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  1. #1
    NT... Big Difference...
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    Rubbing Against The Chainring

    I put a new crankset on my 1986 Trek 400 Elance. It is an Avocet touring triple with the matching bottom bracket- the rings are 52-42-26.

    I had been riding the wheelset from my 1985 Trek 720- with a Helicomatic freewheel. I assumed that the noises I was hearing were the spacing on the freewheel and the chain rubbing on cogs. It is an non-indexed freewheel- and I'm using Accushift 6 speed- so such a problem is likely to exist.

    I just threw the wheel from my 1985 Trek 620 on there- and I started getting the same noise... Now this is an SIS 6 speed Shimano freewheel, so I put it back on the stand and did some more listening- and then I realized... - so when the chain is on the smallest 2 cogs it's the chain rubbing on the big chainring.

    How do I remedy this? I was thinking of some sort of spacer between either chainring and the crank.... is that about right?


    Oh, and of course pix or it didn't happen.








    *Recipient of the 2006 Time Magazine "Man Of The Year" Award*

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  2. #2
    Senior Member
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    I've also been not leaving things alone and getting not quite perfect results. Tried some new brake levers on the serotta, bad idea, and an extra cable later im back to the old brake levers. so I have the skill to take a working part off and put it back on, but I don't yet have the knack of fitting new pieces and being able to adjust them properly. there's an art to this wrench game.

    I don;t have an answer for you, but I wish you luck\

  3. #3
    I love the rolling hills. ThermionicScott's Avatar
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    So the chain rubs against the big ring when you use the middle ring with the smallest two cogs? My hunch is that the crankset is just too far inboard to use the middle ring cleanly with the whole freewheel. If you try to use thin chainring spacers to move the middle ring further away from the big ring (as my stock Deore LX crankset came to me), then you may create the same trouble for the granny ring. A longer BB spindle might clear up the problem, but then you'd increase the Q factor, for what that's worth.

    Were I in that position, I would probably just leave the hardware alone and try to use the big ring with more of the middle cogs instead of the middle ring with the two smallest. In theory, that would be a little more efficient and nicer on the chain, too.




    (Or put less complicatedly, that noise is your bike telling you to shift into the big ring. )
    Last edited by ThermionicScott; 06-24-15 at 05:52 PM.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
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  4. #4
    Senior Member RobbieTunes's Avatar
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    More lube.
    Quit listening.

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  5. #5
    NT... Big Difference...
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    Quote Originally Posted by RobbieTunes View Post
    More lube.
    Quit listening.
    Rub some dirt on it and drive on,trooper.


    Hooah. Reenlist. All American. Airborne. All the way.
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  6. #6
    Senior Member Paramount1973's Avatar
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    What's your chainline?

  7. #7
    Casual Student of C&V J.Oxley's Avatar
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    Quote Originally Posted by ThermionicScott View Post
    (Or put less complicatedly, that noise is your bike telling you to shift into the big ring. )
    +1

    With something like this I try to adjust the rider instead of the bike. Much easier.
    Bike repair was so simple when we were all so ignorant we didn't know we couldn't do it. -- FBinNY

  8. #8
    verktyg verktyg's Avatar
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    In a lot of situations 10 speed, 12 speed, 18 speed, 21 speed, and so on are just marketoid fantasies. On many old 10 speed bikes, 8 different gear combinations were all that was practical.

    The rule of thumb was DON'T USE BIG-BIG, SMALL-SMALL sprocket combinations.

    Modern bushingless chains have a lot of lateral flexibility, also, they are generally narrower. Short chainstays compound problems.

    verktyg

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  9. #9
    Senior Member jeirvine's Avatar
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    If the chain is the original chain, I would switch to a modern 8 speed chain, where the pins are more flush with the plates.
    The man who dies with the most toys…is dead. - Rootboy

  10. #10
    rhm
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    multimodal commuter rhm's Avatar
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    If there's any extra thread on the adjustable cup, you can put a spacer (same spacer as is used behind afreewheel or Sturmey Archer cog) behind the fixed cup.
    Another option is a bigger middle chainring, making this into more of a granny-and-a-half-step arrangement.

  11. #11
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    TGB, A wider BB, spacer(s) on the fixed side of the BB and/or chain ring spacers for the large chain ring. I also wonder if reversing the middle chain ring or the outer chain ring might not give some extra space between the two, I'm not familiar with the Ofmega/Avocet crank sets.

    Brad

  12. #12
    Senior Member 70sSanO's Avatar
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    According to Sheldon Brown's Bottom Bracket Size Database:

    Ofmega cranks, including those branded "Avocet" use a non-standard spindle, thinner than either J.I.S. or ISO spindles. As far as I know, nothing else works.

    If it is non-standard, it is not as simple as getting a longer spindle. If you are getting rubbing on the last "2" cogs I doubt a narrower chain will give you enough clearance.

