Dooing up a propellor nut ?

[Boo2]

Hi,

I am just about to re-fit the prop to Sunrunner's new shaft and I wondered if there's anything special I need to know ? It's a bronze folder on a keyed duplex stainless shaft and has a cylindrical bronze retaining nut with flats milled in the end to take a socket. Should I grease the shaft where the prop sits ? How tight can I do the nut before the taper will decline to release when I come to remove it next time ? Anything else I need to know ?

Thanks,

Boo2

 

[Rigger Mortice]

I would expect the prop manufacturer to supply all that information in particular the torque settings for the nut. Flexofold certainly have it on their site but you haven't said what make yours is.

 

[maxi]

Greasing the taper is not a good idea, over time the grease disappears & that leaves you with a very small but unwanted degree of play, where there should be no play.

 

[AndrewB]

As tight as you can, because there is a lot of pressure on the nut to encourage it to unwind, as I learnt to my cost many years ago. Since then I've used a castle nut, with a split-pin right through the shaft, to make sure it stays put. This is a common arrangement.

It's worth investing in a long spanner or a full-length torque wrench for this. Don't forget the shaft will have to be held against the force of doing up the nut. Putting the engine in gear for this purpose is dangerous, you could accidentally start the engine.

You don't really need to grease the shaft, as the prop will normally pop off easily enough when tapped with a mallet. The propeller key though can be trickier to get out. It may pay to cut a short horizontal slot in the outer end of the key, so in future it can be prised out with a screwdriver.

 

[LadyInBed]

How is the shaft keyed for the nut?
Is it D shaped to take a bend over washer or drilled through to take a split pin?

 

[Boo2]

How is the shaft keyed for the nut?
Is it D shaped to take a bend over washer or drilled through to take a split pin?

Neither, IIRC (it's on the boat) the shaft itself has no arrangement for keying the nut, but there is a threaded hole through the prop hub and also through the nut and a grub screw which screws through both to abut the shaft in the middle of the threaded length. This means that the prop hub will have to rotate with the nut as it is done up (to ensure the holes for the grub screw align in both hub and nut) or else a new hole is required after doing it all up. In either case I will have to bump a drill down the threaded hole to dimple the shaft thread before finally putting in the grub screw.

RM asked who made the prop and it's Elice Radice btw. There's a pic of the hub arrangement here :

Thanks for all the replies,

Boo2

 

[rob2]

No grease! In fact, you should thoroughly clean and degrease the taper on both shaft and propellor. It's true that the twio items can wring together, so that removal becomes difficult, but a hub puller applied to put the joint under strain and taps with a mallet to shock it will get it off. I had one stuck and left the puller on when it got dark... Next morning prop and puller were lying on the floor - I guess the cold that night was enough to break the joint through differential expansion.

Locking the nut to the prop will work as the key is being used to stop both prop and nut from turning, although I'd prefer a seperated system for each. The easiest is a castellated nut and pin. Generally the nut is tightened to the specified torque (or a little less) and then just a little more to align the nearest castellation to the hole and the pin is inserted. You can, of course, use some loctite on the thread to secure the nut which is not uncommon practice if a self locking nut is used.

Rob.

 

[NormanS]

I have never been able to understand why all propellers don't have tapped holes in their outward face to facilitate removal. All my several props have had this, and it saves all the bother of using heat, or bashing with hammers. All it needs is a suitable steel strongback, and appropriately threaded machine screws or studding.

 

[Plevier]

but there is a threaded hole through the prop hub and also through the nut and a grub screw which screws through both to abut the shaft in the middle of the threaded length. This means that the prop hub will have to rotate with the nut as it is done up

I can't follow that Mike.
You said the prop is keyed to the shaft so how can it rotate with the nut?
If you could turn the prop hub and the nut together, there would be nothing but the grubscrew stopping them undoing.

