The spike is just round bricks stacked inside & between the cars.
So no drilling involved (I don't do that to Lego parts), but also the reason why that construction was a little fragile.
Especially for the cars not aligned to a 90° angle: these were secured just by 1 stud:
https://brickset.com/parts/4565393/plate-2x2-w-1-knob
instead of 4 for the other plates/bricks that I used:
https://brickset.com/parts/4211475/plate-2x2-round