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Crankset Upgrade Issues

Old 08-06-20, 05:13 PM
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Fujosh
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Crankset Upgrade Issues

This is my first build, and I've run into a couple problems,

I am building my road bike from a 1981 Fuji Sports-12 frame. I upgraded from the original crankset to a Shimano SORA R3000, but when I re-assembled the bike, the chain has tons of slack when its on both of the smallest rings. It didn't have this problem on the old crankset, so I'm wondering if the smaller front ring on the new set is just smaller in diameter, causing more slack? The Rear wheel is actually set further back in the dropouts now, so I don't think that is the issue. I want to be sure this is the issue before I take out some of the chain links.

I'm also having an issue with the friction shifters... They shift just fine when I turn them, but are immediately pulled back to their original position and the bike shifts back. Should I be setting the cables when the shifters are already pulled all the way down?

I appreciate any help. Thank you

p.s. I would upload photos but apparently I need to post 10 times before it allows me to.
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Old 08-06-20, 06:15 PM
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dsbrantjr
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Do not shorten you chain unless you are certain that it will be long enough to go onto the big front/big rear combination. If you have a small ring with fewer teeth than the old one you will have more slack with the same length chain, but don't shorten it without checking big/big; you may need a derailleur with a higher takeup capacity.
https://www.sheldonbrown.com/deraile...ent.html#chain
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Old 08-07-20, 01:37 PM
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Fujosh
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Yes, Still using original derailleurs. Thanks for the reply and reference material
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Old 08-07-20, 03:04 PM
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adamrice
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Originally Posted by Fujosh View Post
I'm wondering if the smaller front ring on the new set is just smaller in diameter, causing more slack?
You could check this yourself by counting the number of teeth. And chainrings almost always have their tooth count stamped on them to save you the time. In any case, it is very likely that the new rings are smaller, just because of prevailing trends in the industry.

I'm also having an issue with the friction shifters... They shift just fine when I turn them, but are immediately pulled back to their original position and the bike shifts back. Should I be setting the cables when the shifters are already pulled all the way down?
Not sure what you mean here. The friction shifters need to be snugged down enough that the derailleurs' return springs can't pull them back. If you loosened the D rings on the shifters, perhaps that's what's happening. But you shouldn't need to loosen/tighten them for every shift.
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Old 08-07-20, 04:24 PM
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Put your chain on BIG ring & cog.
See how much slack you have with my quick method.
You want a minimum of 1" slack to be safe.
Excess can be removed.
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