thread wear on prop shaft what is causing it?

[ratbag]

 

[jimmbo]

Improper Torque on the Prop Nut?

 

[dingbat]

Looks like your typical splined shaft that has been threaded.

What am I missing?

 

[briangcc]

Top of the thread, from what I can see, looks OK. Bottom of the thread, towards the plain splines, looks like they're ground down. Hit something??

 

[airshot]

I believe the thread is deeper at the beginning and gets more shallow as it gets closer to the straight spline area. That is what I am seeing in your pic. Threading tools have a taper on the lead in, so when it threads that shaft, the leading edge with the taper is where the thread runs out.

 

[Texasmark]

Looking on the non threaded spline, left side I think I see a grayish discoloration at a 30-45* angle. Considering the angle where engine/outdrives are position when sitting in a slip in a marina, I'd suspect some sort of corrosion (worn out sacrificial Zinc Anodes) besides the obvious runout of the prop nut threads, from where the MIL quit cutting.

 

[QBhoy]

Looks pretty normal to me perhaps.