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  1. #1
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    Problems with Chainring and Chainline

    For the fun of it, I'm converting an old Raleigh Grand Prix to fixed gear. I'm having two issues:

    Chainline: I attempted to set the chainline by spacing the cog the same distance from the center of the hub as the distance from the center of the seat tube to the small chainring, but it seems pretty clear that the cog is outboard of the small ring (among other things, the chain occasionally hits the big ring.) The frame doesn’t seem to be bent (but then the bike had been abandoned at my LBS). Is there a better way to set the chainline or should I just try to eyeball it?

    Chainring bolts: My chainring bolts have come loose each time I have ridden the bike more than five miles. Is this a common issue? If so, what causes it? I see there is a recommendation in the fixed tips sticky to use blue locktite on the chainring bolts – is that the solution to this problem?
    Any help would be appreciated.

  2. #2
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    Photos, charts, measurements, and recommendations: http://sheldonbrown.com/chainline.html

    More good advice: http://www.sheldonbrown.com/deakins/...ttingchainline

  3. #3
    i like whiskey
    Reputation: innergel's Avatar
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    Quote Originally Posted by DA07079
    For the fun of it, I'm converting an old Raleigh Grand Prix to fixed gear. I'm having two issues:

    Chainline: I attempted to set the chainline by spacing the cog the same distance from the center of the hub as the distance from the center of the seat tube to the small chainring, but it seems pretty clear that the cog is outboard of the small ring (among other things, the chain occasionally hits the big ring.) The frame doesn’t seem to be bent (but then the bike had been abandoned at my LBS). Is there a better way to set the chainline or should I just try to eyeball it?

    Chainring bolts: My chainring bolts have come loose each time I have ridden the bike more than five miles. Is this a common issue? If so, what causes it? I see there is a recommendation in the fixed tips sticky to use blue locktite on the chainring bolts – is that the solution to this problem?
    Any help would be appreciated.
    What rear wheel are you running? Is this a dedicated fixed gear wheel or is it a converted road wheel?

    Chainline: If you have 120 rear spacing, a standard road double on the inside ring should give you a 42mm chainline. That is pretty much standard. You say the chain is hitting the big ring. Do you still have two rings on the front? If so, take off one of them and replace the bolts with BMX/shortstack chainring bolts.

    Bolts: I've never heard of chainring bolts coming loose. Maybe they are too tall? Try some different bolts (see above) or see if you can find a washer to take up some space. Locktite might work, but not if they are not seating down the entire way.

  4. #4
    hello
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    Since this is a conversion you're doing, you need to re-dish the rear wheel and respace that hub axle to bring that cog in line with the small ring.

  5. #5
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    Quote Originally Posted by BianchiJoe
    Photos, charts, measurements, and recommendations: http://sheldonbrown.com/chainline.html

    More good advice: http://www.sheldonbrown.com/deakins/...ttingchainline
    Thanks. I actually started with Sheldon Brown's site. (In fact, I'd never heard of a fixed gear before I saw his discussion.) I followed (or think I followed) his instructions for measuring, spacing and dishing, but the chainline still doesn't seem straight. I'm beginning to think the rear triangle may be bent even it it doesn't look that way.

  6. #6
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    Quote Originally Posted by innergel
    What rear wheel are you running? Is this a dedicated fixed gear wheel or is it a converted road wheel?
    It's a conversion, but I got really lucky -- the rear wheel was track threaded on the left. It's a Brompton hub, 27" steel rim.

    Quote Originally Posted by innergel
    Chainline: If you have 120 rear spacing, a standard road double on the inside ring should give you a 42mm chainline. That is pretty much standard. You say the chain is hitting the big ring. Do you still have two rings on the front? If so, take off one of them and replace the bolts with BMX/shortstack chainring bolts.
    The measurement between the fork dropouts is 126mm. Perhaps the right side was bent out 6mm at some point.

