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Old 09-11-10, 04:01 PM   #1
Canadian
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Metal on metal sound that only occurs in the big ring - BB?

I just bought a craigslist sale (Scapin, images posted in this thread).

When I bought the bike, I wiggled and jiggled the headset and BB, and rode it around a little in the parking lot. It had almost no air in the tires and I didn't bring a pump, so it was hard to give it a go. Everything seemed fine, though.

This morning I took it out for a rip and discovered a metal-on-metal, very low pitched "chug-chug" sound every 11 o'clock pedal rotation when it's in the big ring. I tried to move the gears around and duplicate it in the smaller front ring, but no matter how much I tried to duplicate it in the small ring I was unsuccessful. It is a regular occurrence in the big ring.

I cannot see any chain rub in the front derailleur when it's in the 11 o'clock trouble spot, and I don't know where else to look for metal on metal. This is presumably a BB issue? When the bike is stationary, I cannot wiggle and jiggle the problem in the BB, it still seems perfectly tight to me. I don't know much about mechanics, so any words of wisdom are appreciated!

(I asked the guy very specifically if there were any headset or BB issues, he said no. I'm pretty confident he was telling the truth, because the way he spoke, he seemed to not have much knowledge about bikes, and bought it because he knew the parts were high end.)
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Old 09-11-10, 04:54 PM   #2
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From the timing, my first guess is that the crank arm is hitting the FD cage. It would only happen on the big ring because that's when the cage is outboard. Check that first.

Otherwise bring the crank around to the right position and take a close look at the section of chainring about to engage the chain. there might be a bent or cvhipped tooth there that makes the sound as it engages.
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Old 09-11-10, 05:29 PM   #3
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Originally Posted by FBinNY View Post
From the timing, my first guess is that the crank arm is hitting the FD cage. It would only happen on the big ring because that's when the cage is outboard. Check that first.

Otherwise bring the crank around to the right position and take a close look at the section of chainring about to engage the chain. there might be a bent or cvhipped tooth there that makes the sound as it engages.

Thanks, FBinNY! Your first guess was right on. It's funny how closely you can look at something and not "see" it until you have an informed eye. The old 600 derailleur is quite bent. (Though do mechanics sometimes intentionally do this to deal with gear issues that might arise from mixing old and new school parts?)

I have a Dura Ace front derailleur that is the right clamp size for this bike. Do the number of gears matter for front derailleurs? I bought the Dura Ace FD for a 9 speed cluster (it was the wrong clamp size for that one), this is a 7 speed. They are both double rings on the front.
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Old 09-11-10, 07:15 PM   #4
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9 & 10spd front derailleurs are narrower, so don't use the 9spd one.

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The old 600 derailleur is quite bent. (Though do mechanics sometimes intentionally do this to deal with gear issues that might arise from mixing old and new school parts?)
Yeah, as a last resort... but the fact it's visibly bent seems to indicate a hack job... maybe you can tweak it better, but be careful - the steel used for the cage is usually pretty brittle.
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Old 09-11-10, 07:36 PM   #5
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9 & 10spd front derailleurs are narrower, so don't use the 9spd one.


Yeah, as a last resort... but the fact it's visibly bent seems to indicate a hack job... maybe you can tweak it better, but be careful - the steel used for the cage is usually pretty brittle.

Thanks, Kimmo. I'll keep an eye out for a compatible FD to replace it.
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