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Pop Pop Pop When Pedaling

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Okay, I think I found the issue. Thanks guys!

See the pics below. The old and tired chain has indeed stretched and I've got some shark finning rear sprocket issues too.

The current chain is 56" w/o master link, (1/2 pitch) and has 54 links w/o the master link. The rear sprocket is also a 1/2 pitch, despite some shark finning.

I'm currently prepping the spare Westfield chain. I counted 53 links (including the master link) and it is 53 3/4" long. There is one broken roller but otherwise the chain is in great shape. I'm thinking it may be too short (without bringing the rear axle way forward.)

Keep ya posted, thanks guys!
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Will a new modern chain suffice for this application? 1/2 pitch, 3/16 width. Maybe chrome!

I don't think the "new" Westfield chain I have is going to be long enough...
 
put a different real wheel on the bike and try it again. I went crazy last summer trying to diagnose the same problem and it turned out to be the rear cog. Even though it looked fine to the eye when I replaced it with a different one the problem was gone. I literally wasted like two weekends trying to fix this problem and when I finally found it my head kind of exploded because I'd never even considered that that was the culprit.

*edit. I just looked closely at your pictures above and I'd say your rear cog is toast and your front sprocket doesn't fit your chain for some reason. I'd replace all of it.
 
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I agree with bikewhorder the Cog looks bad .. I would absolutely change that Cog out .And that streched chain(( Id hate to see you lose the Front Sprocket )) I think that chain shark fined your rear cog ..
put a different real wheel on the bike and try it again. I went crazy last summer trying to diagnose the same problem and it turned out to be the rear cog. Even though it looked fine to the eye when I replaced it with a different one the problem was gone. I literally wasted like two weekends trying to fix this problem and when I finally found it my head kind of exploded because I'd never even considered that that was the culprit.

*edit. I just looked closely at your pictures above and I'd say your rear cog is toast and your front sprocket doesn't fit your chain for some reason. I'd replace all of it.
 
solid troubleshoot; start with what is for sure, replace rear cog, should be easy enough to find one to swap out; then replace chain. most likely done deal. If not, check left/right alignment of front rear sprockets that could causie chain climb jumpy.
 
Thanks again guys. I'm already looking for a new (modern) chain and will pull that rear cog too...and use it for a coaster or Chinese throwing star or something. Yeah the chain on the chainring (as some smart person above suggested) was the dead giveaway. I couldn't believe how much the chain moves and sags on the chainring...and the chainring is practically new. The chain is THAT bad.

Now I haven't ridden this bike much since I restored it, maybe 5 miles...but the chain and rear cog are original. I'm guessing that the stretch and shark finning happened before I acquired this bike a rusty heap. ?
 
That takes lots of riding with an unlubed chain. It might have been too tight as well if the chain was too short.
 
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