He isn't that hard to kill (he doesn't have a load of HP).
He will spawn four A Miniature Steamwork. They are mezzable and a low HP (easy to kill).
I have read he may spawn more thna one wave of them, however, having done this twice now, I can tell you that if you mezz them and take out Gearwhir, you will only see four of them.
He drops six of the task items.
Edited, Sep 26th 2008 10:39am by GOMN