Need Help: Prop Shaft Jam Nut Won’t Budge

[testingthewaters91]

I am not sure that they are Incorrect.
I understand that the larger nut is the primary one. It is tightened to the torque spec, which often means tight (really grunt tight) to most Boat Marine Workers (compared to BMWs, as they charge about the same).

The smaller nut is the locking nut.

Maybe I'll just leave them on, but I thought of changing them after reading this:

The Truth About Prop Nuts - And Why the Half Nut Goes on First — FollowingSeas

There are many boat owners, mechanics, and yard workers who do not install propellers properly. Here is what they should do and why it matters.

www.followingseas.media

I thought it would be an easy switch though. I don't even know how I would torque them down to spec by hand.

 

[jssailem]

I had not read that before. It makes logical sense.
I can understand the mechanics being discussed. Further confirmation of this approach is worth exploring.

 

[jssailem]

I found the following information, which supports the idea of using the thin nut first and the large nut as a locking nut.

The Use of Two Nuts to Prevent Self Loosening of Fasteners

Thanks for helping me rethink the stuff I have always heard that appears to be WRONG.

Check out this graph of the bolt preload kN when exposed to vibration cycle fatigue testing.

 

[testingthewaters91]

I found the following information, which supports the idea of using the thin nut first and the large nut as a locking nut.

The Use of Two Nuts to Prevent Self Loosening of Fasteners

Thanks for helping me rethink the stuff I have always heard that appears to be WRONG.

Thank you for finding that wonderful read. I'll add it to the collection. This now brings me to the issue of how to get them off, back on, and properly torqued without damaging them.

I'm all ears on methods because this thing is extremely tough to remove! I'll try and impact if the hand tools fail. Also wondering if anyone has any idea about torque specs.

We're all in this together to make ourselves as safe as possible out on the water.

 

[jssailem]

You got more going on than the tests show on new bolts and nuts.
There is saltwater corrosion. There is likely fastener galling of the nuts and shaft.
You may break the current nuts loose only to replace the prop shaft and locate new nuts to fasten the prop more correctly.

That is something to consider.
If you want to replace the prop and prop shaft, then it is a no-brainer. Rip off the old and start with new and better.
If you want to leave them for a season and check on them next year, then you at least have a base point for comparison. Perhaps 80% is good enough.

 

[testingthewaters91]

You got more going on than the tests show on new bolts and nuts.
There is saltwater corrosion. There is likely fastener galling of the nuts and shaft.
You may break the current nuts loose only to replace the prop shaft and locate new nuts to fasten the prop more correctly.

That is something to consider.
If you want to replace the prop and prop shaft, then it is a no-brainer. Rip off the old and start with new and better.
If you want to leave them for a season and check on them next year, then you at least have a base point for comparison.

So this prop (and likely prop shaft) was installed about three years ago when a new Yanmar 2gm20f was installed and are in great condition. What do you recommend? Thoughts?

Leave as is? Replace the nuts? Risk damaging the shaft during removal?

 

[testingthewaters91]

One of the tricky aspects I'm dealing with is that the prop shaft rotates when I put pressure on the nut, so I've been trying to grab the other nut with pliers to keep it from rotating.

There must be a better way.

 

[capta]

I would first remove all of the old bottom paint from the crevices around the nuts and then try squirting in some penetrating oil like pb blaster.

PB Blaster and WD-40 do not help on yellow metals.

 

[testingthewaters91]

PB Blaster and WD-40 do not help on yellow metals.

This is what I originally thought, but it was highly recommended.

 

[capta]

Small grinder with a cut off disc.
Carefully!!
Gary

Just a torch. Please, no grinding, cutting, or penetrating oils.

 

[testingthewaters91]

Just a torch. Please, no grinding, cutting, or penetrating oils.

I was thinking of using my heat gun instead of a torch.

I also am not sure what size these nuts are. I could get combination wrenches that fit the proper size.

 

[BigEasy]

Use a combination of large wood blocks (like the ones used to support the keel) & a smaller piece (like a 2 x 4) to engage one of the propeller blades (close to the hub) to prevent the prop & shaft from rotating. Pliers will not work. Purchase the specific size wrench for the stubborn nut; if that doesn’t work, use a cheater bar. Try an impact wrench, again with the prop blocked. If it still doesn’t budge, I would leave it be. No need to cut & section the nuts, at this time, just to reinstall new ones with proper orientation. “If it ain’t broken, don’t fix it!”

 

[capta]

I think Don is thinking you are pulling the prop off…."hence the gear puller."

I would try 2 pipe wrenches if you can get one on the thin nut…and as others have said, try to clean the paint off the treads, and use some penetrating oil. You can certainly try heat as well.

Greg

Usually, if the nut is secure on the threads, the only safe way to release the nut and prop, is with heat. Even with a puller, heat simplifies the prop removal operation. It is not a good idea to use steel tools on bronze, or brass, though brass shouldn't be found around seawater.

 

[testingthewaters91]

Usually, if the nut is secure on the threads, the only safe way to release the nut and prop, is with heat. Even with a puller, heat simplifies the prop removal operation. It is not a good idea to use steel tools on bronze, or brass, though brass shouldn't be found around seawater.

Funny you say that, because my boat had bronze ball valves on brass thru hulls from PO.

 

[Tally Ho]

So this prop (and likely prop shaft) was installed about three years ago when a new Yanmar 2gm20f was installed and are in great condition. What do you recommend? Thoughts?

Leave as is? Replace the nuts? Risk damaging the shaft during removal?

Leave it be until you HAVE to take the prop off.

I used to have mine on backwards….’cause I didn’t know any better. Never had a problem. Now using a MaxProp that uses a different type of shaft nut.

But if you can’t get them off, and if the cotter key is secure, it isn’t going anywhere.

There must be more important things to worry about on this good old boat

Greg

 

[LLoyd B]

Well I didn't know all that and thank you for the new information although I'm not sure I'm totally convinced. But now I think I'm going to check and see if the Snap on catalog has a torque pipe wrench.

 

[testingthewaters91]

Leave it be until you HAVE to take the prop off.

I used to have mine on backwards….’cause I didn’t know any better. Never had a problem. Now using a MaxProp that uses a different type of shaft nut.

But if you can’t get them off, and if the cotter key is secure, it isn’t going anywhere.

There must be more important things to worry about on this good old boat

Greg

My rational was that it's already out of the water so I might as well make it right. I guess I could try a breaker bar and a proper deep socket with MAPP gas... Honestly, this is all a large part of the fun!

 

[testingthewaters91]

Well I didn't know all that and thank you for the new information although I'm not sure I'm totally convinced. But now I think I'm going to check and see if the Snap on catalog has a torque pipe wrench.

You're welcome. Why are you not convinced? And what is a Snap On Catalog? I've never heard of it before.

 

[kappykaplan]

And what is a Snap On Catalog

Snap On sells sockets, wrenches, etc.

 

[dlochner]

But now I think I'm going to check and see if the Snap on catalog has a torque pipe wrench.

A pipe wrench is not a good tool for this job. A pipe wrench grips pipes with the teeth on the jaws, this will severely damage the soft bronze prop nuts. There are "pipe wrenches" with flat jaws which will work.

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