Prop shaft too long?

[Jokani]

After a battle removing the existing existing coupling (the grinder eventually won).

Having tried two different couplings, neither of which fitted due to my retainer pin being too large. I contacted R&D marine who advised I would need to fit a flexi-coupling in between, which I have:

There is now a 63mm gap between the cutlass bearing and the prop:

Is this OK, or do I need to reduce the length of the shaft?

 

[JVL]

I would say that's over long iircc "approx not more than the shaft diameter beyond the bearing"

John

 

[GrahamHR]

I would say that's over long iircc "approx not more than the shaft diameter beyond the bearing"

John

That looks long; maybe the time for a big shaft anode and a large very aggressive rope cutter !

 

[Tranona]

Yes. Not sure why you had difficulty in finding a coupling to fit your shaft, nor why the retaining pin should be a problem as there are couplings that do not require retaining pins. if you do want a flexible coupling then suggest you look at a Centaflex or a Vetus Bullflex, either of which is shorter than the complicated arrangement you have and neither requires a retaining pin. The Centaflex is locked onto the shaft with a cone arrangement and the Bullflex is simply clamped on. You can also get solid couplings that are clamp on.

The gap between the cutless and the prop should be a minimum of 15mm, but up to 45mm is common if a rope cutter is fitted. Your 63mm is excessive.

 

[scottie]

How far does the shaft go into the coupling?

 

[Jokani]

Yes. Not sure why you had difficulty in finding a coupling to fit your shaft, nor why the retaining pin should be a problem as there are couplings that do not require retaining pins. if you do want a flexible coupling then suggest you look at a Centaflex or a Vetus Bullflex, either of which is shorter than the complicated arrangement you have and neither requires a retaining pin. The Centaflex is locked onto the shaft with a cone arrangement and the Bullflex is simply clamped on. You can also get solid couplings that are clamp on.

The current flexi-coupling supplied by R&D does not fit perfectly, as it does not fully site over the register, and keeps the whole clamp 2mm away, I have written to them asking if that is acceptable, but I guess not.

At the moment I would go for any coupling that would fit. Given that the old coupling had to be cut off, I don't think I can remove retaining pin?

The retaining pin has a diameter of 42mm and the register is 60mm

 

[Talulah]

That will not last long like that. Pretty sure the bolts will fail sooner rather than later.
Personally I would get a metal ring made up to fill the gap.

 

[earlybird]

Unusual IMO to see the gearbox flange threaded to take the connecting bolts. Nuts, preferably ny-locks, are more usual, but no room in your case. This, together with the lack of proper seating of the coupling faces, will make these bolts more likely to loosen in service. Locking with tab-washers under their heads would be an improvement, but the gap between the coupling faces is wrong, and should be eliminated.

 

[Tranona]

At the moment I would go for any coupling that would fit. Given that the old coupling had to be cut off, I don't think I can remove retaining pin?

The retaining pin has a diameter of 42mm and the register is 60mm

Do you have photo of the gearbox coupling and the end of the shaft without the coupling fitted? Can't get an image of a 42mm retaining pin in my head - i assumed it was a pin through the old coupling and shaft.

 

[Jokani]

R&D Marine have suggested that the bolts are too long and bottoming out, which would stop the coupling pulling tight. I'll check this out.

Once I have solved this, I will follow the above advice and have the prop shaft cut to the correct length.

 

[Jokani]

Do you have photo of the gearbox coupling and the end of the shaft without the coupling fitted? Can't get an image of a 42mm retaining pin in my head - i assumed it was a pin through the old coupling and shaft.

Here is the old coupling before it was removed:

Just to be clear the 42mm was the diameter of the retaining pin (if I have my terminology correct) the register diameter is 60mm

 

[earlybird]

From picture, is your problem the R&D failsafe strip hitting the spigot that projects beyond the register on the g/box coupling face?

 

[Tranona]

Is that a keyway in the shaft, and is there a taper on the end with a retaining nut? Do you have the PCD of the gear box coupling and its diameter?

 

[Jokani]

From picture, is your problem the R&D failsafe strip hitting the spigot that projects beyond the register on the g/box coupling face?

I think that 'spigot' is called the 'retaining pin'? But I'm not sure with the terminology here, keen to lear though as it can help in conversations with manufacturers etc.

I'm pretty sure it the failsafe stripclears this, but I will double check

 

[Jokani]

Is that a keyway in the shaft, and is there a taper on the end with a retaining nut? Do you have the PCD of the gear box coupling and its diameter?

Yes that is a key way, here is a pic taken just after the coupling was removed:

It is a 4" coupling and the gearbox 'flange'? is also 4", I believe the PCD is 80mm

 

[Tranona]

Think you will find that the coupling is the same as the Volvo MS type. Simplest way of dealing with the problem would be to fit a spacer about 15 or 20mm thick onto the gearbox coupling to bring the face flush. You could either get one machined, but you may find the spacers supplied by Ambassador Marine for installation of rope cutters will do the job. see www.ropestripper.com Give them a call to check. You could then do away with the flexible coupling, bolt the shaft coupling up and it would reduce the overhang to a more acceptable level.

 

[Lakesailor]

It looks to me as though the white spacer in the centre of the coupling is bottoming on the spigot in the centre of the output flange.

You won't pull the coupling in to mate with the flange with that there.
Easy answer is the coupling is unsuitable.

Whatever work-around you come up with to get things better is not right. A coupling that mates with the flange is what you need. If it is not as long overall, and allows the correct projection of the prop shaft, that is what you need to aim for.

 

[rogerthebodger]

I have a bullfles coupling and this type allows the prop shaft to protrude through the coupling at it does on my installation.

http://www.vetus-shop.com/vetus-bullflex-coupling-type1-shaft-25mm-p-971.html

Vetur may even have an adaptor plate to fit your gearbox.

 

[Jokani]

I have a bullfles coupling and this type allows the prop shaft to protrude through the coupling at it does on my installation.

http://www.vetus-shop.com/vetus-bullflex-coupling-type1-shaft-25mm-p-971.html

Vetur may even have an adaptor plate to fit your gearbox.

That does look a good coupling, but about 5% the worth of my boat ;-) But it is an option! I came across this product as well that could help if I cannot get the current flexi-coupling to fit:

http://www.vetus-shop.com/adapter-flange-for-volvo-ms-msb-and-all-types-ms2-p-1002.html

 

[pvb]

That does look a good coupling, but about 5% the worth of my boat ;-) But it is an option! I came across this product as well that could help if I cannot get the current flexi-coupling to fit:

http://www.vetus-shop.com/adapter-flange-for-volvo-ms-msb-and-all-types-ms2-p-1002.html

Surely the hole in that isn't big enough to accommodate the bit you've referred to as the "retaining pin".

A simple metal spacer, as Tranona suggested, would be the easiest solution. The Ambassador ones he mentioned are available in various thicknesses - http://www.ropestripper.com/accessories.php