I keep breaking set screws in prop shaft coupling

[FPNC]

Change to a clamp style coupling.

[sailah]

If you're in RI take a drive up to the Cape and see Keith Fenner at Turnwright Machine Works. His specialty is marine shafting and he'll make sure your shaft, prop and coupling are properly fit and faced, shaft straight with no runout, prop lapped to shaft, set screws dimpled, keyway properly fit etc.

He's done work for me and I've always been happy with the craftsmanship.

https://turnwrightmachineworks.com/

[phorvati]

Thank you sailah. I just talked to him. I think I am screwed a bit. Here are pics of the hole thing out of the boat. If anyone has a suggestion I would appreciate it.

Some of my issues.
1. My engine is already hitting the floor so I cannot bring it up. Flywheel housing is 1/2" from hull so I cannot bring it down either.

2. PSS is so tightly compressed, in the future, i cannot do anything without taking the boat out of the water and pulling the shaft out.

3. No support on the entire transmission and downangle drive. the whole thing is mounted off of flywheel housing, see pics. I might glass in something.

4. My straight bore coupling was too lose casuing key to shear and set screws to break. Now i need a new shaft and coupling. I am leaning towards split coupling.

[phorvati]

I just thought about it some more, I could move the engine forward to make room for PSS bellow. if my down-angle was 8 degrees, based on my trig, if i move engine forward 3", I would also need to go up just under 1/2"(0.417") to get to the same angle of shaft log. 3" would buy me a lot of room down there and i might consider keeping the current setup. I would need to lift the floor 1/2" as I am already hitting it.

[GRIT]

ZF 25 A is 8 degree down angle, and will handle 90hp without issue. It is rated Continuous duty at 74hp, and medium duty at 157 hp. It's also shorter than what you have there, so perhaps will give you more room for the pss, etc. Actually, to the best of my knowledge, all ZF transmissions, with down angle, are 8 degrees.

Where is that universal joint mounted? Is the engine flywheel housing exactly vertical?

https://www.performancediesel.com/wp...oads/ZF25A.pdf

Good luck.
Paul.

[phorvati]

Originally Posted by GRIT

ZF 25 A is 8 degree down angle, and will handle 90hp without issue. It is rated Continuous duty at 74hp, and medium duty at 157 hp. It's also shorter than what you have there, so perhaps will give you more room for the pss, etc. Actually, to the best of my knowledge, all ZF transmissions, with down angle, are 8 degrees.

Where is that universal joint mounted? Is the engine flywheel housing exactly vertical?

https://www.performancediesel.com/wp...oads/ZF25A.pdf

Good luck.
Paul.

its vertical. Its mounted on that plate that has isolation bushings

[GRIT]

Ok, if it's vertical, you'd need an extra 2 degrees, as you mentioned on your trigonometry post.

You're making progress though, it's all out and ready for your redesign.

Cheers, and good luck.
Paul.

[Kastaway]

I assume that the set screws are not subject to any thrust forces ?. An accurate keyway, coupler and alignment should isolate the set screws from resisting any torque loads, I just wondered if you had eliminated the possibility of any axial forces.