• UPDATED INFORMATION & ADVICE - PLEASE READ NOW

    'I didn't know/I wasn't told' will not be a valid defence if you fail to comply and lose your access to the off-topic area, core topic areas, or the entire YBW forum as a result. Full details can be found here, please read before you proceed.

Failed to remove the shaft coupling

Caraway

Well-known member
Joined
11 Aug 2019
Messages
6,067
Location
England
I'm not convinced we (Lucas or people on this forum) understand the joint.

What takes the fwd thrust?

Lucas says its not a taper.

So it must be parallel.

Interference fit? I've never seen one, how would the boat buikder have assembled it?

Grub screws? Do they penetrate into the shaft?

The key to getting the [Inappropriate quoted content removed] off is understanding the joint and how it was put together.

Or Lucas needs big boy pants and go banjax with the grinder. Shame to wreck the shaft.
Cut close to the shaft but parallel. Into the face of the flange. Then cut the remains of the flange face off on the outward facing part of the flange, away from the shaft. Gives you room to cut into the body of the flange and still leave a bit of it to avoid the shaft. Once you've piecemealed the fitting, a 2lb hammer and cold chisel will split the remains from the shaft.
Even if the shaft does get damaged, worst case, take it out, have cuts welded and machined back to original spec.

It's brutal, but there comes a time to get the job moving. :)
 
Last edited by a moderator:

Lucas Gan

Active member
Joined
5 Oct 2018
Messages
417
@stelican Because the starboard side stuffing box can't be repacked due to the nut being stuck and in a very tricky position not possible to access to use more force. The port side stuffing box can be repacked as its nut release ok. But they are all 29 years old already. That is why I doing this.
 

Alicatt

Well-known member
Joined
6 Nov 2017
Messages
1,598
Location
Eating in Eksel or Ice Cold in Alex
Cut close to the shaft but parallel. Into the face of the flange. Then cut the remains of the flange face off on the outward facing part of the flange, away from the shaft. Gives you room to cut into the body of the flange and still leave a bit of it to avoid the shaft. Once you've piecemealed the fitting, a 2lb hammer and cold chisel will split the remains from the shaft.
Even if the shaft does get damaged, worst case, take it out, have cuts welded and machined back to original spec.

It's brutal, but there comes a time to get the job moving. :)
and once he get's it off he finds that the flange was screwed on and the key way was to stop it rotating.

Well it's a thought.
 

TheCoach

Active member
Joined
10 Oct 2019
Messages
123
One more idea before the grinding starts. As you can access the keyway from the back have you tried sliding a suitable drift down that hole and seeing if you could tap/drive out the key. If it was on a taper this coming out would allow the flange to slide off?

Sorry if you have already tried this and I have missed it!

TC
 

Caraway

Well-known member
Joined
11 Aug 2019
Messages
6,067
Location
England
and once he get's it off he finds that the flange was screwed on and the key way was to stop it rotating.

Well it's a thought.
So far no evidence of that. He could try drilling the key out. But do you imagine a screw -on flange would line up the keyway in the shaft and the flange at the very point it became thread bound? Or do you think it would work with the thread tolerances still in play and just a key to prevent it moving?
If it were mine I would cut it off. Beause that will be the end result anyway.
 

TheCoach

Active member
Joined
10 Oct 2019
Messages
123
If you have to cut I would cut inline with the key way. Less metal to cut and no risk of damaging shaft if you get overexcited :p

If you damage the key itself that is probably just a bit of square stock anyway, and if you go for a split coupling won't be reused anyway.

If you do grind, on top of the good advice above get a old sheet or similar, soak in water and cover the surrounding area where sparks will land. Not only to minimise fire risk but hot sparks will embed into the grp and then rust making an awful mess(y)

TC
 

seastoke

Well-known member
Joined
16 Mar 2013
Messages
8,476
Location
boat conwy
keyway could have a small seloc pin holding it in the shaft so it will not slide . oh and have a fire extinguisher handy
 

longjohnsilver

Well-known member
Joined
30 May 2001
Messages
18,760
One more idea before the grinding starts. As you can access the keyway from the back have you tried sliding a suitable drift down that hole and seeing if you could tap/drive out the key. If it was on a taper this coming out would allow the flange to slide off?

