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[Nige52]

On one of my boats which I bought secondhand, I'm having to replace the electric motor and Huco coupling as they weren't aligned correctly, the motor was horizontal and the prop shaft was at about a 20 degree angle downwards, meaning the Huco was working overtime and everything overheated when used. I have bought a new motor, a Graupner 700bb and I'm about to buy a new coupling as the motor shaft size is bigger, 5mm instead of 3.2.
Anyway, I thought I'd service the prop shaft whilst everything was apart, it's a standard brass tube with bronze bushes and takes a 5mm shaft. threaded both ends.

On inspection, I found the shaft pitted in places and end nuts seized, I got them off ok though. I cleaned everything up, re-cut the threads nice and clean and oiled the shaft before putting it back in the tube. Now I find that the shaft feels like it has grinding paste in when turned by hand if you know what I mean....It's fairly free in movement, but not clean and smooth.

Now, the very last thing I want to do is replace the whole tube, which would mean ripping the boat apart to get the old one out as it's been very firmly Araldited in...is it possible to buy just a new shaft from anywhere? Or is there something else I could try?

Many thanks
Nige

[BarryM]

Nige,

If it's just dirt overlooked then you may sort it by disassembly, flushing with white spirit, drying thoroughly and then re-packing with grease.

If that doesn't fix it then you might consider extracting the bearing bushes which are a press fit in the tube and replacing them and the shaft. Either make your own or get another shaft/tube unit and extract the bushes (carefully).

If all that fails then I'm afraid it's out with the grinder and saw and cut the whole tube out.

Whatever you do, make sure the new motor and shaft are properly aligned or you are just storing up trouble for yourself.

Good luck,

Barry M

 

[Nige52]

Thanks for that Barry,
I can't understand why the motor was installed the way it was...no matter, the Graupner 700bb should be a better motor anyway and it'll give me something to do I suppose....There is a new propshaft for sale on the auction site (PROPSHAFT 5mm BALLRACED stainless steel 200mm M5 8") which I might invest in if I have to.

Cheers
Nige

[Nige52]

Oh, and another related question:
Would that ball raced prop shaft assembly be better than one with an oiler on?

Thanks again
Nige

[BarryM]

Perhaps in theory - yes (Thinking of friction in bushes v. bearing races). In practice, I don't think it will make any difference.

However, if you are thinking of transferring bits from the new unit to fit in the old tube you may well have a compatability problem. I assume you are thinking of the worst case scenario and having to change the whole caboodle?

Barry M

[Nige52]

Yes I am unfortunately...my dremel is shivering with anticipation in the corner..............

[Shipmate60]

There is 1 possible far easier solution.
SHG produce replaceable propshaft bearings and if you bought a prop shaft of the right length this would fit.
The bearings are a hard wearing plastic material which I do not know how well they would run on a 700BB, but they are £1-00 and only take minutes to fit.

Bob

[Flying Sparks]

Nige

I have a simple idea that I used on my SHG Shadow. After I dug the boat out of the loft I realised that the prop shaft was a imperial size and finding new props could be an issue. I ordered a new 4mm Graupner tube and shaft assembly from cornwall model boats withe the intension of digging out the old tube and replacing with new. Then I had an idea, I pulled the bearings out of the old tube and the new assembly was a perfect fit inside. All I had to do then was smear on some epoxy to fix the new tube in place.

Phil.

[sheerline]

Nige, just one thing before you enact the dreaded surgery. You say you cleaned and oiled the shaft... but what with? If you used fine wet and dry or a pan scourer, you may have simply roughed the surface of the metal on the shaft so it will feel rough. Before you rip your boat apart, simply try polishing the shaft at the bearing points so that the bearings have a good smooth shiny faced shaft to work with.
Clean out the prop tube of old crud and degrease it, lightly oil everything and reassemble the whole shooting match once more. When you turn it over, it should feel a heck of a lot better and if you run it in for a while with your new motor you will probably find it all beds down quite nicely and will feel like silk. With another wash out and the application of a 'liittle' grease, it will probably go for years.
Worth a try and won't take much time to do.

[hollowhornbear]

if you heat the prop tube with a large soldering iron or other source of heat, once hot enough the epoxy will soften and you should be able to extract the tube with a little grunt but also with little damage to the surrounding areas, twist the tube as you pull, it helps to loosen the glue.
good luck.

[HS93 (RIP)]

A couple of things , 5mm SHG shafts are NOT 5mm they are the imperial equivalent, just under but two much under to use 5mm bearings, there compleat shafts  are good and cheap.

the one you where looking at on the web whose was it by the way there is one chap who sells fantastic shafts sealed for life and used by a lot of universeties for experimental ROVs they are about £20 but worth every penny and he will make whatever size you want.

as you have fitted a 700 BB take it you will be high reving if so don't use grease you are just giving power away, get one with an oiler and each time you sail just put a few drops in , the shg shafts are stainless and have bearings that use water to lubricate them, you don't actually need oil bit it stops the stainless getting deposits and lubricates the shaft when you run it on the bench as the bearings will melt if use out off water for prolonged periods.

To remove a shaft I have found that if you grip the outer end of the tube with Mole grips and turn, 9 times out of 10 they come out if not use heat  as well.

Peter

[More Coffee]

I could be possable that the oil is to light..May want to consider a heavier weight oil ..

[Nige52]

Thank you for the replies and advice 

I have got the shaft turning much better now, I put it in my cordless screwdriver, and using T-Cut on a rag, polished both ends and cleaned the tube out as best I could.

I found that when the 700 BB Turbo arrived, it was bigger than I thought and unsuitable for the job so today I put an order in to SHG for a fan assisted 550 plus an assortment of props, a new tube and shaft plus other odds and sods. I'll try the original tube to begin with and if I'm not happy, I'll have the new one waiting ready to drop in.....hopefully 

ATB
Nige

[BarryM]

Nige,

Never mind all that. Just put your Dremel on the end of the tube and whack it with the biggest hammer you can find. Gwan, gwan, gwan; you know you want to! 

Barry M