I need to replace the drive shaft on a home made 6.5 hp long tail. I can't use the one on it to measure because the prop end was extended. Question how long should the shaft extend past the lower bearing on prop end ? How much thread do I need for prop? How much space should be between the back of the prop to the rear bearing? Sorry for the novice questions . I need to replace the shaft so it will fit the 3/4 x 10 props. The engine side goes into u-joint so I can get that measurement just need prop end info so I can order new drive shaft.

1 inch past lower bearing, 3 inches of thread is what I have on my MB.

image.jpgThis is what I think I need as far as new drive shaft for 6.5 home made long tail. 17-4 shaft material. 3 1/2 inches of 3/4 by 10 thread on prop end. And u joint key on motor end . The outter housing is 42 inches. So overal length will be 48 inches. 7 by 4 mud prop? What do u all think ? Should I pull the trigger? Any advice would be appreciated. The motor is on 12.5 ft aluminum flat.

Have you bought this thing yet? Looking at the photo (and maybe it is deceiving) the shaft house looks to have not much in the way of support...That looks like something I would pass on buying, just to me looks like a good way to get stuck in the marsh... You are pretty close with your dimensions, we use 3/4" cold rolled steel round stock cut to length and machined just like you mentioned... Just remember its better to add another inch or so to the end (so you get some extra threads) and can get everything put together, That way everything will fit on the threaded end fo sho (jam nuts, prop and lock nut) and you can cut the little stump of threads off that you might not use. Better to have a little more you can lop off than to barely squeeze everything on ya know?

So you think I should go 4 inches of thread for prop and cut any excess off after I put prop on. ?

If your length is 48" buy 49" and use the extra inch for more threads if need be...

Im about done building mine right now and I ran 72" DS with 5" of threading just to be safe.