Sorry if you have already tried this and I have missed it!

TC
Exactly what I was about to suggest.
 

TheCoach

Active member
Joined
10 Oct 2019
Messages
123
I'm not convinced we (Lucas or people on this forum) understand the joint.

What takes the fwd thrust?

Lucas says its not a taper.

So it must be parallel.

Interference fit? I've never seen one, how would the boat buikder have assembled it?

Grub screws? Do they penetrate into the shaft?

The key to getting the [Inappropriate quoted content removed] off is understanding the joint and how it was put together.
Fair point @burgundyben To my mind the "key" to this puzzle is the key! I've no real experience with marine applications hence why I was a bit quiet on this initially but in other engineering applications (automotive, machine rooms etc) a key is used to locate two rotating components and lock them together.

The grub screws would not have enough grip on circular shaft to deal with the torque applied unless they screw right into the shaft and would more likely be there to resist longitudinal movement of the collar on the shaft.

Could be talking utter nonsense of course, but my bet would be assembly process was flange on, grub screws nipped up, tapered key tapped in job done.

Unfortunately if the key is tapered then all the attempts at pulling the flange off may well have locked it even tighter in place.......😪

TC
 
Last edited by a moderator:

Lucas Gan

Active member
Joined
5 Oct 2018
Messages
417
The two screws just long enough to touch and press on the shaft surface, not penetrate the shaft.
 

seastoke

Well-known member
Joined
16 Mar 2013
Messages
8,476
Location
boat conwy
Fair point @burgundyben To my mind the "key" to this puzzle is the key! I've no real experience with marine applications hence why I was a bit quiet on this initially but in other engineering applications (automotive, machine rooms etc) a key is used to locate two rotating components and lock them together.

The grub screws would not have enough grip on circular shaft to deal with the torque applied unless they screw right into the shaft and would more likely be there to resist longitudinal movement of the collar on the shaft.

Could be talking utter nonsense of course, but my bet would be assembly process was flange on, grub screws nipped up, tapered key tapped in job done.

Unfortunately if the key is tapered then all the attempts at pulling the flange off may well have locked it even tighter in place.......😪

TC
if that was right if you knocked the flange forward it would be loose
 

Lucas Gan

Active member
Joined
5 Oct 2018
Messages
417
I now facing one more problem. I can't find the right size new coupling online! My coupling flange diameter is 120mm. The gearbox flange diameter is 121mm. So I think it should be 4 - 3/4 inches will fit. Not see a fit one online yet! Headache!
 

burgundyben

Well-known member
Joined
28 Nov 2002
Messages
6,576
Location
Niton Radio
Unfortunately, it's not coming off. Not even a little movement after 24 hours holding the steel plate with 6 bolts tighten to maximum and heated many times to untouchable hot. I am stuck!

I will just let it continues holding. I am trying to free up the stuffing box to keep using it. The problem is the stuffing box nut also won't move! Frustrating!
Are those bolts stainless?

If so, bin them, get some 12.9 bolts and nuts, get longer spanners, get them tighter, you need spanner 450mm long and a socket on a breaker bar same length.

Keep tightening. Round and round. Just keep going.
 
Last edited:

fisherman

Well-known member
Joined
2 Dec 2005
Messages
16,359
Location
Far S. Cornwall
The key is just a normal square key. Not looks like any hidden trick in there. I can see the keyseat hole from behind the coupling. Just can't remove the key anyway.
Yes, that pic banjaxed my longshot idea, just a normal parallel key. More force, better bolts. Thoroughly scrub the coupling with a wire brush, in case there's another roll pin or some such, neatly polished down flush.
 
Top