I spent ages looking for the axle the flycranks are attached to, before realising the great bit piece of brass rod was it. I'm not sure why we need enough for a 7mm scale chassis, but that's what's supplied.
No matter. It's a very nice 3mm diameter - the same as the axles used for the wheels.
The holes in the cranks are undersized, which is far better than oversized, and need to be opened out using a set of large broaches. These aren't cheap tools, but pretty much essential for this job. Trying to use either a file or a drill for this job is likely to result in an oval hole in the wrong place (OK, drill in a pillar drill properly held will probably be OK, but if you can do this, you'll own broaches).
I enlarged the hole to 3mm and then opened it up a couple of twists with the tapered reamer. Then the axle and crank were put in the vice and it used as a press to force them together. No need for solder or Loctite here! It won't be moving on the axle either, or at least I hope not.
All this takes time, but I hope to get that back with minimal fiddling to fit this thing in the chassis.