The Stanley 803 Hand Drill is known for jamming occasionally, some more than others. Paul mentions this too (in his book p.427-428). The problem is the pinions should only be meshing about 3/4 of their depth – any more and they can jam. I resolved this by inserting a thick steel washer onto the spindle before fitting the large pinion wheel. The teeth are now separated just the right amount, it works smoother than ever before, and never jams.
The 803 was designed for dismantling to fit in shallow toolbox drawers, but as I don’t need to take mine apart again, I also added a couple of serrated locking-washers. Stops it rattling and makes it more positive in use.
No prizes for engineering excellence, but I thought it worth sharing.