You should replace both sprockets and the chain. The chain and sprockets wear as a set and sometimes a new sprocket or a new chain combined with an old chain or sprocket will skip, come off or wear unusually fast because of the difference between the new and old. The missing teeth will likely give you some issues with the chain coming off. I'm kind of surprised that you have broken teeth on both, it must've been put through some hard use. You'll want to measure the diameter of the center hole and the bolt pattern (size of the bolt holes and the distance center-to -center of two opposite holes. count your number of teeth on each sprocket. To determine the pitch of the sprocket, i copied the chart below off wikipedia. It will give you the chain pitch (measure yours) so you can order the same and get the correct sprocket with it.
Pitch (inches) Pitch expressed in eighths ANSI standard chain number Width (inches)
1⁄4 2⁄8 25 1⁄8
3⁄8 3⁄8 35 3⁄16
1⁄2 4⁄8 41 1⁄4
1⁄2 4⁄8 40 5⁄16
5⁄8 5⁄8 50 3⁄8
3⁄4 6⁄8 60 1⁄2
1 8⁄8 80 5⁄8
Notes:
1. The pitch is the distance between roller centers. The width is the distance between the link plates (ie slightly more than the roller width to allow for clearance).
2. The right-hand digit of the standard denotes 0 = normal chain, 1 = lightweight chain, 5 = rollerless bushing chain.
3. The left-hand digit denotes the number of eighths of an inch that make up the pitch.
4. An "H" following the standard number denotes heavyweight chain. A hyphenated number following the standard number denotes double-strand (2), triple-strand (3), and so on. Thus 60H-3 denotes number 60 heavyweight triple-strand chain.
Last edited by x-bird; 12-30-2011 at 03:32 PM.
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