I'm a bit of a fan of the HobbyKing 1400kv motors. Trouble is these motor's shafts are exposed and sometimes they become bent. Shaft replacement was a challenge I needed to overcome or through away motors. This is my unique and easy way of removing and replacing the shafts.
The shafts have a 3.17 mm diameter, common to quite a few motors in Hobby King catalog. Unfortunately Hobby King do not carry replacement shafts for the motors that I use. RC Timer do carry shafts for these motors, they cost a dollar each, which is quite reasonable. eBay has packs of 10 for about $2 and these are what I use. The shafts I purchased are made for a 2212 motor. They are a little shorter than the standard shaft. That's actually an advantage. As long as the shaft is long enough for prop adapter, the shorter the better. These shafts are totally fine.
The first time I tried to remove the shaft from a motor, I destroyed the motor. Needless to say, this was a fruitless exercise. Removing the shaft from the bell housing of a motor, is the most difficult part of replacing it. Traditionally removing the shaft is done in a press. Specialise presses are made to this purpose. You can adapt a vice to do the same thing, but it doesn't always work. So, after some experimentation I discovered a better method.
Pictured below is the tool of choice. I'm not exactly sure what you call one of these. It is a centre punch, but it has a spring inside (Spring Loaded Center Punch). When you press down on it, it releases shock,that causes of indentation from the point on the end. For our purposes it's the shock that doesn't work. The point does help, but will be worn away in the process. It also creates a small indentation on the end of the shaft, that helps keep the centered.
First you need to use a hacksaw to cut off the shaft.
Then its a good idea to sand the top so the end is flat.
Now remove the small circlip from the bottom of the shaft on the bottom of the motor. I usually use a very small straight screwdriver. In order to prevent the loss of the clip I try and surround the motor with a rag. You really don't want to lose circlip. Holding your thumb over the circuit what the prize it with a screwdriver, sometimes works. It's then reasonably easy to separate the two halves of the motor. Put the winding side away in a safe place, away from dirt and metal filings.
Next, must remove the grub screw from the top of the bell housing. It's only tiny, but it's the only thing that grips the shaft the bell housing. The friction between shafting the bell housing, is variable. You may find the shaft will literally push out with your thumb. In most cases it isn't that easy. In most cases of stainless steel shaft is pressed into the bell housing. The stainless steel gets very good grip on the aluminium. After a while this grip improves even more. So it takes something special to separate the two.
Aline the center-punch in the centre of the top of the shaft. Initially we want to make an indentation in the top of the shaft. The punch will quickly become blunt but that doesn't matter. Each time you press down on the center-punch, the shaft will move a tiny bit. In most cases, it takes about five minutes to push a shaft through the top of the bell housing. You have to be patient, sometimes it doesn't appear to be moving. Remember, it's the shock that does the work, not the force. Don't try to apply any more force that takes to set off the punch. You will succeed.
It's time to insert the new shaft. You have to be careful here, we could damage the shaft or the bell housing. I like to use tack hammer and piece of wood with a hole in it. Once the top of the shaft is protruding, it's time to replace the bottom of the motor. Continue to tap the shaft until the circlip groove is about a millimetre above the bottom of the motor. With the utmost care not to lose the circlip, replace it back on new shaft. A couple more taps on the shaft will be in place. Replace the grub screw and it will be done.