs.
>
> >http://www.sheldonbrown.com/harris/bottombrackets.html
>
>
> Getting back to my original statement, I've rarely found a BB spindle from
> any maker including sealed bearing cartridges that were accurate to listed
> specs. Many are off up to 1mm on the overall width or fixed cup side.
>
> I just measure 3 TA 344 spindles and the were all 114.6+ wide (SB 114.5),
> The TA 373 I measured was 117.7 wide.
>
> When you take in all of the factors, it's difficult to determine how a used
> crank arm is going to seat up until you mount it.
>
> We used to replace early Stronglight BBs with TAs because they were far
> better quality, less expensive and for us, more readily available. The 344
> spindles worked fine most of the time even though Stronglight used 118mm,
> 120mm or even 121mm wide spindles. We changed to the wider 373 TA spindles
> when we ran into chainline problems.
>
> I ran a TA double on my off road "rough stuff" bike using a Shimano 118mm
> wide cartridge for 15+ years without a problem.
>
> A few months back I bought a bike with a TA 3 arm Professional crankset. It
> had a 118mm wide Phil BB which messed up the chain line. I replaced it with
> a 113mm wide cartridge and fixed the problem.
>
> The Q-factor is a very personal thing that sometimes verges on the
> "Princess and the Pea". I like riding with a wider BB because of some
> physical issues. Don't get me started on one size fits all...
>
> Chas. Colerich
> Oakland, CA USA
>
>
> Jan Heine wrote:
>
>> I have tried combining a Campagnolo BB spindle and a TA/Stronglight crank,
>> and it worked only in one special case. I have one Campy NR spindle that has
>> a bigger taper, and the TA/Stronglight cranks fit just fine. (Ernest Csuka
>> of Cycles Alex Singer was surprised, as he had told me that this would NOT
>> work.)
>>
>> I tried to replicate this on another bike, and no luck. It appears that
>> Ernest Csuka was right, after all. All the other NR spindles I tried had
>> tapers that were a bit thinner, and the cranks slid all the way onto the
>> taper, leaving nothing for tightening them. It appears that my thicker
>> spindle was an outlier...
>>
>> Campy NR cranks and BBs are close to ISO taper, whereas TA and Stronglight
>> are JIS (which really should be called French - the Japanese copied the
>> French tapers and then made it their standard).
>>
>> Of course, good French-threaded BBs are harder to find these days. It
>> would be lovely if one could combine the superb quality of the Campy NR
>> bottom brackets with the light weight and more reasonable gear ratios of the
>> TA cranks. (TA bottom brackets weren't as good as Campagnolo...)
>>
>> If you have BSC or Italian threading, you have more BB options. Phil Wood
>> still offers French bottom brackets, if you just want to ride the bike.
>>
>> Jan Heine
>>
>
> _______________________________________________
>
--
Ken Freeman
Ann Arbor, MI USA