Chain alignment of cassette-type SS cog w/chainring- Mtbr.com
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  1. #1
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    Chain alignment of cassette-type SS cog w/chainring

    OK Guys,

    I'm about install my rear wheel.

    It's a SS hub, but with the cassette-type interface, not a thread-on.

    I have a boone Ti Cog (yes, I know, stupid expensive, i got it used for cheaper),
    as well as the boone spacers.

    I'm concerned about chain-line. I'm replacing a Surly rear wheel with thread-on cog,
    and my chainline never dropped, but it would pop every once in a while, I presume from
    less than perfect chainline.

    I have an Eno crankset, and a very wide BB spline (118?).

    What is the easiest way to get a perfect chainline? I'm decent, but not expert in my
    mechanical abilities, so small words so I can understand are appreciated.

    Thnx.

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  2. #2
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    Its very easy to do. The rear chainline is set using spacers on either side of the cog.

    The key to getting it perfect without frustration is buying a spacer kit with a sufficient amount of thin spacers like this. This will allow you to fine tune your chainline and also can be used for chainlines that are outside of the normal range

    Beware of the spacer kits like this that only have 2 spacers as they force you into a particular chainline (which probably works with most modern 50mm chainline cranks but not necessarily with your setup)

  3. #3
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    Quote Originally Posted by ncj01
    What is the easiest way to get a perfect chainline? I'm decent, but not expert in my
    mechanical abilities, so small words so I can understand are appreciated.
    I second the advice on having a bunch of thin spacers, I have a Spot brand kit with plenty of different sized spacers that allow sufficient adjustment.

    I install the cranks on the frame, install the rear wheel and then place the bike vertically (fork end straight up) in my stand.

    I drape the chain over the crank and let it hang over the rear cassette, when it stops swinging, that is where I want the rear cog.

    Cheers,
    Marty

  4. #4
    one chain loop
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    67.5mm rule

    I made a little instuctional before. Hope this helps.
    everything sucks but my vacuum cleaner.

  5. #5
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    Quote Originally Posted by marty_hd
    I install the cranks on the frame, install the rear wheel and then place the bike vertically (fork end straight up) in my stand.

    I drape the chain over the crank and let it hang over the rear cassette, when it stops swinging, that is where I want the rear cog.

    Cheers,
    Marty
    Now that is one good idea !! I always just use a long straight-edge held on the side of the chainring but I think yours is an easier/more accurate way, as long as the bike is really vertical.

  6. #6
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    I put the cog on without spacers, fit the chain, spin the cranks a bit with the brakes dragging (or using my hand).

    Where the cog ends up is marked with a pencil. Then I space it to that line.
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  7. #7
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    Good idea's All....

    thnx!

    While there's a few that I may try, still not exactly what I was looking for.

    I spent some time late yesterday reading Sheldon Brown's website, and finally found what I think is the
    most percise method.

    See, my chainline (photo'd above) "looks" perfect. Visually I can't detect it being less than perfectly straight.
    But it does "pop" every 20-revolutions or so, as though it's not perfectly alighned.

    Sheldon's recco, as best I can tell it:
    1) Measure front chainring's exact distance from center of frame/BB - write that down (lets say it's 54mm)
    2) Measure exact inside-frame at dropout side to side (with wheel installed), write that down - it'll probably be 135mm

    now it starts to get complicated

    3) Take 1/2 of inside-dropout side to side...say 135/2 = 67.5mm, write that down
    4) We know we want the rear cog to be exactly 54mm from the centerline of the frame
    5) We know the centerline of the frame is 67.5mm from the inside edge of the dropout
    6) Subtract front chainring width from cent (54mm) from rear drop to center (67.5) for 67.5 - 54 = 13.5mm
    7) Use series of spacers to make the rear cog teeth exactly 13.5mm from the inside edge of the dropout
    for a dead perfect chainline


    I'm not sure if I've said that right, but I think thats how it's done.

    I have 2 sets of spacer (Boone and some generic black ones), plus the Boone cog itself is off-center of it's base, so
    by flipping it, you change the position.

    I hope to get crazy with a ruler, protractor, set of calipers, and a sledgehammer if necc tonight. We'll see how it goes.
    Last edited by ncj01; 12-04-2008 at 08:25 AM.
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  8. #8
    aka baycat
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    Use the Rennen kit. Two "collapsible" spacers. You can adjust them to get the perfect chainline. As I was not really keen on a bunch of calculations and spacers, just eyeballed it. Not had a problem since day 1.

  9. #9
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    The measurement method is prone to inaccuracies in the measurement and calculation. Basically it's a cumbersome way to end up with a chainline, and you can make mistakes. Very few people agree on the centreline of a frame tube.

    If your chainline is correct and you hear popping from your chain riding up on the rear cog, it's probably because the chainstay is flexing.
    As little bike as possible, as silent as possible.
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  10. #10
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    Quote Originally Posted by Velobike
    The measurement method is prone to inaccuracies in the
    measurement and calculation. Basically it's a cumbersome way to end up with a
    chainline, and you can make mistakes.
    You are definately correct. If a person doesn't measure correctly - they will get a poor result.

    If a person makes a mistake, the outcome will not be correct.

    So the question becomes one of:
    *are you prone to make more mistakes by "eyeballing it" or by using a set of digital calipers?

    I suppose that varies from person to person.

    Quote Originally Posted by Velobike
    Very few people agree on the centreline of
    a frame tube.
    Thats why you use the center of the BB shell.


