Prop nuts

[cardude01]

The "lapping" compound is at NAPA as valve seating compound.

A good prop shop will have keys that are in 2 stepped sizes as well as oversized keys.

If the shaft key fit is tight , the prop folks will broach an oversized keyway , and provide a stepped key

Fairly easy to modify an oversized key by sliding the key along a file to get the exact fit.

Awesome. Thanks. I found a local prop shop. Going to take it to them today.

 

[fstbttms]

Useful to know the first nut is labeled the jam nut; I'd thought labeling was the other way around, second nut being the jam nut.

The thin nut is the "jam nut." The thick nut is the "king nut." The jam nut goes on first, next to the prop. The king nut goes on second. Amongst knowledgeable professionals, there is no debate about this, as was previously suggested.

 

[dhays]

Ummm... not sure I understand "thin nut first" relative to Cardude's pic....

In the pic, looks like the first nut is thicker than the second.

???

Also looks like the second is larger in "diameter" (?) than the first.

Useful to know the first nut is labeled the jam nut; I'd thought labeling was the other way around, second nut being the jam nut.

-Chris

I think the point is that the nuts on cardude's shaft were reversed from the order they should be.

 

[cafesport]

Dude, you may have opened a can of worms. A trip to a good prop shop is your best solution. A good prop shop will have the propscan software and should diagnose your wheel for free. The level of rebalancing and repair you need can then be assessed. You didn't mention whether you checked your cutlass bearing but with the boat already out of the water you might consider installing a new one now rather waiting to do it later. A sloppy fit like you have in that video can cause a number of other problems.

 

[ranger58sb]

I think the point is that the nuts on cardude's shaft were reversed from the order they should be.

Ah. That's what I thought from the pic... and from what he eventually said... but then thought folks were contradicting him...

So I got all wrapped around the axle.

-Chris

 

[rwidman]

The thin nut is the "jam nut." The thick nut is the "king nut." The jam nut goes on first, next to the prop. The king nut goes on second. Amongst knowledgeable professionals, there is no debate about this, as was previously suggested.

A bit of thread drift but since you would know; What about replacing a prop in the water. Obviously this can be done with the proper tools and experience, but what about the lapping to get a perfect fit?

My boat came with a spare prop but I have no way of knowing if it's ever been lapped to fit the shaft.

 

[fstbttms]

...what about the lapping (underwater) to get a perfect fit?

Unheard of, in my experience.

 

[rwidman]

Unheard of, in my experience.

So we just have it installed and see how it turns out? If it shakes, get it hauled and fitted properly.

 

[fstbttms]

So we just have it installed and see how it turns out? If it shakes, get it hauled and fitted properly.

I have 22+ years in this business and have installed many, many props underwater. Never even heard of "lapping" until somebody mentioned it years ago on some sailing forum or other. Have never had a customer ask me about it, never had a prop retailer talk about it, never had repair facility mention it, never heard of another diver discussing it- nothing. And no problems with any prop that I have ever installed that I am aware of.

 

[cardude01]

Update:

Got the prop off easily. Too easily maybe. Took off the jamb nut, and when I put the wrench on the nut against the prop it was barely tight. I was ready for a battle but I put the wrench on it and it moved very easily. Maybe that was my issue?

I removed the prop and looked at the keyway in the shaft-- it fits in there tightly. They key fits less tightly in the prop hub. Taking the prop to a shop to let them look.

I did the fit without the key and made a mark on the shaft like David suggested. I just barely tightened the nut on the prop and could hardly get the prop back off. Had to tap on the hub with a plastic hammer to get it loose. So the hub seems to fight tightly on the shaft.

How tight should that nut be on the prop? How many turns after it makes contact with the hub?

 

[fstbttms]

How tight should that nut be on the prop?

As tight as you can get it with a big wrench. Both nuts. Run a length of lumber (I use a piece of 2X2) between the keel and the rudder to immobilize the prop. Then really torque those nuts down.

 

[cardude01]

As tight as you can get it with a big wrench. Both nuts. Run a length of lumber (I use a piece of 2X2) between the keel and the rudder to immobilize the prop. Then really torque those nuts down.

OK thanks a lot. Problem is all I have is a big crescent wrench at this point. I need to get a better tool. The nut is a weird size. 46 mm.

 

[fstbttms]

Problem is all I have is a big crescent wrench at this point. I need to get a better tool.

I find that an 18" pipe wrench does the job. You can slide a length of pipe over the handle to make a cheater bar if you like.

 

[cardude01]

I find that an 18" pipe wrench does the job.

Just a regular old pipe wrench? I've got those. So I shouldn't worry if it gouges that nut a little bit? The nut is stainless so maybe it will hold up OK.

I told my wife today that I need to find a job and a good boat yard for a few months so I can learn some of this stuff. [emoji23]

 

[fstbttms]

So I shouldn't worry if it gouges that nut a little bit?

It's a hunk of metal that lives underwater, for God's sake. Does it have to be pretty?

 

[Bacchus]

Note... After tightening the small nut - You should beholding the small nut while tightening the large nut against the small

 

[Northern Spy]

You want to make sure that the fit isn't riding on the key as well. Take the prop off again and put the key back into the keyway. Reinstall the prop and check that it goes back to the mark.

