Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: BlueWotsit on October 15, 2010, 09:08:21 AM

Title: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 09:08:21 AM
A tugboat Im working on has a moveable Kort Nozzle with rudder blade inside, and the prop is fixed just behind the Nozzle, just enough room normally to unscrew the prop and let it drop down.

I need to change the brass prop but its stuck well and truly.

Normally with such a problem, I would drop the Kort down / dismantle it,  and then pull the whole prop shaft out to work on the prop outside the boat, however the Kort is well and truly embedded and refuses to drop as well, although the steering aspect of it is fine.

Any tips on removing the prop whilst still in situ ?


thanks
Andrew
Title: Re: Removing a brass prop problem
Post by: Shipmate60 on October 15, 2010, 09:37:24 AM
Andrew,
If you have a large soldering iron you could warm the prop.
Can you hold the shaft from inside the hull?

Bob
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 09:43:42 AM
Hi Bob

Theres about 4 inches of outer shaft I can get to inside the hull, upper part only though as underneath in its entirety its been filled in with car filler by the look of it.

The universal connectors on the inner drive shaft is pretty tight as well, wondering what it was stuck with, seems far to rigid for loctite .....makes you wonder doesnt it

What do you deem a large soldering iron, mines pretty basic but its got one of those thermostatic controls where I can regulate the temperature

Of course the eternal problem with a brass prop is the blade is quite sharp to hold even with cloth around it, and not much room to play with

cheers
Andrew
Title: Re: Removing a brass prop problem
Post by: Shipmate60 on October 15, 2010, 09:50:58 AM
Its the volume of metal that will transfer the heat I think mine is about 60 Watt.
If you can grip the inner shaft even with something like a tap key (Tap for thread cutting) and a decent pair of long nose pliears might give you some decent grip.
I assume you cant pull the shaft through the Kort then.

Bob
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 09:58:10 AM
Hi Bob

Will give that a try, with the Universal Connector being so tight, I wonder if heating the prop end, and then using a spanner to hold the inner end of the shaft might work. If not I will try holding the inner shaft as suggested.

With the prop on it cannot pass through or around the Kort at all as theres a fixed rudder blade inside the Kort which gets in the way, once the prop is off, then no problem

Will let you know later today how things pan out

cheers for the help
Andrew
Title: Re: Removing a brass prop problem
Post by: derekwarner on October 15, 2010, 12:02:30 PM
Andrew.....post a few photographs.........keep the soldering iron away  %%....you will only burn your fingers....... <:(  ...Derek
Title: Re: Removing a brass prop problem
Post by: Circlip on October 15, 2010, 03:46:43 PM
Sadly (as far as plastic is concerned) Bob is going in the right direction with the soldering iron to expand the brass prop on the shaft. Other way is more drastic and means cutting the prop off the shaft, same with the U/J and reshafting/proping/U/J-ing.

 If the existing shaft is still  shiney, it may be stainless, if rusty at all, break out the Dremel.

  Regards  Ian.
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 07:19:55 PM
Success !!!!!!!!!!!!!!

Applying heat to the back edge of the prop, where there was a locknut and suddenly it gave ............. brilliant thanks to all.


Next question directly relevant here :

The motor is a 720BB Torque Graupner

The tug is about 18 inches long.

Had to remove the original prop as whoever built it had not completely aligned the Kort nozzle straight and it was fouling when turning in one direction.

*** What size prop would be recommended for this motor, the existing one just removed edge to edge is appx 48mm with the Kort being 50mm. So I need to be using something smaller, but hopefully without changing the motor as well.



cheers
Andrew

Title: Re: Removing a brass prop problem
Post by: sailorboy61 on October 15, 2010, 07:27:32 PM
Should be ok with that size prop if aligned correctly... if is catching on one side on a turn then the alignment is out sideways I would suggest.... a smaller prop should certainly fix it but  a bit of a waste of a kort.... I'm guessing you don't want ot mess with the kort/shaft?
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 08:30:46 PM
Not so much a case of worrying one way or the other about the Kort - it wont come out  >:-o
Title: Re: Removing a brass prop problem
Post by: Shipmate60 on October 15, 2010, 08:57:05 PM
Andrew,
That isn't like you.
Accepting second best, go on rip it out and fit it properly, you know you want to!!

Bob
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 15, 2010, 10:08:57 PM
I would love to Bob, but the bl**dy thing is sealed into a very small area in the hull, and I cant even get my pliers in there.

Knowing the way things are recently I would probably try and pull it away from outside and pull the entire back end off the boat  :-X

Slightly smaller prop now on, will see what happens in the water on Sunday ............ then probably curse  :-))
Title: Re: Removing a brass prop problem
Post by: Shipmate60 on October 15, 2010, 10:20:45 PM
But you KNOW you won't be happy with it.

Bob
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 16, 2010, 08:22:34 AM
if it goes well, and the battery lasts a long time I will  O0

If the thing packs up in the middle of the lake  <*<    >>:-(         to say the least
Title: Re: Removing a brass prop problem
Post by: Dreadstar on October 16, 2010, 08:49:50 AM
I'll probably get shouted at for suggesting this,but could you not just file the tips of the prop a little to stop it fouling on the edges of the kort? That would seem to be the easiest solution to me.
Title: Re: Removing a brass prop problem
Post by: BlueWotsit on October 16, 2010, 09:58:26 AM
not really, dont forget brass props are finely balanced, it would be easy to disrupt that by filing the blades in my opinion - might be wrong I dont know