Bottom Bracket spacer question

Forums Mountain Bike Forum Bottom Bracket spacer question


This topic contains 5 replies, has 3 voices, and was last updated by Profile photo of Syd Patricio Syd Patricio 7 years, 2 months ago.

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  • #77737

    Ok here is the situation. Originally I bought a tassajara gary fisher on ebay for pretty cheap a while back. I have since upgraded to different wheels and some other components on the bike. I decided about a year ago to start learning how to repair bikes on my own since I also have an older schwinn moab that could also eventually be fixed up. Anyhow, eventually I broke the crank set’s middle cog (bent a tooth and made a gouge in the cog). At first I thought that I could replace just the cog but it turned out that the cogs are welded together on the original crank set.

    I looked into buying a full crank set and found a deore shimano crank set(octalink splined) with bb(bottom bracket) for very cheap on ebay. Anyway, before I did all the homework that I should have and had installed the sucker, I realized that it was the wrong size bb. I realized this when riding, the crank arms would tighten to the point where I could no longer pedal, so I knew something was wrong. I compared to the original square tapered bb and noticed that the octalink was much shorter. After getting a second new bb from my LBS (the first one they gave me was isis rather than octalink) I thought I finally had a good fit, until I started to notice a wobble to the whole thing. Basically, there is a slight wobble so when pressure is put on one side or the other there is a little "play" in it.

    So, I am under the impression that I need a spacer to correct this wobble. I am wondering what size spacer, and which side it goes, cup or non-cup. I am posting some pictures to illustrate my situation, sorry for the blurryness on the underneath photo (measures 72mm on the frame part where the bb goes, not sure of term here). The original bb is a square tapered, measures about 81mm from end to end with the cup on it as seen in photo. The bb below the original one is the one that came with the crank set and the box is for the bb that is currently installed (shimano deore ES51 118×73 bb). Any ideas on what size spacer, which side or other thoughts on what I should do to fix this problem?



    Thanks for any advice, sorry for the long post



    I can’t tell which size spacer you need. I can tell you this. Applying spacers to the drive side will affect your "chain line." Chain line is the path which your chain runs in various gear combinations. If your chain line is off, certain gear combinations that should be available to you, won’t be. Or worse, you’ll have a hell of a time getting your changers dialed. Since, you are running three rings chain line is bit more finicky. Generally, when you set chain line you start in the middle ring and the middle cog on the cassette. The two "should" be in the exact same plane. Since no two frames settle in exactly the same way, this is unlikely if not impossible. There’s a lot of nuance to it, that I have yet to master. It took me about a dozen tries to get my hardtail’s chain line squared away. On the other hand I got my DH sled on the first shot.


    Thanks for the reply. it does seem a little tight to the frame when in the lowest gear on the front rings, so maybe i should just start with a couple spacers of different size, try em out to line up the chain line? i assume the spacers go on the outside of the derailleur flange? do most LBS have these in stock? Maybe i should just ask at the LBS. Thanks for the input.


    There are two common shell sizes 68 mm and 73mm on the Octalink it clearly shows it is a 68…You pretty much need the 73mm to get a correct chain line. double check by using a tape measure and measure the bottom bracket shell, from the right face to the opposite side.


    These are the four most common sizes for shimano. It would be wise to contact Gary Fisher and aske them which one of the bottom brackets did they use for the 2008 model year bike.. If you check the archives it shows they used a shimano 442 crank with an octalink bb.

    Spindle Length/Case Width: 113mm – 68mm

    Spindle Length/Case Width: 118mm – 68mm

    Spindle Length/Case Width: 113mm – 73mm

    Spindle Length/Case Width: 118mm – 73mm

    #77742 … 616032.PDF

    cut and paste that link and go from there it will give you the right information

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