thread wear on prop shaft what is causing it?

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,417
Looks like your typical splined shaft that has been threaded.

What am I missing?
 

briangcc

Commander
Joined
Jul 10, 2012
Messages
2,090
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

Rear Admiral
Joined
Jul 22, 2008
Messages
4,222
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

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
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.
 
Top