By "Jackshaft" do you mean the "spindle"?
Yes, it will turn, if you don't have it clamped in place by using some kind of tool or clamp to hold it from turning! A pair of Vise-grips, clamped onto the flange of the pulley (one edge, not both edges) should keep it from turning, if you place the clamping tool where it will stop agains something on the deck! (Gee, it is hard to explain in laymans language, especially by someone to whom it is second nature. e.g. a mechanic of 60 years experience.)
I wasn't born with a set of sockets in my hands, but learned a lot in the "College of hard knocks" and the trade school: "Learn by doing!" I say the preceding, only to explain the preceding statements, and so i don't receive condemnation from those who can't understand what i mean.