Jam Nuts

[Ex-Calif]

FWIW - I agree with Gord and Dr. Calvert.

However, do not confuse jam nuts with lock nuts.

There are many types of locking nut - castellated, nylon inserted etc. but I am talking about things like nylocks where the locking nut definitely goes on last...

There are also nut "systems" where two nuts are purchased and installed as a pair. In these cases follow the instructions.

[sdowney717]

I think I would put the thick nut on first, torque it tight to set the prop on the shaft. then remove the thick nut and put on the thin nut torque it down, followed by the thick nut. Reason being I would want the prop pulled into shaft with as many threads as possible likely cause I would be worried about it stripping. I would also grease the threads and the shaft where the prop sits on shaft. Do you grease this or install it dry?

[micah719]

The thin nut first makes sense, but not intuitively. It even works with my car's steering wheel: the thickest nut on the whole car is last in behind that , and I've never had the wheel fall off!

Hmmm, I wonder what other things we've been getting wrong just because "that's the way everyone does it and always has......."

[GordMay]

Originally Posted by sdowney717

I think I would put the thick nut on first, torque it tight to set the prop on the shaft. then remove the thick nut and put on the thin nut torque it down, followed by the thick nut ...

Indeed.

In accordance with ABYC standard P-6 and SAE standard J755 (and virtually every other knowledgeable authority), the thinner (Jam) nut should be installed against the propeller (load), and the thicker (Plain) nut should be installed against the thinner nut with the cotter pin installed last.

Read Dave Gerr ➥ Boating Tip Of The Month

And Page 260 ➥ Boatinfo - Boat mechanical book

Or ➥ The Nature of Boats: Insights and Esoterica for the Nautically Obsessed - Dave Gerr - Google Books

[fstbttms]

Originally Posted by sdowney717

I would also grease the threads and the shaft where the prop sits on shaft. Do you grease this or install it dry?

You should never grease either the shaft, prop or nuts. The prop-to-shaft tolerances are so fine that adding a layer of grease means the prop may not seat properly. In addition, you do not want these part to be easily removed. You want them to want to stay in place. When it comes time to remove them, the proper tools will make short work of it, even if they've been installed dry. Why would you intentionally facilitate the prop moving around or the nuts backing off easily?

[sdowney717]

So no antiseize either.
That is fine, I have seen a yard worker struggling to remove stuck props on a shaft with a massive puller. They were stuck well on.

I think if it were me, I would heat the prop up to help.