Friday, 3 January 2014

Square Taper Left Hand Crank Arm Stuck On

Mobile bicycle mechanic job of the day, removing a left hand crank arm without the use of an extractor tool. But why?
The crank arm needed to be removed, but there was no thread taped in the arm, for the crank extractor tool to screw in and do it's job!
This bike was booked in for a service and chain slipping. After a road test and pre-checking bike over, it was found to need the "drive chain replacing" Cassette, chain, chainset and bottom bracket.
Read our article on Chain wear & Care

This left hand crank-arm has no thread to allow for the extractor tool to screw in and remove arm.
(Cheaply manufactured)

Without re-tapping a thread, the only way to remove;
1. Is by cutting a slot along the back of the arm

 2. Using a chisel to split open the cut 
And then hit the back of the arm with the chisel to remove the arm of the square taper axle.

Note the position on the square

When replacing a worn left hand crank arm:
  • You will need to make note of the position of the square (As photo above) in the crank arm so it aligns with the right-hand crank position, 
  • And the length are the same size, will be marked on the inside of the arm. near pedal thread.


2 comments:

  1. Just ride it for a while with the bottom bracket bolt removed. The arm will wiggle loose then be ready to fall off. I have done this many times to remove arms with stripped threads.

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  2. Thank you for your comment! As a professional mechanic we don't recommend the above comment/procedure. This is likely to miss-shape the crank fitting or result in injury to the rider. As you can see from the post, the arm is fitted on a tapper, the alloy crank arm has reacted with the still axle resulting in a chemical reaction welding the two parts together and riding the bike with no fitting bolt is not going to make the arm fall off!!!

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