The dimensions of the bracket.
During assembly ( Image 44/47 ), of a new crankshaft must take into account the following sizes:
- The screw thread of the bracket-pot.
The most common format is a bracket-pot with thread BSC 1:37 “x 24 TPI. The thread on the right has left hand thread, the thread left has right hand thread. The bracket can also have French thread M35 x1 with on both side right-hand thread or Italian thread 36 mm x 24 TPI with on both sides right hand thread .
- The width of the bracket-pot.
These can be 68, 70 or 73 millimeters. The bottom bracket, which is mounted has to fit in the width of the bracket. By flattening, bracket can be slightly narrower. mount a crankshaft that belonged to the original width of the bottom bracket. A bracket having a width of 69 mm had an initial width of 70 mm.
- The chain line.
The distance from the chainring to the center line of the frame is determined by the crank shaft, which is mounted ( figure 48 ). The correct distance from the chain line is dependent on the distance of the sprocket to the axis of the sprocket wheel. In the manufacturer information, is what is the distance of the chain with respect to the center line of the frame. When the derailleur gear chain line is the distance from the center of the chain wheel block to the center line of the frame. At bottom bracket units with both sides sleeves with washers ( Figure 49) to set the chain line a few millimeters.
- The shaft length.
With the replacement of the crank shaft, the shaft length must be equal to the old one. For example we will convert a complete derailleur system from 2×8 to 3×9, it is possible that a different axial length to be mounted. As part of a double chainring Shimano Ultegra an axle length of 109.5 mm. we are going to transform this now to a triple execution there must be an axis of 118.5 mm can be mounted.
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