I just bought a Specialized Langster and I notice the chainline is off by about 3 cm. I need to move the chainring inward to get it right—but I can't move it to the inside of the spider, or it will be off in the other direction. My question is, can I adjust the crank spindle at all? It's a sealed cartridge with square-tapered spindle.
—LANGuiShing left of cenTER
Off by three centimeters!? Ye gods, it's a miracle you can pedal that single-speed more than six feet without throwing the chain. I'll assume for now that you meant three millimeters.
To answer your question, you can't adjust the spindle inward or outward by conventional means. With a Shimano or Shimano-style cartridge bottom bracket, you can only remove it completely, hurl it far away with a cathartic scream (feel better now?), then buy a new one in the spindle length you need. However, the Langster comes with a 103 mm spindle, and you'll be hard-pressed to find one shorter than that. Maybe you could change the bottom bracket and the cranks together—to some track-classic set such as Sugino 75—but I've heard of Langster owners having crankarm/chainstay clearance problems when they try that.
So what to do? You might be able to safely use an old-school trick. Back before cassette freehubs, when all freewheels screwed on, you could get a spacer to place underneath the freewheel to move it out a millimeter or two. Freewheels and bottom bracket shells have the same diameter (as long as both are English thread), so you could use the same spacer(s) between the bottom-bracket shell and the lip of the right-side cup, to move the spindle outward. Then you could move the chainring inside the spider, and voila—you do it all over again with one more or one less spacer. But eventually you get the perfect chainline.
Now all you have to do is call around and find a shop that still has such spacers (and maybe also Prince Albert in a can). If young whippersnappers tell you there is no such thing, don't give up. This is a case in which—unlike the old hippie/boomer slogan—you can't trust anyone under 30.
Now just in case you did mean three centimeters, I'll bet you bought the bike used, not new. (You didn't say which.) If so, I'll bet someone blew up the original bottom bracket and bought a replacement carelessly—so instead of the original 103 mm, you have a 122 mm intended for an early 90s mountain bike. You'll just need to find a 103 mm, and I hear tell that FSA makes a good one. You might also check the rear hub and right crankarm against what's spec'd for Langsters on the Specialized web site, to see if those parts have been replaced.