Q & A - Front Transmission

How do I disassemble the crank?

Normally, all cranks come free from the bottom bracket axle by use of an "extractor tool". The tool has an externally threaded body, and a plunger through the middle that is also threaded so that is screws through the extractor body. If you look at the crank, the hole that you removed the allen bolt through (assuming it was the big one in the centre) carries an internal thread, to which the external thread on the extractor mates. You unscrew the plunger as far as it will go, screw the body of the extractor into the crank, and do it up TIGHT with an appropriate sized spanner. Then, screw the plunger in, usually using a 14mm spanner to do so. It will feel as if it has come up tight, but if you exert a little effort, it will "give" and start to pull the crank off the bottom bracket axle, extractor and all. When the crank is free of the axle, use a spanner to remove the extractor from the crank. Repeat the process on the other crank.

Points to watch:

Make sure there is not a washer sitting at the bottom of the recess that the extractor screws into. When you look into the recess, you should see a square hole at the bottom, with the end of the bottom bracket axle a couple of millimetres below the edge of the square hole. The recess should not contain anything else. If there is a washer there, remove it. If you try and extract the crank without, it will end in tears!
The extractor thread on the crank is in alloy, and is therefore softer than the thread on the extractor tool. It is also a very fine thread. It is important to ensure that the threads are both clean (use an old toothbrush to clean those in the crank, with a good degreaser - but wash it out immediately, as some can damage alloy surfaces if left on too long).
Ensure that the extractor goes in straight, not cross-threaded. If it goes in crossed, and you try to extract the crank, it will pull the fine threads out of the crank, fail to extract it and leave you with a very expensive workshop job, plus the cost of a new crank! For the same reason, when you put the extractor in, do it up tight before trying to extract the crank.
Although this is a simple operation, because the consequences of getting it wrong can be expensive, it might well be worth asking the shop that sells you the tool to demonstrate it's correct use: they may charge you a few pounds, but on balance, that is better than costing yourself several tens of pounds by making a mistake.