Make sure the key is not bottoming out at the radius at the end of the keyway, which will force the hub off center and create a stress riser on the shaft at the keyway.

 

[cardude01]

You want to make sure that the fit isn't riding on the key as well. Take the prop off again and put the key back into the keyway. Reinstall the prop and check that it goes back to the mark.

Make sure the key is not bottoming out at the radius at the end of the keyway, which will force the hub off center and create a stress riser on the shaft at the keyway.

Ok. Thanks.

So I took the prop to a prop shop that does mostly shrimp boat's and some offshore boats, and he said my key had a little wear but the key/keyway fit in the hub seemed OK.

He then said make sure you install the prop with the big nut against the prop. [emoji41]

 

[Northern Spy]

Everywhere I have worked, it would be considered very bad practice, unprofessional even, to use a pipe wrench on a nut. A smooth jaw wrench (aka Ford wrench) or smooth jaw hex wrench (looks kind of like a pipe wrench) is the proper adjustable tool to use. I have a huge crescent wrench as well, but the jaws get too thick to be used. I use a Ford wrench.

 

[fstbttms]

Everywhere I have worked, it would be considered very bad practice, unprofessional even, to use a pipe wrench on a nut.

You have never worked underwater. I assure you it is common practice.

 

[Northern Spy]

Torque? Tight. As tight as you can get it using hand tools properly. Probably not a calculated specification. I don't recall finding one in SAE J755 or in P-6. In a typical bolted joint, the threads are used to lengthen the fastener to create a tensile spring. That value is based on tensile strength of the bolt and can be easily calculated. In this case, threads and nut are only used to drive the prop up on the taper and hold it there.

 

[Nomad Willy]

A lot of things are "common practice" that I do'nt do. I would'nt put a pipe wrench to a machine nut either.

It's common practice to remove a prop by backing off the prop nut about 1/16", installing the puller tight and then hit the end of the prop shaft w a big hammer .. and of course the prop pops off against the nut.

I never do it that way. I install my prop puller and make it tight w the the prop nut just slightly loose and heat the prop hub w a MAP torch rotating the prop by the blades frequently until the prop goes bang. It's quite violent. And it's done. Beating on the end of my prop shaft and hence the thrust bearing in the transmission is not an option for me. But I'm fussy.
A propane torch will work but it takes a lot of time and even the blades get quite warm. The hotter MAP torch is hot enough to do the job quickly and only heat the prop hub.

Speaking of fussy I put the prop on w/o the key and check the fit. One can tell if it is'nt flush by eye or handling if it's way off but pushing the prop on very lightly and rotating it a few turns will make very fine but visable scratches at 90 degrees to the shaft where the shaft is against the 10 degree bore in the prop. If it's off the scratches will be only at one end. If so I take the prop and shaft back to the shop to get an accurate kiss pass on the lathe or a good reamer. And a test in the shop.
Lapping is time consuming and only fixes very slight variations.

 

[Northern Spy]

You have never worked underwater. I assure you it is common practice.

I laughed. I used to work with divers all the time. I get it. Just because it is a common practice, doesn't make it correct.

But really. Get the right tool if you make your living at it. No excuses. Don't take it personal. Consider it a step up against your competition.

https://www.acklandsgrainger.com/en/product/WRENCH-HEX-STRAIGHT-25-20IN/_/R-RDG31280

 

[RT Firefly]

Greetings,
Mr. 01. "...could hardly get the prop back off." I don't know if I'm right or wrong but "jamming" on with little pressure suggests to me that it the prop and shaft could benefit with a bit of lapping. Might be hanging up on a high spot along the taper and just seem to be a tight fit.

 

[Northern Spy]

Greetings,
Mr. 01. "...could hardly get the prop back off." I don't know if I'm right or wrong but "jamming" on with little pressure suggests to me that it the prop and shaft could benefit with a bit of lapping. Might be hanging up on a high spot along the taper and just seem to be a tight fit.

Usually if you can't get it off it means the taper is spot on.

 

[cardude01]

That's what I was hoping!

 

[fstbttms]

I laughed. I used to work with divers all the time. I get it. Just because it is a common practice, doesn't make it correct.

But really. Get the right tool if you make your living at it. No excuses. Don't take it personal. Consider it a step up against your competition.

https://www.acklandsgrainger.com/en/product/WRENCH-HEX-STRAIGHT-25-20IN/_/R-RDG31280

 

[RT Firefly]

Greetings,
Mr. NS. Thanks for the correction.

 

[rwidman]

.................... I install my prop puller and make it tight w the the prop nut 1/32" back and heat the prop hub w a MAP torch rotating the prop by the blades frequently until the prop goes pop .. ........... .

That's really hard to do if the boat is in the water.


I agree with you though that banging on the prop shaft with a big hammer could possibly damage the transmission and should be avoided if possible.

 

[Ski in NC]

The only way to end the big nut/small nut issue would be to make them both the same size.

And I don't see a big issue with using a pipe wrench on the nuts. A bit of rash on the flats?? No big deal.