Spatial reasoning is absolutely a form of reasoning (it's right there in the name!). I don't have any references handy, but I've read a few accounts of musical and math prodigies who have a form of synesthesia that allows them to "see" notes and numbers, respectively, which allows one to reason about abstract concepts as easily as you or I could spot the difference between a circle and a square. Very interesting stuff.

I think it is. The actual process of comprehending a crankshaft uses conscious thought as a conduit to transfer the idea into memory.

However, I think lotsofmangos in the Feynman quote was referring to the process of visualizing a crankshaft, which is most definitely conscious thought. Visualization is often not language in the mind.

Visualization is language, but of a different kind. Take those who are born deaf and think in signs.