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Discussion Starter · #1 ·
BB are very confusing to me.:madman:
I just can't figure out how to know if I'm going to buy the right one. This is what is on my C-dale Jekyll.
Shimano BB ES-50.

What do I look for when I go shopping?
What tool do I buy?
Recomondations?
 

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I'll assume you are not using an outboard bearing crankset. To know what bottom bracket you need, you will have to find out the interface type and spindle length. The three types of BB are ISIS, square taper and Octalink. Get yourself a crank puller and bottom bracket tool for a cartridge type bottom brack (these are pretty standard tools). Then, remove the cranks and look at the crank interface, it should be obvious if they are square taper. If they use a spline fitting then it is either ISIS or Octalink. If the cranks are branded Shimano and use a spline fitting, they are Octalink. All other makes of cranks with spline use ISIS. Now remove the bottom bracket using the BB tool. The spindle length is normally printed on it, if not, use a pair of calipers or a rule to measure the length of the axle. Now go and buy the correct bottom bracket!!
 

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Old man on a bike
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A Shimano ES-50 is a splined bottom bracket of the Octalink variety, for use with appropriate Shimano cranksets (or those licensed by Shimano) of the same series. You need to find the width of the bottom bracket shell on your bike; it's probably 68 or 73 mm and of an English threading (standard for most mtb's). The spindle length may vary with your specific crankset, so post the model of your crankset to be sure (it's usually imprinted on the back of the crankarm if it's a Shimano model). Together the bottom bracket shell size and spindle length will give you enough information to order the correct bottom bracket. The ES50s come in 68x113 and 118 and 73x113 and 73x118 I think.
 

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Discussion Starter · #4 ·
The crankset is Shimano XT's.
This is what is on the BB.
68
BC 1.37 X 24
113

So, I can order any Shimano, Octalink 68 X 113?

Thanks for the replies.
 

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Old man on a bike
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The 68mm is your bb shell size, the 113mm is your spindle length, the BC 1.37x24 indicates an English threading. Just saying your cranks are XT isn't all that meaningful, as there are many generations of XT. Be model specific (it would appear as FC-Mxxx), although not needed at the moment.

Now, why are you shopping for a new bottom bracket in the first place? What is making you think you need a new one?
 

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Discussion Starter · #6 ·
I had to run out to the garage and get it.
FC-M752

The reason I need one (or think I need one) is the whole crank has movement. You can grab the crank arm and see the spline move up and down.
 

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You've properly installed/torqued the arm, then see the play? Can you see any deformation of the spline interfaces of the arm/bb?
 

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Discussion Starter · #8 ·
I'm sitting here in my computer room with both the BB, crank arm and magnifing glass. I looked, then had my wife look. Both look good. No unusual wear or deformaties.
 

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gateCrasher said:
When measuring the crank case (ie, 68mm or 73mm), what exactly do you measure? Are you measuring the width from the outside, or is it an inside measurement?

Thanks,
/gC
It is called the bottom bracket shell. Outside width of the shell without the BB installed. No way to get an "inside width."
 
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