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  1. #1
    mtbr member
    Join Date
    Nov 2012

    chain rings and shaft that cranks bolt too have small wobble?

    in ringsI just took my chain off to clean it and found that when I spin the peddles of peddle the bike with my hand that the 3 front chain rings have a small wobble.

    Now what I did was I removed the 2 allen bolts that seem to hold the crank arms on as well as them being pressed on,and found the the shaft that goes through the BB on the bike in witch the crank arms are mounted too has a hole going all the way through it,and is hollow,and when I again turned the crank arms,I found that the hollow shaft seemed to be wobbling also but this could just be the hole drilled off center in this shaft??

    Now this is a 2012 Spesh rockhopper comp29 and I have never crashed or road off road its new with 70 miles on it

    Also I hear some light noise when I spin the cranks some times as if dirt and sand got in there and the 2 allen bolts that bolt on each side of the crank has a hole going through them allowing dirt and water to get in the center of this crank shaft and as I spun the cranks I saw water rolling around in there since I just washed the bike,but again there are holes in each allen bolt so dirt can get in

    ITS live far away from a bike shop so any help would be appreciated,and also a few bike shops I talked to said that there bikes do this wobbling of the chain rings also as things get knocked out of wack,but as long as the bike runs ok then its fine.

    Now my bike shifts easily and fast,and I have no chain slippege or even noise when peddling,and I was also told that its normal for chain rings to wobble a little bit to help the chain move up and down themselves??

    So could it be a off center hole in the center of the crank shaft that makes it look like its wobbling?

    Am I in trouble??

  2. #2
    Plays with tools
    Reputation: customfab's Avatar
    Join Date
    Jun 2008
    How much runout do the chainrings have, do they all appear to be bent at the same spot and in unison? You might have a bent tab on the crank arm that's pulling the rings out of alignment. Unless your bottom bracket spindle is bent it's not causing your problem.

  3. #3
    mtbr member
    Join Date
    Nov 2012
    Yes I pulled the bolts out that hold the crank arms on besides the arms being pressed on,and looked through the center of the crank shaft in witch the crank arms attach too and found that it is wobbling a bit as well.

    So I talked to a bike shop and found that this can happen and as long as it does not effect the bike working properly then I am ok to ride it and then I can bring it in to replace the bottom bracket,but I will do it myself as its nothing to do.

    I watched some youtube videos and learned how to do this job,since I rebuilt my dirt bike engines and frames components myself as well as restore cars,this is nothing.

    I purchased the required tools,witch is a universal crank arm puller and internal bottom bracket wrench and allready pulled the bottom bracket out in 20 minutes,inspected everything and reassembled it.

    I then took the bike for a ride and the bike shifts up and down the gears fast and smooth,so I am going to just run the bike some more,and then install eithet a new internal
    BB or an external BB and a Shimano XTR chain set with the hollow tech BB I think it is?

    I also used a dial indicator and checked the faces of my bike frame BB area and its level and smooth all around so I will not be facing it,as I did not want to remove the protective coating from the alluminum frame leaving it to fall prey to oxidation.

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