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My dad bought a 2004 Fuji Absolute hybrid used and I rode it to a DIY shop to get everything checked out. On the way, the the chain came off once (1.5mi). Turns out the right crank arm is a little bent and the seller messed with the chainring alignment to compensate.

I'd like to swap the crankset out - it's a Shimano Sora 30/42/52T (FC3303). For example, I have seen a Shimano Ultegra with the same 30/42/52T (FC6503) on Craigslist.

Are there any specific details I need to be aware of matching up?

If I keep the same tooth count, will I have to worry about replacing the derailleurs?

Thanks!

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    You'll need to check that the bottom bracket is the same between the two, which I don't think it is in this case from a quick google search. If the bottom bracket is not compatible you'll have to replace that too. – Kibbee Apr 22 '16 at 19:12
  • Thanks Kibbee! I see that if I swap the FC3303 out for the FC6500, I have to swap bottom brackets - square for V1 Spline. Cheers! – Sam Lee Apr 22 '16 at 22:03
  • Generally chain line (distance from center of bike to chain centerline) is slightly adjustable at the crankset. Other concerns are: crank length (generally 175mm, but not always) type of sprocket mounting (will the new crank come with sprockets or not?) If you are reusing the sprockets, # of bolts and BCD (Bolt Circle Diameter) measurements matters. – zipzit Apr 23 '16 at 10:48
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I'd like to swap the crankset out - it's a Shimano Sora 30/42/52T (FC3303). For example, I have seen a Shimano Ultegra with the same 30/42/52T (FC6503) on Craigslist. Are there any specific details I need to be aware of matching up?

The main detail you will have to watch out for (as indicated by Kibbee) is whether the two cranks use the same bottom bracket. Crankset attachments are standardized; however, to paraphrase Tanenbaum, there are many standards to choose from :-).

To check whether a specific crank and bottom bracket match, you'll need to know some details about the bottom bracket, such as shaft length, attachment type (square, most common, or spline) and chainline. There are compatibility charts online to help you; a good one is Sheldon Brown's Bottom Bracket Size Database, which also lists the Shimano Sora and Ultegra.

Also, check whether the new crank is compatible with the chainrings. There are different attachment mechanisms in that area, too, so you may need to swap the chainrings along with the cranks.

If you want to play it safe, it's best to buy the part at a local shop. They can tell you whether it matches or not, and, most importantly, if they tell you it definitely matches and are wrong, they'll have to take it back. Also, they'll be able to answer your questions about mounting it - or mount it for you for a fee.

Finally, note that for some attachment mechanisms, you will need a special tool for removing the cranks, called an "crank puller". I think you don't need one for the Shimano Sora, as it is "self-pulling", but better check to be sure.

If I keep the same tooth count, will I have to worry about replacing the derailleurs?

No, the rest of the drive-train should not be affected, at least not of the new BB is fully compatible. If it has a different shaft length or chainline, there might be problems (so it's best to avoid that).

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