    I think you have to live with it or figure out a way to move you chainline. My vote is to put a thin spacer on the drive side and move the cup out a bit. At the same time you could put a thin spacer on the drive side of the rear hub and re-dish the wheel a tad. You may have to adjust the non-ds hub spacing.

    I'm not familiar with the details of the cog spacers used in a Helicomatic freewheel. An even more drastic measure along with the above would be to replace the cog spacers on the highest gears with slightly thinner ones. Obviously you don't want to honk up the original spacers.

    In the end you just need to move the cogs toward the non-ds and the chainrings toward the ds. Unfortunately it is infinitely easier running a 7 speed cassette on a newer freehub.

    John

  13. #13
    verktyg verktyg's Avatar
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    Quote Originally Posted by jeirvine View Post
    If the chain is the original chain, I would switch to a modern 8 speed chain, where the pins are more flush with the plates.
    +1

    @ Golden Boy The chain pictured on your bike has exposed rivets and expanded side plates like these.

    ShimanoUniglideChain.jpg SRAM-PC-870Chain.jpg

    A chain like this with almost flush rivets may work better...

    SRAM-PC-48Chain.jpg


    Does the rubbing on the large chain ring occur when you are in the middle chain ring with the 2 small sprocket on the rear or just the smallest chainring?

    I've built up a lot of triples over the years and found that when there's a lot of size difference between the smallest chain ring and the largest, many times the chain is going to rub on the large ring.

    A lot of pre 1980's triples used 3, 4 or 5 tooth differences between the middle and large chainrings for 1/2 step gearing plus a small granny gear for hill climbing.

    During the MTB boom, triples started coming with evenly space tooth count on the chainrings: 48-38-28t and so on.

    The "MTB" style chainring combos usually have less of a problem with chain rub on the large chainring while the granny gear style usually does.

    Two solutions that I've used:

    1. Get a larger granny gear, say a 30T instead of a 26T and a smaller large chainring. I run 48, 49 or 50T larger chainrings. (In Golden Boy's case, those drilled rings are too pretty to mess with).

    2. More realistically, accept that you're only going to be able to use the smallest chainring with 3 or 4 of the rear sprockets.

    1/2 Step with a Granny Gear:

    TouringCranks.jpg MotobecaneGrandJubile1980 007.jpg

    MTB evenly spaced style:

    Colnago1988Technos 006.jpg Bianchi1990Mondiale 017.jpg


    Another thing to consider is frame alignment. This probably doesn't apply to @golden boy because Trek frames were jig built and properly aligned but a misaligned rear triangle from either an accident or being improperly spread to use a wider hub will cause lots of problems with chain rubbing. It might not show up on a double but a triple magnifies the problem.

    The rear wheel needs to be parallel to the plane of the frame and front wheel. The rear wheel has to be properly dished too and sit evenly spaced in the rear triangle.

    If the plane of the rear cogs isn't parallel to the chainrings then that can cause problems in both the front and rear.

    verktyg

    Chas.
    Things aren't always what the seem... Don't believe everything you think!

    Chas.

  14. #14
    I love the rolling hills. ThermionicScott's Avatar
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    Huh, I didn't look closely enough at the chain the first time around. Get a SRAM PC-850/870 on there and see if that clears it up!
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
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  15. #15
    Senior Member gaucho777's Avatar
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    Quote Originally Posted by rhm View Post
    If there's any extra thread on the adjustable cup, you can put a spacer (same spacer as is used behind afreewheel or Sturmey Archer cog) behind the fixed cup.
    +1. I think this is the simplest, most cost-efficient approach. Sounds like you probably just need to move the crankset ~1-2mm out from the frame to give the chain enough clearance to avoid rubbing the large ring. The spacers come in different thicknesses (1mm, 1.5mm, 2mm, etc.). Before heading to the LBS, you can do a test run without the spacer by loosening the fixed cup, then re-adjust the adjustable cup, and measure the gap between the BB shell and fixed cup to determine the correct size spacer required.

    Considering the drop from the middle to small ring, I'm surprised you aren't experiencing the same issue with the small ring x 2nd cog. Chain rub isn't an issue in the smallest ring?
    Last edited by gaucho777; 06-25-15 at 01:21 PM. Reason: typo

  16. #16
    A Roadie Forever 79pmooney's Avatar
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    Does the chain actually engage with the big ring? If not, just ignore the sound. I'll guess yo could ride the next decade on the middle to next to smallest without issue. That middle to small will get picked up about every blue moon but aht you could leave the front derailleur with a touch of rub and it would work fine.

    That said, I caution you against putting too many miles on that crankset. I broke mine across the pedal hole climbing. (Perhaps you should ignore me - I've broken every piece of Avocet gear I have ever ridden. Maybe others have had better luck.)

    Ben

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