    I can take off the big ring (and figure I will at some point), but I'm kinda glad I haven't yet since that was one indicator that the chainline wasn't straight. (Otherwise I would have been inclined to believe the measurements over the appearance.)

    Quote Originally Posted by innergel
    Bolts: I've never heard of chainring bolts coming loose. Maybe they are too tall? Try some different bolts (see above) or see if you can find a washer to take up some space. Locktite might work, but not if they are not seating down the entire way.
    I'll try taking it apart and using some spacers.

  7. #7
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    Quote Originally Posted by roadfix
    Since this is a conversion you're doing, you need to re-dish the rear wheel and respace that hub axle to bring that cog in line with the small ring.
    Thanks, that's what I'm trying to do.

    My first attempt, basing the spacing (and subsequent dishing) on the measurement process recommended at http://sheldonbrown.com/chainline.html, didn't seem to work. Is there another way to determine the appropriate spacing (other than just eyeballing it)?

  8. #8
    i like whiskey
    Reputation: innergel's Avatar
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    An easy way to check your chainline is to mount the crank and lay a straightedge against the front chainring. Run it back to the cog and you'll be able to see how far off you are.

    I'm not sure how you are going to run a fixed gear on a converted freewheel. I know you said the opposite side has a fixed thread, but that seems like more trouble than it's worth. Why don't you run SS and just get some spacers? You'll get your chainline spot on without having to redish. Just move the spacers around.

    And go get the proper chainring bolts. They are inexpensive, look better and will make your life a lot easier.

  9. #9
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    Some suggestions:

    1. yes, "eyeball" is easier, and accurate enough. Measurement can be tricky. If you get in front of the chain ring and sight back along the chain, you can see pretty clearly if the chain makes a bend coming off the chainring.

    2. You can check rear triangle alignment pretty easily. Tie a long string to one dropout, wrap it around the head tube, then tie it tightly in exactly the same position on the other dropout. Make sure it's tight. Measure the distance from the string to the seat tube on each side; if they're not the same, something's bent.

    3. 126mm was standard dropout spacing for a long time -- 6 and 7-speed freewheels.

    4. I suggest you remove the big ring, get some short stack bolts to attach the small ring, check frame alignment, and if it's okay, get a straightedge and figure out how much you need to move the cog, then re-space the axle that much, re-dish and you're good to go. My guess is you goofed up somewhere in calculating the chainline measurements.

    If the cog is too far outboard, as you say, you may get lucky. Maybe you can just move the little ring to the outboard position where the big ring is now, and everything will work without further ado. I'd certainly try that first.
    To the last I grapple with thee; from hell's heart I stab at thee; for hate's sake I spit my last breath at thee.

  10. #10
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    Quote Originally Posted by DA07079
    Thanks, that's what I'm trying to do.

    My first attempt, basing the spacing (and subsequent dishing) on the measurement process recommended at http://sheldonbrown.com/chainline.html, didn't seem to work. Is there another way to determine the appropriate spacing (other than just eyeballing it)?
    You got rid of the freewheel cassette and are running a single fixed cog on that hub, right?

  11. #11
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    Quote Originally Posted by innergel
    An easy way to check your chainline is to mount the crank and lay a straightedge against the front chainring. Run it back to the cog and you'll be able to see how far off you are.
    Thanks, I'll try that.

    Quote Originally Posted by innergel
    I'm not sure how you are going to run a fixed gear on a converted freewheel. I know you said the opposite side has a fixed thread, but that seems like more trouble than it's worth. Why don't you run SS and just get some spacers? You'll get your chainline spot on without having to redish. Just move the spacers around.
    I may not have been clear. I'm calling it a "conversion" because the bike was a 10 speed. I've already taken the 5-speed freewheel off, flipped the wheel, and threaded on a track cog and lockring. I've also already moved spacers oround and redished the wheel -- unfortunately, not for the correct spacing.

