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How much gap should be between the crank arm and bottom bracket
#1
Hello,

I recently decided to restore an old bike I had lying around so that I could ride with my son. I'm installing a shimano MC 361 Acera crankset on a UN55 68/122.5 bottom bracket. After attaching the left crank arm I noticed a rather large gap between the arm and the bracket.

[attachment=3188]

Is this normal. Looking at another bike I am using for reference the gap appears to be less than 1/4 inch. On the one with the new parts it is 1/2" or more. I have included a picture. This is my first project and just want to make sure I have missed anything.

Thanks for the Help.
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#2
for a casual rider, this gap does not really matter as long as the arm clears the chain stay, the other side is more important as you need to maintain a good chain line, which you need to check visually after assembly and by making sure all gears can be obtained smoothly.
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#3
If the bolt retaining the crank arm on the BB is correctly torqued (usually 305-391 in-lbs), and you don't feel any play in the crank, the gap should be OK
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#4
Thanks for the replies.
I got a hex socket for my torque wrench and put them at 360 inch/lbs. They seem solid with no play.
Guess it's just my OCD that's bothered by the gap.

Tony
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#5
You did install it in the correct direction? (hey, just asking... though I guess that many BBs have the threads of one side fixed to the cartridge, so it should not be possible... I guess)
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#6
As far as I know I did...the drive side is considered the Right side correct? I inserted the BB in with the arrow pointing to the R on the drive side.

T
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#7
Quote:As far as I know I did...the drive side is considered the Right side correct?

Sounds about right to me.

Also, the gap looks OK, similar to the one on my square-taper BB and cranks. A couple of mm here or there doesn't matter much, as said before, provided the peddle end is clear of the chain stay and the chain line is OK.
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#8
If you look at the pedal distance on both sides you will see they are both away from the BB on one side the gear cluster. IF the pedal was a lot closer to the BB it would not clear the chain stay. Rotate the pedals back and look how much clearance they have.
Never Give Up!!!
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