Working on a unit - Ships Nostalgia
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Working on a unit

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  #1  
Old 5th March 2014, 22:17
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endure endure is offline  
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Working on a unit

Can one of you engineery people tell me how you can work on one unit while the engine is still running? Can you disengage it from the crankshaft? If not how do you do it?
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  #2  
Old 5th March 2014, 23:05
paulm paulm is offline  
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Not possible !!.
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  #3  
Old 5th March 2014, 23:14
stoker stoker is offline
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Well....sometimes the bits "disengage" from the crankshaft by themselves, otherwise the answer is as paulm says....NO
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  #4  
Old 5th March 2014, 23:24
Fred Field Fred Field is offline  
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Beg to differ.
It depends on what the 'work' is. Should the con-rod still be connected to the crankshaft and the 'work' involve those moving parts, then I agree -NO!
However other 'work' is sometimes possible. There is even a video available of a tie bolt being renewed without stopping the engine on one of the very large Maersk container ships.

Last edited by Fred Field; 5th March 2014 at 23:46..
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  #5  
Old 5th March 2014, 23:57
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No you can not .
Stop the engine ; engage the turning gear ; make what turning is required to effect the repair . Then lock out the turning gear ( I used to remove the fuses and put them in my pocket ) so nobody can turn the engine with personal in the crankcase . Do your repairs and reactivate the system .
With a ship with two engines driving one shaft through a common gear box it is possible to shut down one engine for work . |However one has to physically block the clutch engagement of the engine being worked on and engaged the turning gear ; then proceed as above .
On a 2 Stoke on can hang up a fuel pump on a unit so there is no combustion in that unit ( allows a scavenge fire to burn itself out when running at reduced revs ) But you cannot work on the unit which is still turning .
On a 2 stroke it is also possible to stop the engine and "hang up a Piston at TDC " The piston rod has then to be disconnected . The connecting rod has then to be disconnected from the crankshaft and slung clear of the crankshaft throw and firmly secured . At that time some work could be done on a cylinder head etc. While the Engine is running on the remaining cylinders
Not to be recommended except in dire circumstances .
As a Unit consists of all the running elements ; a Unit by definition cannot be worked with the engine running .
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  #6  
Old 6th March 2014, 00:27
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Easy to do if you have a twin screw ship!

Bob
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  #7  
Old 6th March 2014, 00:39
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Cheers folks!
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  #8  
Old 6th March 2014, 00:49
Fred Field Fred Field is offline  
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Derek Roger.
I guess that we are going to have to agree to disagree. Either that or you did not read the second sentence of my post. I did qualify the situation.
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  #9  
Old 6th March 2014, 02:21
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Quote:
Originally Posted by Fred Field View Post
Beg to differ.
It depends on what the 'work' is. Should the con-rod still be connected to the crankshaft and the 'work' involve those moving parts, then I agree -NO!
However other 'work' is sometimes possible. There is even a video available of a tie bolt being renewed without stopping the engine on one of the very large Maersk container ships.
I saw that and they got it all wrong ( the commentators ) Initial comment was incorrect . They only worked on a tie bolt after slowing down no doubt ; not a big deal . They did NOT WORK ON A UNIT .
All engineers understand what a Unit is .
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  #10  
Old 6th March 2014, 09:24
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Quote:
Originally Posted by Fred Field View Post
Beg to differ.
It depends on what the 'work' is. Should the con-rod still be connected to the crankshaft and the 'work' involve those moving parts, then I agree -NO!
However other 'work' is sometimes possible. There is even a video available of a tie bolt being renewed without stopping the engine on one of the very large Maersk container ships.
It was a cylinder head stud that sheared (the narrator said it was a piston bolt?) No point in not to stop to tension a tie rod mainly on a Sulzer because of the main bearing tie bolts could come loose.(check out this forum https://www.shipsnostalgia.com/showth...ht=emma+mearsk )

Last edited by A.D.FROST; 6th March 2014 at 13:10..
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  #11  
Old 6th March 2014, 11:23
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I've seen work done on a cylinder while the engine was run on the test bed in Harland and Wolff. The complete "engine unit" was stopped, lower con rod removed and cylinder isolated before engine re-started. In all my years there I only seen this happen once so can only assume it was some sort of test or demonstration. NOT a procedure I would like to replicate when at sea.
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  #12  
Old 6th March 2014, 12:31
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A Denholm ship sail across the Atlantic with one unit hung up on a 3cyl.Doxford!
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  #13  
Old 6th March 2014, 12:35
Ron Dean Ron Dean is offline  
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Quote:
Originally Posted by Tmac1720 View Post
I've seen work done on a cylinder while the engine was run on the test bed in Harland and Wolff. The complete "engine unit" was stopped, lower con rod removed and cylinder isolated before engine re-started. In all my years there I only seen this happen once so can only assume it was some sort of test or demonstration. NOT a procedure I would like to replicate when at sea.
I can see this being done on an engine unit to allow some minor work to be carried out on the unit. With one cylinder isolated i.e. not functioning, the engine would be very much out of balance, though it could still run at a lower rated output.
I guess in general that the more cylinders an engine has, the better it will run with just one cylinder down. (Maybe a Vee 12 would run better than an In-line 7)?