    Quote Originally Posted by innergel
    And go get the proper chainring bolts. They are inexpensive, look better and will make your life a lot easier.
    Please forgive my ignorance, but what are the "proper chainring bolts"? I haven't done anything to change the bolts (as far as I can tell, the bolts had moved in the last 30 years until they started loosening on me).

  12. #12
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    All the tricks to move ring in?

    Have you done all the tricks to move your chainring in closer to your bottom bracket to get better chainline? Assuming this is the direction you need to go. Flip your axel around so the shorter side is on the drive side. I recently cut the teeth off a large chain ring and mounted this on to the crank on the inside and then the small chainring onto this, used the original chainring bolts and this moved me a couple more mm in towards the frame and got the chainline acceptable. It was not the prettiest way to get it done, but it worked and the bike is a bit of a beater for rain rides so looks were not paramount. This is probably not the best of ideas, but on a project (SS conversion), I screwed a BB lockring on first, then the SS freewheel and this brought the chainline out slightly and along with the earlier steps line things up well. Good luck
    Fred

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  13. #13
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    Quote Originally Posted by JCavilia
    1. yes, "eyeball" is easier, and accurate enough. Measurement can be tricky. If you get in front of the chain ring and sight back along the chain, you can see pretty clearly if the chain makes a bend coming off the chainring.
    Thanks, I'll do that, along with the straightedge suggested above.

    Quote Originally Posted by JCavilia
    2. You can check rear triangle alignment pretty easily. Tie a long string to one dropout, wrap it around the head tube, then tie it tightly in exactly the same position on the other dropout. Make sure it's tight. Measure the distance from the string to the seat tube on each side; if they're not the same, something's bent.
    Great, I'll measure before I try to adjust the wheel. I remembered seeing something like that but didn't remember the process.

    Quote Originally Posted by JCavilia
    3. 126mm was standard dropout spacing for a long time -- 6 and 7-speed freewheels.
    I saw that, but the bike had a 5-speed when I got it (which doesn't mean much) and (from what I can tell) was before this model was made as a 6-speed. I'll measure the frame alignment as you suggested and then I'll know.

    Quote Originally Posted by JCavilia
    4. I suggest you remove the big ring, get some short stack bolts to attach the small ring, check frame alignment, and if it's okay, get a straightedge and figure out how much you need to move the cog, then re-space the axle that much, re-dish and you're good to go. My guess is you goofed up somewhere in calculating the chainline measurements.

    If the cog is too far outboard, as you say, you may get lucky. Maybe you can just move the little ring to the outboard position where the big ring is now, and everything will work without further ado. I'd certainly try that first.
    It's quite possible that the measurements were goofed up somewhere, but if so, I've managed to reproduce the same mistakes quite a few times. (This doesn't rule out a mistake -- especially if the mistake is in my subtraction rather than the measurements.)

  14. #14
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    How about some photos so we don't have to keep going around in circles?

  15. #15
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    Quote Originally Posted by roadfix
    You got rid of the freewheel cassette and are running a single fixed cog on that hub, right?
    Yes -- on the other side from where the freewheel was since that side has the left-threads for the track lockring.

  16. #16
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    Quote Originally Posted by DA07079
    Yes -- on the other side from where the freewheel was since that side has the left-threads for the track lockring.
    Photos....

  17. #17
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    Thanks everyone for the suggestions

    I think I've got enough direction for the next time I'm able to play around with it:

    1. Check the frame alignment via the string method suggested above.

    2. Swap the big and little rings or remove the big ring and use some short-stack bolts.

    3. Using straightedge and eyeball, move the spacers around until the chainline appears straight.

    4. Redish as necessary.

    I'll let you all know how it turns out.

    Quote Originally Posted by roadfix
    How about some photos so we don't have to keep going around in circles?
    Unfortunately, I don't have a camera I can use right now. (And the most puzzling issue -- the loosening chainring bolts -- wouldn't show up in a picture.)

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