HELP - my prop shaft has come out

[Markinaboat]

14 hours ago, Strettonman said:

Does this help. The wood underneath is just there to catch the key as I was trying to shove it all back together. 

Not sure if it is helpful but the 2nd photo is the key I recovered. 

difficult to tell from the photo but assuming some of the white/ivory colour of the coupling has blackened with dirt, could it be one of these?

 

http://www.randdmarine.com/flexiblesc.asp

[Tony Brooks]

As Biz said those couplings were often shrunk on and in my experience once they start to move on the shaft become increasingly difficult to retain. This gets worse if there is any misalignment. I can't see how deep the dimple in the shaft is but if it is a dimple rather than a hole it may be worth deepening it a bit. It would also be worth checking the alignment and possibly starting to research the couplings that clamp on.

 

FWIW when on the fleet I gradually changed the fleet from that type to a taper, key and nut. Much more secure and easier to get the coupling off than a shrunk on one.

 

[bizzard]

Talking of shrunk on metals. Years ago on the GWR, I think it was on one of Daniel Gooch's egines, a single wheeler. The train was approaching west London on its way to Paddington when one of the shrunk on huge driving wheels flanged tyres came adrift, snapped and fell away. Luckily he engine was of rigid frame, no fore or aft bogies just a pair of carring wheels front and rear 2-2-2 arrangement. Those four carrying wheels kept the engine on the track and it limped into Paddington safely.

   Another example was when the Standard Britannia 4-6-2 Pacifics were first introduced the driving wheels were shrunk onto the axle ends. On a few occasions the wheels slipped on the axle ends throwing the wheels out of quarter, bending the coupling rods and lots of other damage. The reason was that to save weight the axle ends are hollowed out, ''normal practice'' but on the Britannia's they had bored them out two large and weakened them which caused the wheels to move on the axle ends, something that Churchward had found out about 70 years before.   Also years ago the car company Rootes Group had trouble with shrunk on flywheel ring gears shifting and slipping round on the flywheels, this was on certain late 1950's Hillman Minx's, Singer Gazelle's.

  Incidentally one of the Britannia's caused a serius accident on the S&C railway when the wheels shifted on the axle, broke a coupling rod which fell down and ripped up some of the adjacent track de-railing a train coming in the opposite direction.

 

I was wrong. It wan't shrunk on wheels that caused the S&C railway accident, it was an almost inaccessible bolt that had undone and fallen out which held the crosshead slide bars to the cylinder casing, causing the connecting rod to bust and fall down, digging up the track.

Edited February 24, 2019 by bizzard

[Strettonman]

Damn website - was sure I’d hit submit this morning 

———

Thanks all. Got it sorted this morning. Found the grub screw in the bulge water. Managed to push the prop on about 1/2 an inch using the pole as a lever and wiggling the prop at the same time. Started the engine and (very gingerly) put it into drive. The prop went all the way home straight away and the grub screw hole lined up perfectly. 

 

Fitted grub screw screw securely and tried reverse on tick over. No problems at all. 

 

AMAZING !!!!!!

 

will still follow the advice about avoiding reverse. 

 

Thanks so much to you all. Hopefully another happy day of boating. Just need the sun to shine now???. 

[Strettonman]

Good days gentle boating - off the the pub now. Think the prop shaft bearing might be on the way out which might explain extra vibration causing the grub screw to work loose. There are 3 grub screw holes in the coupling and the shaft has a hole right through as well as the dimple but so far I’ve stock with using the dimple. 

Can I just bolt right through the prop shaft and coupling or is the grub screw a designed weakness for any reason ? 

 

[Boater Sam]

If the holes in the coupling and the shaft line up in one position it probably was meant to have either a shear pin or a bolt and nut fitted through.

I cannot see just one grub screw and its dimple being a satisfactory method of securing the coupling to the shaft. Engineering-wise its not sound.

[Bee]

4 hours ago, Boater Sam said:

If the holes in the coupling and the shaft line up in one position it probably was meant to have either a shear pin or a bolt and nut fitted through.

I cannot see just one grub screw and its dimple being a satisfactory method of securing the coupling to the shaft. Engineering-wise its not sound.

You're right. Basically when reverse is engaged you have all the pull of the propeller trying to haul the shaft out of the coupling and all the momentum of the boat pulling the other way. The only thing that keeps it all together is a grub screw in a dimple. The best (and expensive ) way is to put a thrust bearing between the gearbox and the stern gland bolted to the boat. This will also stop wear to the stern gland as the engine wobbles around. However as there is some sort of flex coupling there and you won't be making offshore passages in stormy seas I would just enlarge the grub screw hole, drill about half an inch into the shaft and tap a thread into the lot and bung a bolt in, or drill right through the coupling, shaft and out the other side and bolt that up.

[RLWP]

5 hours ago, Boater Sam said:

If the holes in the coupling and the shaft line up in one position it probably was meant to have either a shear pin or a bolt and nut fitted through.

I cannot see just one grub screw and its dimple being a satisfactory method of securing the coupling to the shaft. Engineering-wise its not sound.

This is probably the missing solution:

14 hours ago, Strettonman said:

There are 3 grub screw holes in the coupling

 

Richard

[roland elsdon]

I had similar issue on my first boat, looks same set up plastic breaky coupling , keyway and grub screw.Being broke and young (dumb) and owning a honda genny and a black and decker i drilled a hole through everything and put in a bolt. I sold the boat a year or so later and never heard of any issue