Ron.
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  #14  
Old 6th March 2014, 12:42
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Run with a unit hung a couple of times (and with the fuel off a unit many times), in the manufacturers data there should be a table of barred speed ranges for various combinations of running gear removed, as Ron suggests dynamic balance is the problem. Also with 5 cylinder engines or less there is the potential problem of stopping in a "dead" position.
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  #15  
Old 6th March 2014, 17:08
Pampas Pampas is offline  
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One thing not mentioned, with a piston hung is the horrific noise this generates. When cotton wool was the only ear protector, really gets to you and the silence when finish with main engine is rung was a great relief,
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  #16  
Old 6th March 2014, 18:54
berbex berbex is offline
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As Fred above said, depends on the type of work, and the type of engine installation.

Resetting a Woodward governor after repairs on a Fairbanks Morse (generator in this case) required the engine to be running. Oscillations can be frightening (saw that first on a tanker generator in drydock, syncroscope even wilder).

On steam turbine gen governors it was a fairly frequent job. But it tested the nerves.

i have heard of other jobs done with engine running, but I believe sanity (or lack of it) had something to do with it.
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  #17  
Old 6th March 2014, 19:37
AlbieR AlbieR is offline  
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Just thinking, wouldn't it be an engineers dream to pull a unit when the engine was running, think of all the spare time in port to get "up the road" and join the R/O.

AlbieR
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  #18  
Old 6th March 2014, 20:58
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The best way to do a unit is in port on a "job and finish" basis.
Fast hard work them up the road to a good bar!

Bob'
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  #19  
Old 6th March 2014, 22:20
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I have a 1920s everyman slim volume on Navigation. The preface says that a high up navy admin man went on board a ship, his first comment was "Goodness, it's hollow!"

Reading this thread, this starts to seem like a sensible comment.

I had no idea that you did this kind of thing in the engine room, and other bits you had sway over. I admire you for the skills you had.
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  #20  
Old 8th March 2014, 12:51
Fred Field Fred Field is offline  
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spongebob - Great if you can do it, and I have, many times.

Ron Dean - The lower engine output with a unit 'out' slows the engine anyway and as Duncan112 states the manufacturer's information should be consulted for barred critical speeds. A further point is that there is a major difference in 'balance' with the con-rod disconnected and just the fuel shut off (fuel pump 'lifted'). SOP on the H&W double acting, opposed piston 2 strokes in the event of a scavenge fire.

Derek Roger - Well I guess I am not an engineer, because to me working 'on a unit' has a whole different meaning to 'doing a unit'.
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  #21  
Old 8th March 2014, 13:03
Fred Field Fred Field is offline  
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Derek Roger - I hope you do not mind but I believe you missed two very important points in your description of 'hanging up a unit'.

1. It can also be done with 4 strokes.
2. The lubricating oil flow to the bottom end has to be 'secured' (plugged). I have personally seen one instance of where this was done according to the manufacturer's instructions and with the builders supplied 'gear'. One problem I do not believe it had ever been tested running because the 'gear' disintegrated with damage to the engine. The manufacturer shall remain nameless!
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  #22  
Old 8th March 2014, 22:40
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Bottom line working on a unit ( as understood by engineers with the engine running )is a crock of sh1t . There are minor adjustments that can be made ; that is it that's all .
With the mass of a unit ( Con rod ; piston rod ; piston all doing 2 revs per second ; what are you able to do . I have given examples of how work can be carried out after a shut down to disconnect various components . That is all that can be done .
I find this proposal to be the worst of all engineering posts .

Real engineers please comment . Derek
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  #23  
Old 8th March 2014, 22:48
AlbieR AlbieR is offline  
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Quote:
Originally Posted by Derek Roger View Post
Bottom line working on a unit ( as understood by engineers with the engine running )is a crock of sh1t . There are minor adjustments that can be made ; that is it that's all .
With the mass of a unit ( Con rod ; piston rod ; piston all doing 2 revs per second ; what are you able to do . I have given examples of how work can be carried out after a shut down to disconnect various components . That is all that can be done .
I find this proposal to be the worst of all engineering posts .

Real engineers please comment . Derek
I refer to my previous post #17

AlbieR
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  #24  
Old 9th March 2014, 14:52
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Varley Varley is online now   SN Supporter
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#14 and #15.

Never ran with unit actually hung up but once with fuel off. Burmpac Bahamas.

Telex below says most but not all.

The crack was not one detected by nuances of water in oil or pressure fluctuations across the engine but with an obvious split emitting a sheet of flame a metre or so in length across the tops with every revolution, each accompanied by a loud ripping sound.

On the following morning as I gazed at this triumph of Italian engineering - more in amazement than awe, a Dante-esque tableau with blue smoke gently ascending from many open and leaking parts of the exhaust system and blowby (the underpiston space was open to the engine room) - there was a loudish bang followed by a hiss. It would have sounded like a large compressor unloading were it not for the hiss continuing.

The cooling water had been isolated as well as the fuel and overnight had been enough to boil the remaining water (or perhaps to raise the rate) sufficient for it to blow out a gasket in the jacket water connection.

Only a day or so onboard but unforgetable.
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  #25  
Old 9th March 2014, 16:29
Plane Sailing Plane Sailing is offline  
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Only a day or so onboard but unforgetable.

You escaped lightly, David. I did just over three months as C/O on her - left when she was handed over to new Greek owners. I still have nightmares about that ship, as I'm sure did most of the Engineers.

Not one of Denholm's finest vessels....................................
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