Alloy BB's

[sidmarx]

Looking at replacement alloy bottom brackets, what's the longest pedal crank i can reasonably expect to find==18 cm, or maybe longer?

[bobtravers]

Well, usually you can find some 170, 172, 175 mm (almost 18 cm)

Might look for "chain set", since the "bottom bracket" is the bearing set that allow your chainset to spin onto...

http://cdn.mos.bikeradar.com/images/bikes-and-gear/components/chainset/Chainset_shim_lx-670-75.jpg

BB bearing are the thing found in the middle of this image, 2 other parts are chainset and crank...

[Sparky]

Peter White Cycles ( http://www.peterwhitecycles.com/carmina.asp ) sells TA cranks. They are available in arm lengths up to 185mm. They are a bit pricey, but they are very nice, too.