Prop shaft coupling

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eddystone

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I want to loosen the prop shaft so that I can push it back and replace the Volvo seal
It's a split type coupling with 4 bolts but I thought there was also a screw; what I have got is a hole probably 2cms deep at right angles to the prop but there isn't anything in it - it has a slight conical depression at the bottom
Any ideas?
 
Is the hole threaded? Assuming 'yes', it sounds like the grub screw that was there has come out. Loosening the four bolts should allow the shaft to be moved, although this is not always straightforward. Some hints on the website.
 
The Yanmar coupling I took off my 35mm shaft when replacing the engine had four Allen headed bolts and a smaller allen headed machine screw grub bolt which went into a shaft indentation. It had an allen head and was locked with a nut.
It looks as though yours has gone walkabout.
Edit... posts passing in the ether!
If your grub=bolt has been ground off it looks like you will need to drill it out...carefully.
 
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Well having managed to release the shaft from the coupling I have discovered the hole is just decorative i.e. it doesn't go right through the coupling - the inside face is completely smooth. I'm guessing they come like that leaving the fitter the option to drill it through into the shaft and tap it for a retaining screw. The original fitter clearly didn't bother.
It may not be best practice but as the shaft has stayed on since that coupling was fitted in 2006 and the marine engineers who fitted a new shaft and stern seal in 2014 didn't change anything.
Again going back to Viv Cox's website it does refer to the Yanmar pattern coupling only relying on the bolts.
 
eddystone said:
Again going back to Viv Cox's website it does refer to the Yanmar pattern coupling only relying on the bolts.
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And is perfectly satisfactory on low HP engines. In fact, the big problem is usually getting it off! Of course if the 4 bolts are not done up and the shaft does not reach right to the end there is a possibility that it will slip and wear the shaft.
 
Tranona said:
And is perfectly satisfactory on low HP engines. In fact, the big problem is usually getting it off! Of course if the 4 bolts are not done up and the shaft does not reach right to the end there is a possibility that it will slip and wear the shaft.
Click to expand...

I made a couple of hardwood wedges to prise the two halves apart and shaft came out easily
 
Tranona said:
And is perfectly satisfactory on low HP engines. In fact, the big problem is usually getting it off! Of course if the 4 bolts are not done up and the shaft does not reach right to the end there is a possibility that it will slip and wear the shaft.
Click to expand...

There is also the possibility it will slip right out when you are reversing and only stop when it hits the rudder. This may or may not be after it has come right out of the shaft seal. I'm glad mine has the grub screw, actually it's more of a cone pointed 10mm bolt with a lock nut on it.
 
Spyro said:
There is also the possibility it will slip right out when you are reversing and only stop when it hits the rudder. This may or may not be after it has come right out of the shaft seal. I'm glad mine has the grub screw, actually it's more of a cone pointed 10mm bolt with a lock nut on it.
Click to expand...

There is always that possibility if it is not done up properly but there are thousands of these clamp couplings in use and when did you hear of that actually happening?
 
Spyro said:
There is also the possibility it will slip right out when you are reversing and only stop when it hits the rudder. This may or may not be after it has come right out of the shaft seal. I'm glad mine has the grub screw, actually it's more of a cone pointed 10mm bolt with a lock nut on it.
Click to expand...

Mine is the same. The charter company I bought the boat from had an identical boat, but without the grub screw in the coupling. It lost its shaft and propeller, as the shaft fell right out of the boat because the rudder is so far back from the P bracket on a Jeanneau 45.2 that it can fall out without reaching the rudder. The boat took on a lot of water before someone worked out where it was coming from and managed to get a bung into the Volvo seal.. The extra bit of safety is to put a shaft anode onto the shaft just ahead of the shaft seal so that if the shaft does come out of the coupling it can go nowhere, and no water gets in.
 
Tranona said:
There is always that possibility if it is not done up properly but there are thousands of these clamp couplings in use and when did you hear of that actually happening?
Click to expand...
I'm sure there are but there are also thousands that have a grub screw or some other form of locking device such as a nut on the end of the shaft inside the coupling. I'm sure they are there for a reason.
 
Spyro said:
I'm sure there are but there are also thousands that have a grub screw or some other form of locking device such as a nut on the end of the shaft inside the coupling. I'm sure they are there for a reason.
Click to expand...

Not totally relevant but the drives on very large equipment such as turbine driven compressors and generators, we are talking megawatts here, some up to 100 MW with shafts up to 12 inches diameter, rely totally on friction between the tapered shaft and coupling. Keyways are never used today as they generate fatigue cracks. Grubscrews would be pointless. Flanges are shrunk on to shafts, thermally with smaller ones, hydraulically with bigger. No other form of attachment.
 
Norman_E said:
The extra bit of safety is to put a shaft anode onto the shaft just ahead of the shaft seal so that if the shaft does come out of the coupling it can go nowhere, and no water gets in.
Click to expand...

I've got my "safety" shaft anode on the shaft just in front of the P bracket. I figure if it's outside the hull it can actually do some work as an anode, plus if your shaft seal is a rubber Volvo or similar then a spinning anode colliding with it inside the boat could do damage and start it leaking in the event of the shaft coming out of the coupling, whereas if the front of the cutlass bearing gets a bit damaged then that is less serious.
 
And it was going quite well until I tried to push the end of the shaft (after removing any rough bits and smoothing it) through the seal - it just pushes the orange lips protector off; tried getting someone else to push the shaft through whilst I held the seal on the end of the shaft - fail gain. Looking inside the seal I'm not surprised - the end of the lips protector forms a ridge the shaft won't slide over, especially as the two sides of the split ride over one another. Any ideas? I may of course have now damaged the lips and have to get a new seal. Part of the problem with the Sadler is there is such a short length of shaft between the hull entry and the coupling.
 
Try doing it in the water. No chance of drying out or lifting out last time that I had to do it. Previous seal damaged as a result of gearboxoutput sliding off. The drive plate of your gearbox may be held on with one bolt with no locking ddevice.....
 
Spyro said:
I'm sure there are but there are also thousands that have a grub screw or some other form of locking device such as a nut on the end of the shaft inside the coupling. I'm sure they are there for a reason.
Click to expand...

Yes, particularly those which rely on a split clamp where there is a perfectly good reason why a locking screw is not fitted. Other types do not rely on clamping but on other means of securing the coupling to the shaft, hence the additional physical fastening.

Rather pointless argument really. The loss of a shaft from a coupling is a very rare event and almost always due to improper assembly. So if you follow the instructions for either type they are just as secure.
 
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