Help with Propshaft Nut (forward end)

[NahanniV]

My boat is built in Finland. Some great workmanship, but they do things a bit different than in North America:

I'm working on replacing the hose between my stern-tube and stuffing box, but have run into an odd nut on the forward end of the prop-shaft. It's inside the shaft coupling.

I have been searching the internet for a socket to fit this nut, but the best I have found is some pictures of homemade sockets for similar nuts.

I once had a similar nut on a Vetus flexible coupling, but the tool was a wrench that would not fit this application (inside the coupling).
They called it a slotted lock nut (DIN 1804).

Anybody know another name of this type of nut ?
Is it a standard ? Or custom ?
Where can I get a socket ?

Please see attached picture and sketch.

[Zach]

That is called a spanner nut.

The critter you are after, looks like this:

40mm Spanner Socket for Mercedes Lock Nut Drive Pinion Shaft Most Models 68 93 | eBay

A spanner nut socket.

[Zach]

Where to buy a replacement...

J.W. Winco, Inc. - Slotted Spanner Nuts

Most of the time when I come across those, I end up having to take a cold chisel and cracking the nut, and a round drift to loosen them. Once you have a new nut that matches the thread pitch, you can normally buy the right socket to match it from the seller.

Sadly, a traditional hook spanner wrench normally isn't up to the task to loosen them up after they've been around for a while.

Zach

[delmarrey]

You can use a spanner wrench too if you can get it in there.

[NahanniV]

This is a better picture of the nut I'm trying to loosen and the tool that I need to get at it.

However, I have not been able to find the correct size tool; Needs to be 40mm across the flats of the indents. (D3 in the diagram of the nut) the B dimension is 5mm.

[delmarrey]

Originally Posted by NahanniV

This is a better picture of the nut I'm trying to loosen and the tool that I need to get at it.

However, I have not been able to find the correct size tool; Needs to be 40mm across the flats of the indents. (D3 in the diagram of the nut) the B dimension is 5mm.

Actually the d3 is the face diameter, not the flats. But it looks like a KM6 in this chart>>> J.W. Winco, Inc. - Metric Size, Bearing Lock Nuts
What is your shaft diameter. Bearing nuts are standardized so they should be all the same.

There is also this chart>>> http://www.skf.com/files/100000.pdf

And here are their wrenches>>> SKF Axial lock nut sockets TMFS and TMFS N series
Or here>>> Locknut sockets - LOCKNUT-SOCKET
And some more good info>>> http://www.basco.com.pe/pdf/fag/fag_...ounting_us.pdf

This should keep you busy for awhile.

[NahanniV]

Thanks for the help !

The shaft diameter is 35mm.

I'm not able to directly measure the outside diameter of the lock-nut since my calipers will not fit into the space.

I think you are correct that it is the KM6

The cheapest SKF socket (that I can find) to fit:
SKF Axial Lock Nut Sockets TMFS Series | Spanner Sockets | IndustrAlign
$223. !

Local bearing company says 2-3weeks $300. !

There is one a little cheaper in England on E-Bay, but not much cheaper after duties and taxes.

I don't expect to do this job again, so hard to justify the cost.
Unless I can borrow one, or someone can point me to a cheaper option, I will have to try and make one.

[JeffBurright]

We had our lock nut fall out of our transmission earlier this year, and I was able to make a wrench out of a short piece of pipe to screw a new lock on. Just cut and/or file notches in the pipe so it fits into the slots of the nut snugly, then cut a notch or hole in the other end of the pipe that you can stick a screwdriver or other pry bar through to crank the nut. Our blog has a picture of the first prototype socket I made out of PVC for a better idea of what I'm talking about. The PVC actually worked pretty well, so it might be enough depending on how tight your nut is.

Be aware though that usually the nuts have been "keyed in" with a cold chisel to prevent them coming unscrewed easily. You might have to grind or chisel out the keyed section of the nut first.

Awww, nuts (and couplings)

Good luck!

[delmarrey]

Originally Posted by JeffBurright

We had our lock nut fall out of our transmission earlier this year, and I was able to make a wrench out of a short piece of pipe to screw a new lock on. Just cut and/or file notches in the pipe so it fits into the slots of the nut snugly, then cut a notch or hole in the other end of the pipe that you can stick a screwdriver or other pry bar through to crank the nut. Our blog has a picture of the first prototype socket I made out of PVC for a better idea of what I'm talking about. The PVC actually worked pretty well, so it might be enough depending on how tight your nut is.

Be aware though that usually the nuts have been "keyed in" with a cold chisel to prevent them coming unscrewed easily. You might have to grind or chisel out the keyed section of the nut first.

Awww, nuts (and couplings)

Good luck!

If the nut has a lip like what's in your posted link, then yes, the lip needs to be bent to get it on/off. Otherwise for standard nuts, if there is a keyway in the shaft, there there is a lock washer that goes behind the nut like on page 19 of this link>>> http://www.skf.com/files/100000.pdf

The problem with using a pipe is it needs to be just the right diameter. I've made a lot in my shop for one time use but if they're going to be used over and over they need to be heat treated. Pipe material is fairly soft for real stresses.

[JeffBurright]

We were lucky that I had a bit of metal pipe onboard close to the diameter of the lock nut and I could bend the flanges out a hair to fit the slots in the nut. The final socket design was only about 3 -4 inches long. I agree with you though that it was a not a durable tool, just a one-off. In my opinion, its worth the hour of creating the tool to see if it saves the OP a few hundred bucks.