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Old 10-01-06, 12:05 PM   #1
becnal
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Replacing middle ring on Trek 720

I ran into a friend of mine in the park today, and when I complimented him on his nice bike, he told me he was going to get rid of it. After looking shocked and awfully sad, I noticed the middle ring was broken and seemed to be missing a whole inch of teeth.

I told him it would be a shame to get rid of an otherwise perfectly good bike, everything else works fine, and I offered to fix it for him. So, my question is:

Should I replace the middle ring only, or put a new set on it?
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Old 10-01-06, 12:47 PM   #2
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Originally Posted by becnal
I ran into a friend of mine in the park today, and when I complimented him on his nice bike, he told me he was going to get rid of it. After looking shocked and awfully sad, I noticed the middle ring was broken and seemed to be missing a whole inch of teeth.

I told him it would be a shame to get rid of an otherwise perfectly good bike, everything else works fine, and I offered to fix it for him. So, my question is:

Should I replace the middle ring only, or put a new set on it?

if the middle ring is the only thing broken would replacing the ring fix the problem? are you sure teeth are missing....some shimano rings are made that way.

ed rader
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Old 10-01-06, 12:52 PM   #3
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If it looks like teeth got knocked off of hte middle ring in an accident, then replace it. If the middle ring's teeth are otherwise really worn out (people with triples usually spend most of their time in the middle ring) then replace it. Check and see if the chain should be replaced too.
Partly this goes back to, why was your friend wanting to get rid of the bike? What did he find not worked well?
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Old 10-01-06, 02:35 PM   #4
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Well, it all depends. Is it the touring 720 from the 80's, the higher-end sister of the 520? Or is it the more recent 720 "multitrack," the low-end MTB/hybrid of the last decade or so? If it's the former, just replace the middle ring unles the whole crankset is damaged. It's the latter, the rings are probably riveted together anyway, and the whole set would need to be replaced.

Of course, it seems hard to believe that a steel chainring could be so badly damaged, or that you would want to compliment someone on the Multitrack,which is a pretty pedestrian machine. So I'm assuming that it's a touring 720. Replace that chainring! And if he still doesn't want, take it off his hands and give it a loving home. It's a great bike, it'd be a shame for it to go unridden.
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Old 10-02-06, 01:10 AM   #5
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The broken middle ring is preventing him from shifting out of granny gear.
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Old 10-02-06, 07:07 AM   #6
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Depending on the model, you many have to replace the whole crank. My daughter has a mid-'90's Trek 730 Hybrid (actually a step up from the 720) and the chainrings are riveted to the crank spider and aren't replaceable.
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Old 10-02-06, 07:18 AM   #7
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Depending on the model, you many have to replace the whole crank. My daughter has a mid-'90's Trek 730 Hybrid (actually a step up from the 720) and the chainrings are riveted to the crank spider and aren't replaceable.
Right now, Nashbar has Nexave square-taper cranks for $35 or something... those are 22/32/44 with replaceable chainrings and hollow arms. That'd be a great replacement crank for a low-end MTB!
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