    Quote Originally Posted by Velobike
    If your chainline is correct and you hear popping from your chain riding up on the rear cog, it's probably because the chainstay is flexing.
    Maybe.

    The key part to your phrase is: If your chaining is correct.

    We'll never know if it's correct or not w/out doing the measurement method (correctly of course).
    I don't think eyeballing it...is "verification" that it's correct.

    I think it's very unlikely that frame flex is causing chain popping. At least in this case.
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  11. #11
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    My preferred way of confirming chainline, once everything is installed, is to slowly rotate the cranks with the bike on the stand. Look at the chain leaving the ring and cog, and see if the teeth are dead center within the chain link or biased to one side or the other. Adjust accordingly.

  12. #12
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    Quote Originally Posted by ncj01
    I don't think eyeballing it...is "verification" that it's correct.

    I think it's very unlikely that frame flex is causing chain popping...
    The eyeball tells you whether the cog is running slap bang in the middle of the chain. Are you going to trust your measurements without checking that?

    I used to measure it all, and then realised I was relying on the final eyeball check to prove it correct.

    BTW when I used to measure, I got the tube dimension with a calliper. I then measured from the edge of the tube to the centre of the chainring, and added half the tube dimension. This gives a more repeatable measurement than guessing the tube centre.

    At the dropout end, if you want to measure, then you should ensure that the frame is perfectly aligned. It's not unknown for there to be a slight lateral displacement so that the centreline through the dropout is not dead centre on the frame. If you are using the measurement technique, you should allow for this being a possible factor.
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  13. #13
    one chain loop
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    now we are talking anal PERFECT. since frame flexing is inevitable, there is really no such thing as perfect dead on zero chainline. but what we are trying to do is to minimize that parallax error (eyeballing) by using measuring tools. let's say you screwed up looking for the center of the frame by +/- 2mm, it is still not bad enough to throw your chain off. but if you think you did everything right, measured everything and still having troubles with skipping chain, then blame it on your crappy misaligned frame.
    everything sucks but my vacuum cleaner.

  14. #14
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    Quote Originally Posted by fishcreek
    now we are talking anal PERFECT. since frame flexing is inevitable, there is really no such thing as perfect dead on zero chainline. but what we are trying to do is to minimize that parallax error (eyeballing) by using measuring tools. let's say you screwed up looking for the center of the frame by +/- 2mm, it is still not bad enough to throw your chain off. but if you think you did everything right, measured everything and still having troubles with skipping chain, then blame it on your crappy misaligned frame.
    Yeah - I think that it's easy to get overly obsessive about stuff like this (and frame angles, wheelbase, chainstay lengths..... .). As I said, I just use a steel straight-edge on the side of the chainring and see where that ends up at the rear wheel, set it all up like that and eyeball it as a check. Then go out and ride it. Always works for me, I never have any chainline issues.

    On the other hand, I do know of some people who set the rear sprocket slightly inboard of correct so that under high load situations, when the frame flexes the most, the chainline will be more correct. Seems a bit over the top to me, mind you.

  15. #15
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    Quote Originally Posted by fishcreek
    now we are talking anal PERFECT. since frame flexing is inevitable, there is really no such thing as perfect dead on zero chainline....
    Exactly!

    Which is why I use the method I described earlier - it gets just as good a result without the faffing around with measurements.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  16. #16
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    Quote Originally Posted by Andy R
    On the other hand, I do know of some people who set the rear sprocket slightly inboard of correct so that under high load situations, when the frame flexes the most, the chainline will be more correct. Seems a bit over the top to me, mind you.
    I guess the problem with that would be that the frame will flex/sway in both directions...on the down-stroke of each side.
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  17. #17
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    Well, campers...after all that, I got some reality therapy.

    Let me say/admit, I think ya'll were mostly right.

    I started off with the digital calipers, a calculator, and pen/paper.

    I quickly said to hell with all that, and just started eye-balling it. I got it on there what i thought was pretty good, then I spun the cranks good, back-spun for a while, and repeated several times. In each case the rear teeth were to the outside edge of the chain.

    I played musical spacers with about 2/3rds the width of a chain...I got it to where the cog would sit to the left side of the chain most of the time, sometimes closer to the center.... I coudn't get it to rest exactly in the middle, i chaulk this up to just the chains natural tendendy to "walk" across the middle of the chain-roller...

    I can note that "visually" the chain line looks idential with each setting/position... the spin-it-out and let it stop method seemed more accurate.

    I also am running lesser chain-tension that I usually do/did...

    FYI, no pops. Not sure if that's due to chain alignment improvements...or lesser (better) chain tension...or both.

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  18. #18
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    Just one anal comment - your chain connecting links have the open ends facing in the direction of travel.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  19. #19
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    Now I find that highly annoying.

    I specifically built the bike with both ML's facing backwards:



    Although...and this is complicated, you have to closely read my bike-review linked above...I made the mistake of just dropping
    my bike at a LBS and saying: "DO IT"... with regard to several items, including the wheelset, cranks, thru axle converions,
    brakes, etc. I have been struck by LBS grease-monkey-itus... I got the bike back, was disgusted with the wheelset due to
    the $$ i paid, quickly got rid of them, replacing with I9, hence the cog and this spacing thread...but my personal failure was
    to note that they re-installed my chain backwards.....NEWMAN!!!
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  20. #20
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    Quote Originally Posted by ncj01
    ...I specifically built the bike with both ML's facing backwards...
    I noticed that (in your first pic) which is why I thought it might be worth pointing out to you.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

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