Stubborn locking screw

oldbilbo said:
. . . . .The problem is the locking screw or stud....

This is about 8mm diameter, and there is a 6mm approx. hole down the approximate centre. That hole continues right through the body of the shaft-clamp and well down into the propshaft, but not all the way through. There is a corresponding but empty hole on the other side of the shaft-clamp body but no dimple or penetration on that side of the propshaft.The 'screw' top surface was recessed into its hole perhaps 1mm, and I suspect a previous owner had sheared off the top-slot intended for a screwdriver, then drilled down the centre in a failed attempt to remove it. A colleague considers that it is a roll pin, but there's no sign of concentric/spiral layers. . . . . .
Click to expand...

I have been following this thread and originally thought it was a 'Roll Pin'.

vyv_cox says it might be a grub-screw which is plausible BUT, the hole you have stated comes out the other side of the clamp which suggests a Roll Pin? If it is definitely a blind hole, no one would ever fit a Roll Pin in that circumstance, you would never be able to get it out!

Can you see, or test for, any thread form in this hole on the other side, you could use an opened out paper clip or dental scraper (if you have one). If it is threaded, it suggests Grub Screw but considering that it originally went right through, a Roll Pin.

roll%20pin.jpg

. . . . . . . . . . . . .Roll Pin


A Grub Screw would not require the hole to go right through so I am back to thinking about a Roll Pin. Your photograph certainly 'looks' like a Roll Pin? A Grub Screw would not require a 'dimple' (countersink)? :confused:

Dimples are often used as a 'guide' to allow you to locate a Roll pin during the initial stages of tapping home.

The only real way of removing a Roll Pin is to use a Parallel Pin Punch of exactly the OD or the hole or Roll Pin. It has to be a parallel pin punch. and a very light 1 Ounce hammer. Never use a heavy hammer otherwise you can shock damage the bearings of the prop-shaft or Cutlass Bearing.

Another point, as I do not think you are able to remove the complete shaft, if you apply heat, and I do not recommend it, you will require so much heat that you risk serious damage to oil seals on the output shaft of your gearbox. You would never be able to apply enough heat to anneal any Roll Pin or Grub Screw, under the circumstances in which you are working without doing damage elsewhere by heat conduction! :eek:
 
My Volvo 2003 has a similar arrangement although with 6 allen bolts holding the clamp together. The clamp and shaft are drilled through allowing a roll pin to be inserted. This is how it was supplied to me and has worked so far. The down side is that the hole is drilled off centre which means you can insert the shaft 180*ish out, you can insert the pin a few mm into the shaft where it can then jam, if hammered in I have no doubt it would go in further. Twisting the shaft through 180* lines the holes up perfectly. This might be what has happened here. Sadly I dont have an answer except using a captive hammer and large self tapper screwed into the pin which I have used on other occasions
 
When this thread reaches 50 posts, admit its not worth your time to pull the old coupling off in one piece- cut it off with a grinder and cutting disc, then cold chisel, buy a new one from R& D Marine and you will not have this problem the next time.
Another bonus, you will not have damaged the propshaft battering off the old coupling, and there will be a lot less blood in the bilges!
 
I have to admit to a modest degree of success today....


IMG_3260.jpg

​


….for which a lot of relief and some satisfaction is being enjoyed tonight. ;)

I started this morning re-measuring and confirming all the previously-recorded dimensions, for I suspected I’d need to order a set of cobalt drill bits. While measuring the depth of the clamp’s ‘rear’ hole, I noticed that it was not centred over the prop shaft as was the other one – it was 'out' by about 4-5mm – and on cleaning out the crud with an handy engineer’s scriber, I thought I could just make out ‘two shades of grey’ metal, one of which could possibly be part of the curved wall of a roll pin. Further, there was a pinprick of light coming through from the other side – inferring that the prop shaft was drilled right through.



IMG_3242.jpg



Cleaning up in there a bit more, I thought that I’d need to drill away the wall of the rear hole in the clamp so I could get a small drift-pin in there to try tapping the thing out. I anticipated that would not be easy, as several had suggested, but I thought to try a fine centre-punch that was to hand, just to see…...

