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  1. #1
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    Is this rear triangle misaligned?

    I bought a brand new, leftover 2010 Marin Muirwoods 29 back in November of last year. Not satisfied with the stock gearing, I decided to swap out the stock crankset (28/28/48) for a mountain crank with 22/32/42 rings. I purchased a Shimano Alivio square taper crank, Shimano Un54 BB (68 x 110), and Alivio front derailleur. Upon installation and set-up of the front derailleur, I had a really hard time getting things adjusted.

    The chainline was all wrong. In the granny ring, the chainline was running straight back to the 4th cog (counting from the large cog and its 8 speed). When I shifted to the large cog, the chainline was noticeably deflecting towards the non-drive side which isn't right. I had a heck of a time getting to the chain to not rub the inside of the derailleur cage and had to back the low limit switch all the way out.

    The trouble continues when I shift to the middle chainring. Usually, I can adjust the front derailleur where it runs little or non running the chain to the big cog on the cassette. It was rubbing on the 3rd largest cog! I finally managed to adjust it where the chain rubbing on the inside of the cage was minimal on the #2 cog.

    Last, when I was adjusting the high limit screw, I ran into more problems. Because I had to back the low limit screw all the way out, it required me to dial a little big of cable tension in so that I can get the chain shifted all the way up to the big ring. So, when I am running on the large ring and the small cog, I have quite a bit of cable tension to keep the chain from rubbing the outside of the cage.

    The way this was drivetrain was running was not acceptable. I was even getting some ghost shifting because the chainline was so out of whack. I decided to switch out the bottom bracket for one with a narrower spindle, a 107. That helped just enough to get rid of the ghost shifting and allowed me to readjust the front derailleur and it is a little better. The bike is ridable, but it still doesn't seem right and I get a little bit of chain noise in gears I wouldn't normally expect the chain to be so crossed up. The chainline is acceptable in the following combinations:

    Granny gear - top 3 cogs
    Middle ring - middle 4 cogs
    Outer ring - bottom 3 cogs

    I should be able to run the granny gear in the top 4 or 5 cogs, middle gear across the entire cassette, and the outer ring across the bottom 4 or 5 cogs. I didn't have the stock gearing long enough to really pay much attention and notice the same issues, but I swear it wasn't as bad. I suspect the stock crank/bb had a narrower q-factor which made for a better chainline.

    After swapping the BB, I started to think maybe the rear hub wasn't spaced properly until I started looking at the frame and I checked the dish of the rim which was perfect. After I mounted some really big tires, I realized how uneven the chainstay clearance was (yet the seat stay clearance was even on both sides).

    So, I took the bike into the shop where I purchased it. The looked at it and said everything looked fine. This shop does not have a frame alignment gauge, so they weren't able to verify the alignment with actually measurements. They said they had an alignment gauge on order and I could bring the bike back to them to verify, which I will. They did have a drop out alignment gauge which they said they used and it was fine. Plus, I have never had issues getting the rear wheel in and out of the frame.

    Right after I got home from the shop, I decided to flip the bike over upside down once I noticed the fender mount braze one which is dead center in the chain stay bridge. Logic would tell you that mount should be in the center-line of the frame. I was going to pull the tire off the rim thinking it would give me a better visual of whether the center of the wheel lined up with the center of the frame, but after seeing what I photographed below, I don't think I even needed to do that. The center line of the tire is pretty easy to see in the tread of the tire and it is obviously offset towards the non-drive side chainstay. Whatcha think?


  2. #2
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    Quote Originally Posted by flippin_bikes View Post
    Shimano Un54 BB (68 x 110) ... narrower spindle, a 107
    This shouldn't have made any difference with your problem. The difference between the 107 and 110 is almost entirely on the left side.

    Quote Originally Posted by flippin_bikes View Post
    The center line of the tire is pretty easy to see in the tread of the tire and it is obviously offset towards the non-drive side chainstay.
    Your wheel is installed crooked. When clamping it in with the QR, you need to center the wheel at two points: Between the chain stays, and between the seat stays. This is easiest to do with the bike sitting normally (right side up) on the ground.

  3. #3
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    Vertical dropouts??

  4. #4
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    Quote Originally Posted by flippin_bikes View Post
    This shop does not have a frame alignment gauge, so they weren't able to verify the alignment with actually measurements. They said they had an alignment gauge on order and I could bring the bike back to them to verify, which I will.
    A piece of string is all you need to check if the rear triangle is centered. Run the string tightly from one dropout forward, around the headtube, and then back to the other dropout. The seattube to string clearance should be the same on both sides.

  5. #5
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    Quote Originally Posted by laura* View Post
    This shouldn't have made any difference with your problem. The difference between the 107 and 110 is almost entirely on the left side.
    It should be 1.5 mm on each side, shouldn't it? It did make a difference, I can tell you that much because the front derailleur required readjustment after the 107 BB went in. Even though that helped, it obviously wasn't the problem and why I decided not to try a narrower spindle.


    Quote Originally Posted by laura* View Post
    Your wheel is installed crooked. When clamping it in with the QR, you need to center the wheel at two points: Between the chain stays, and between the seat stays. This is easiest to do with the bike sitting normally (right side up) on the ground.
    Negative, wheel is in the drops perfect. They are vertical drops, so there isn't enough horizontal adjustment to cock the wheel that much off center. Another thing I forgot to mention is that the bike doesn't have any balance issues or pull to one direction, at least that I have noticed. If the wheel were cocked that much to the left, it would cause me to lean and steer left ever so slightly. That is why I think the wheel is offset to the non-drive side. Redishing the rim would bring it into the center line, but do nothing for my chain line issues which I feel are the most significant issue.

    I will take your advise on using a string to check the alignment since I can do that really easily at home. I still plan on taking the bike back by the shop when they get their gauge just to make sure.
    Last edited by flippin_bikes; 04-15-11 at 07:46 PM. Reason: grammar errors

  6. #6
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    Quote Originally Posted by flippin_bikes View Post
    It should be 1.5 mm on each side, shouldn't it?
    The 107 is something like 0.5mm shorter than the 110 on the DS, and 2.5mm on the NDS.

    I think the 110 bottom bracket was meant for cheap(er) cranksets where Shimano wanted to have left crank castings with less of a bend.

  7. #7
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    Update

    Well folks, in case anybody is interested, I have an update to my issue.

    The shop where I purchased the bike got in their frame alignment gauge and I took the bike in for them to check it.

    The rear triangle was offset 7mm to the non-drive side. They told me spec is no more than 4mm which sounds like a lot to me, but this is perhaps what you are dealing with on lower end production frames. The shop is going to send the frame back to Marin, they'll check it out, and likely send back a warranty replacement frame. It stinks that I have to do this, but it sounds like they are going to take care of the problem for me.

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