worn out sprocket?

[Cheese Whiz]

...Also, I noticed that before my second chain broke, when I moved the chain by hand it would alternately get loose and then tight. It may be that this second chain (a used one) has stretched unevenly, and may not be worth fixing, even though it's got a lot of tooth left. Or will a worn sprocket cause a chain to run loose/tight loose tight.....?

It could be more serious, a bent crankshaft would cause the tight/loose condition you describe. Let's hope it's the sprocket. FWIW, excessively tightening a chain that's hot and not untensioning it before it cools can bend a crank when it cools off and contracts.

 

[bcorradi]

Ya I don't think the sprocket is in good shape, but I also don't think its the reason your breaking chains. I've seen sprockets in a lot worse shape not break chains.

Also make sure the end of the crank is true...no matter what the husky guys say the cranks on outboard clutches are more susceptible to getting damaged (untrue) than inboards.

 

[teatersroad]

It is worn a bit, but hardly offensive. When you do go to replace it (what saw are we talking 'bout) maybe switch to the powermate system. That way you don't have to replace the whole drum when only the drive sprocket is worn, and you can plat with different pitch and gearing ratios if you feel like it.