Prop shaft separated from gearbox

[Tupper32]

hi I have a volvo penta 2003 engine and yesterday whilst manoeuvring onto a mooring the prop shaft separated from the gearbox and migrated through the seal. I managed to push it back into the boat from out side and push back into the collar at the gear box and tightened it all back up and seems to be okay now.

Hairy moment as we were taking on water, we’re drifting in strong Easterly towards rocks and thinking the whole shaft and prop had been lost! what would cause this to have happened? picture of the prop shaft attached. thanks for any thoughts…

 

[vyv_cox]

I assume the hexagon-headed bolt should have a pointed end and engage with a deep dimple in the shaft. If not it would be worth arranging these.

 

[rotrax]

Island Packet fit the shaft, then mark and bore a 7/16th inch hole through both coupling and shaft.

An Imperial HT bolt and lock nut secures it even if the clamp loosens.

 

[rogerthebodger]

How is the collar with the hex bolt attached to the coupling that has the cap screws into the gearbox coupling

 

[Tupper32]

I assume the hexagon-headed bolt should have a pointed end and engage with a deep dimple in the shaft. If not it would be worth arranging these.

yes the bolt is now in the dimple on the shaft….we hit a crab pot last Summer and I wonder if it could have caused the shaft to come slightly dislodged as after I’d reseated it there is10mm very shinny metal close to the seal?

 

[Tupper32]

How is the collar with the hex bolt attached to the coupling that has the cap screws into the gearbox coupling

2 allen bolts

 

[Ianthediver]

hi I have a volvo penta 2003 engine and yesterday whilst manoeuvring onto a mooring the prop shaft separated from the gearbox and migrated through the seal. I managed to push it back into the boat from out side and push back into the collar at the gear box and tightened it all back up and seems to be okay now.

Hairy moment as we were taking on water, we’re drifting in strong Easterly towards rocks and thinking the whole shaft and prop had been lost! what would cause this to have happened? picture of the prop shaft attached. thanks for any thoughts…

can you tell me what size in diamita the shaft is on your boat?

 

[Boater Sam]

If the shaft has come out of a 2 piece clamp on flange coupler then there should be a grub screw in one half that should be in a dimple drilled into the shaft to prevent this.

 

[Ianthediver]

If the shaft has come out of a 2 piece clamp on flange coupler then there should be a grub screw in one half that should be in a dimple drilled into the shaft to prevent this.

I cannot find a grub screw my boat is 1999 did they have them then?

 

[sailoppopotamus]

Yanmar flange couplings don't typically have a grub screw. I fitted a new split half coupling from R&D engineering, which allows for a grub screw to be installed, but I intentionally (yet perhaps erroneously) did not install one.

 

[MontyMariner]

Dissimilar bolts can't be right.
The hex head looks to have a gap between the head and the clamp, so it can't be doing much clamping!

 

[Iliade]

Not uncommon for these to rely on the clamping force, but the shaft must match the coupling and the bolts must be torqued up to spec. eg the four bolt ones here are 54Nm.

If you were still feeling paranoid you could also fit a shaft collar so that the shaft couldn't escape altogether.

 

[Boater Sam]

I would drill it and fit a locking screw before it exits out of the hull altogether!

 

[Poignard]

If the hex-head screw is overtightened it will tend to open up the split-coupling, which is te last thing you want to happen.

 

[rogerthebodger]

If the hex-head screw is overtightened it will tend to open up the split-coupling, which is te last thing you want to happen.

If the hex head screw is overtightened on to the shaft that on its own will stop the shaft from loosening

I would like to know is that hx head screw dimpled into the shaft.

This looks like it is a alternative wy of what a grub screw would do

Grub screws are hardened an would tend to bite into the softer shaft even without a dimple

I have a deep row ball bearing thrust bearing on mt prop shaft which is held by grub screws and taper lock bushes on either side of the thrut bearing

 

[Poignard]

The torque is transmitted by friction between the inner faces of the split-clamp coupling and the shaft, not by the pointed end of the hex-head grubscrew.

As a matter of fact, my split coupling does not eevn have a grubscrew and it has not shifted in the 21 years it has been in service. It relies entirely on friction.

If a pointed grubscrew is to be used, this is a better arrangement:



Here the grubscrew is screwed in until it engages in the conical recess [dimple] and no further. Then it is locked in position with the locknut.

 

[rogerthebodger]

My prop-shaft coupling uses a taperlock bush to hold the prop-shaft in place but does use a key and keyway to transmit the torque

I have a flexable coupling between the prop shaft and the gearbox flange

I have a PSS seal which will also prevent my prop-shaft from exiting the boat

Together with the ball trust bearing I have belt braces and a piece of sting


The coupling you posted is machined from one piece of steel but the one the OP posted looks like 2 separate pieces and I cannot see how rge connection is made If it is one piee that is fine

 

[Poignard]

I only posted that picture to show the grubscrew as an example. The split-clamp coupling is not the same type as the OP's.

The OP's is one piece. I did find a photo of one like it this morning but I didn't keep it. I'll see if I can find it again.

 

[vyv_cox]

There are examples of just about every type on my website. Coupling types and removal

 

[rogerthebodger]

Yes the one you posted is from Norris which has 4 clamping screws 2 each side as the one I have on my workbench

The one the OP posted only has 2 clamping screws 1 each side which is why it also has the hex set screw to clamp on to the shaft

The R&D Marine 5" Split Clamp On Coupling also has 4 clamping screws

The higher max torque / prop shaft diameter the more clamping force is needed