MK1 prop shaft packing

Mine has a stuffing box that uses a single large nut that tightens over the threaded tube, plus a lock nut. I removed the nut to get to the packing material and now I can't reinstall it. It starts but only turns 1/4 turn and stops. It stops like it is tightened right up but I can't believe it is. I suspect it is more like it is trying to cross-thread. When I first removed this nut it turned about three or four full revolutions before coming free. So it seems to me the ID of the nut is coming in contact with the prop shaft and making it want to cross-thread. I've been very careful to not let that happen. I turned the lock nut all the way to the end to verify nothing is cross-threaded. Should I loosen the hose on the stuffing box to allowing it to create some slop, then install the nut and then re-tighten the hose? Or will this cause more grief?

Do you have a photo?

Do you mean it only will tighten a quarter turn after you've repacked it? Take out a turn of packing & see if it threads on farther. When it catches, squeeze the packing by tightening & then add more turns of packing after they've been compressed.

Greetings,
Mr. t. I would be hesitant to loosen the hose on the stuffing box if the boat is in the water.

Thank you for the responses. I can feel that I have pushed the packing material about 1/2" into the packing nut. So it apparently is not preventing the nut from turning. Also, it doesn't feel like the nut is hitting something soft. The boat is out of the water. It seems something is a little out of alignment. Loosening the stuffing box hose, or maybe loosen the midship bearing. The hose seems easier.

Cross-threaded

It sure acts like it's cross-threaded. Took all the packing out. The packing nut can now wobble all around to fit a slight miss-alignment if there is one, which I don't think there is. It still just turns 1/4 turn onto the threaded sleeve and then stops. Now to determine if there is way to the cross-threaded area and then try to remedy it.

I'm assuming you've wire-
brushed the threads already. There is a thread file made that you could use to clean up the outside threads but if the inside threads are messed up its going to be a pain. Have you run the jam nut all the way out over the threads. Maybe it'll clean them up some if you do that.

brushing the threads

I used a wire brush on as much of the sleeve as possible. For the packing nut I have ordered a 5/8" dia brass wire cylindrical brush with hex end. I will insert this into a hex extension I have chucked into a drill motor. Then I will clean up the female end and see if this does anything for it. Using a flash light and a mirror and looking inside, I see there might be some kind of crud in there. That would be better than cross-threaded. I have run the lock nut all the way off and re-installed it. Threads on just right. I have a thread file but I doubt it will help my situation. Thank you for the ideas.

Problem solved

After trying many other ideas without success, I ground down the first two threads inside the packing nut using a tapered stone in my Dremel motor. This solved the problem. There is still plenty of thread remaining.