Some great ideas out there to make old better than new! Thanks for the good info!
I know this is an old (2008) post. But my question is; can you remove the old magnet without disassembling the motor (and risking dealing with the bbs)? You imply as much by saying " I would recommend putting the magnet in after you've re-assembled the motor, since the BBs are slightly magnetic".
In any event..I note that 1mm bbs are available on the internet with either magnetic (steel) or non-magnetic (Tungsten Carbide) versions for fairly cheap.
The motor's assembled pretty tight. You might be able to get the original magnet out without disassembling, but it was almost easier to deal with the ball bearings. Assembling the motor without the magnet and putting it in last allowed me to get the BBs in place a lot easier, and then I could slip the magnet in.
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Over the past few years I have upgraded about 25 Hobbytown drive flywheel drive chassis with DC70 motors using the neodymium magnets from K&J. This is a very easy improvement that is worth time and money. It takes about 1/2 hour of time and about 2.00 for the magnets. The result is about 2 tenths of an amp drop in current from 6 tenths down to 4 tenths on average. I get more power, extremely good slow speed and much better speed control over the entire speed range.I used a stack of 1/2x1/4x1/8 magnets. If there is an air gap I have read that it is best to fill it .I use old xacto blades. break them with pliers and use the end that mounts in the handle. If you place the stack in and the motor runs in the wrong direction just flip the stack over to make it right. I started with the N42 magnets and then tried N52 I am not sure if I have noticed any apparent difference. I also did a couple of the smaller DC60? motors on the Hobbytown switcher drives and feel there are similar performance improvements. Of course the Hobbytown are outstanding drives and these improvements make them better.
I have a few more DC70 powered drives to do . I also have a couple of older nonflywheel drive Hobbytowns to do at some point,it will be interesting to see how these conversions do.
Ron High