 

[Boo2]

I can't follow that Mike.
You said the prop is keyed to the shaft so how can it rotate with the nut?
If you could turn the prop hub and the nut together, there would be nothing but the grubscrew stopping them undoing.

Well you've got me :

The prop nut is prevented from undoing by a grub screw which locates on a dimple (not yet made) in the thread of the shaft. The hole in the prop hub through which that grub screw is accessed is also threaded and the grub screw is long enough that it engages the threads of nut and hub at the same time (the wall of the cylindrical nut is not very thick so I suppose that is why they've threaded both hub and nut).

But, as you point out, there is a shaft key between shaft and hub so the alignment of both the grub screw holes depends upon the start position of the thread on the shaft wrt the key location. And it's a new shaft so there is no chance the thread start/end will be in the same place as the old shaft so I guess I will have to do the nut up tight then drill a new hole through the nut, dimpling the shaft at the same time, and re-tap to fit the grub screw.

I think I may just give it back to the engineers to fit...

Boo2

 

[NormanS]

Surely if the grub screw (threaded in the prop boss) is screwed tightly into a dimple on the nut, that will suffice. Well, that's what my Bruntons Autoprop has.

 

[Rigger Mortice]

It's a bit surprising that the manufacturers don't seem to produce an installation guide but their UK agents http://www.sillette.co.uk/sillette_downloads_page.html also do the Gori prop which is similar. FWIW the Gori installation guide may be better than nothing.

 

[Plevier]

Surely if the grub screw (threaded in the prop boss) is screwed tightly into a dimple on the nut, that will suffice. Well, that's what my Bruntons Autoprop has.

That's definitely what is done here on Radice's 3 blade folder. http://www.elicheradice.com/linea58/download/Montaggio 3PABB.pdf

In fact looking again at Mike's link, surely that's how the 2 blade is done as well?

BTW there is a tightening torque for the retaining nut specified in the 3 blade instructions, 220+/-20Nm.

 

[Boo2]

Surely if the grub screw (threaded in the prop boss) is screwed tightly into a dimple on the nut, that will suffice. Well, that's what my Bruntons Autoprop has.

That's definitely what is done here on Radice's 3 blade folder. http://www.elicheradice.com/linea58/download/Montaggio 3PABB.pdf

In fact looking again at Mike's link, surely that's how the 2 blade is done as well?

Yes, but on mine the dimple on the nut is a threaded through hole, wonder why they've done that ? (see pic below) The new shaft will almost certainly need a new locking hole in the nut so I could just make a dimple this time...

BTW there is a tightening torque for the retaining nut specified in the 3 blade instructions, 220+/-20Nm.

Thanks for that.

Boo2

 

[Ruffles]

I can't follow that Mike.
You said the prop is keyed to the shaft so how can it rotate with the nut?
If you could turn the prop hub and the nut together, there would be nothing but the grubscrew stopping them undoing.

I suspect the key is a relatively loose fit in the key of the prop. So repeated forward and reverse could have the prop rotating a couple of degrees each way. Which could work the nut off over time.

A nice big spilt pin is very reassuring....

 

[Plevier]

Yes, but on mine the dimple on the nut is a threaded through hole, wonder why they've done that ? (see pic below) The new shaft will almost certainly need a new locking hole in the nut so I could just make a dimple this time...


Thanks for that.

Boo2

Mike
I can't believe that the grub screw is supposed to go through two threaded items not in contact with each other and then onto the shaft. That's lousy engineering.
That nut looks very rough work. Is it new?
Have they sent you the right one?
As Norman said , the way it's designed, it looks as though the grub screw should just go through the hub and then onto the nut, with or without a dimple. That's what the drawing looks like, Norman says that's how the Autoprop is done, and I can tell you that's how the Kiwiprop is done.
If the nut projected clear of the hub, I too would favour a split pin, but that's not practical here.
Mike

PS Fixed my aerial - badly assembled connector at the top shorting out. Two trips up the mast of about an hour and half an hour. Did not enjoy at all.