Locating the point was done by feel, and a few light taps were tried – all I could manage in the tight space. Feeling round the back for any sign of movement, I was heartened to find the roll pin – for that is what it was – had raised its chewed-up head up by a couple of mm. Halleluia! A few more cautious taps and the pin head was proud by about 4mm – enough to grip! A few moments with a set of nippers, some twisting, and the darned thing was free. All 40mm of it……



IMG_3241.jpg



The way was now open to remove the flange-clamp entirely, which proved straightforward, then the two components of the damaged stern gland assembly and its old packing, which was the reason for tackling this in the first place. One can see the sheared-off bronze stud which has been drilled off-centre. That can now be taken to a workbench and ‘fettled’ properly.


IMG_3255.jpg


So, a RESULT!

And I’m hugely grateful to all of you here who made suggestions and helped bring my flawed understanding of what I was struggling with into a proper perspective. The forum at its best IMHO.

Next….? :D
 
Now, that is a result!
And with your clear pics and description becomes part of the forum archive for others to access in the future.
Cheers hic hic :)
 
Darn it ! I was looking forward to heroic tales of thermite lances, gearbox oil seals chilled by a flow of ice cubes stolen from the G&T bucket, and at the very least a performance by Avon Fire and Rescue Service with two ladder appliances and a pump unit.


I imagine that 'pleased ' is not the word - neat work, Cap'n.

So it's all downhill from now on ? :)
 
Well Done BB. ;)

One final and very important thing to do before you totally remove the clamp from the shaft.

With a Centre Punch (or a blob of paint or Permanent Felt tip Pen), punch or mark the casting with an indentation adjacent to that part of the shaft so that, just in case it is drilled slightly off-set, you will get the correct side to match up on reassembly. :)

Well done again. ;)


.
 
Well done and great photos.

With regards to various comments that roll pins should never be used in blind holes.. I have come across a great exception on the Volvo saildrive gearbox shift lever unit.

The small roll pin (of the type in your photos) is definitely inserted and the hole is blind. I spent ages looking at it just like we all have done with this. What was impossible to tell was that I had to hit the Volvo roll pin further in. It then passed into a very slightly larger diameter hole. This then enabled the parts to come apart and the roll pin just dropped out of the inner part afterwards.

What you hope is that the previous assembler doesn't leave the old pin in the blind part :(
 
Martin_J said:
Well done and great photos.

With regards to various comments that roll pins should never be used in blind holes.. I have come across a great exception on the Volvo saildrive gearbox shift lever unit.

The small roll pin (of the type in your photos) is definitely inserted and the hole is blind. I spent ages looking at it just like we all have done with this. What was impossible to tell was that I had to hit the Volvo roll pin further in. It then passed into a very slightly larger diameter hole. This then enabled the parts to come apart and the roll pin just dropped out of the inner part afterwards.

What you hope is that the previous assembler doesn't leave the old pin in the blind part :(
Click to expand...

Sneaky!
 
The two holes in my flange-clamp are, confusingly, not in line. Had they been, the makers' intention would have been clear, and I would have contentedly punched the pin out form one side or the other.

That was not the situation I found. The two holes were misaligned by about 20-25°, so that using a pin-punch would not have driven the roll pin out through the 'bottom' hole.

I have considerable respect for 'real injineers' with SX75-W90 and white grease under their fingernails, and I hold the belief that the 'misaligned' holes were made like that for a purpose. A purpose I am yet to discover......

VIP

To me, at least....

I do have the task of re-assembling the above transmission setup and choosing how best to 'pin' the flange-clamp to the prop shaft again, so that - should I ever need to repeat the exercise - I can do so without troubling over 2000 viewing forumeers making close on 60 post-responses.

There must be a better way...... :D
 
"There must be a better way"

IMHO taper lock bush. No cross drilled roll pin and IMHO easer to remove.

BTW drilling through a prop shaft as seems common significantly reduces the torsional strength of the shaft and can cause a failure point, That is why IMHO proper design Engineers use key ways or taper lock devices on drive shafts.

(Runs for cover)
 
Well done, and many thanks for the update. It's always great to hear how a problem has been resolved.

I wouldn't loose too much sleep over the hole. If your shaft hasn't sheared by now, it's unlikely to do in the future. Personally, I can't think of a reason why the holes were offset, but can only assume that it was a DIY job by a previous owner, done "by eye". If it were mine, I'd probably just leave the roll pin out on re-assembly. I very much doubt if it ever did anything, and trying to resist that combination of torsional and axial loading with a roll pin through "half" the assembly is a lousy way of doing it anyway. You could always put some marker pen lines on the shaft after re-assembly and check periodically that there's been no movement until you're reassured.
 
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