Wren ... doesn't know what to think. While a clever fellow, well-read in a variety of subjects, it turns out that Wren has no grounding in engineering beyond the most basic everyday concepts. It is Zauberei who ends up being a good engineering assistant to Marius.

While most of the mechanism is behind the wall, Marius and Zauberei's check at the lever shows there is no resistance ... as there is no load. And they determine that it is because the Harrowstone fire ... while keeping the northern block mostly clear ... made it own to the southern block and melted/ destroyed the winch and chain mechanism. There is no way to get to it, to feed a chain through properly if you had one of your own, or otherwise repair the portcullis without a major undertaking beyond the scope of simple dungeon exploration.