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Failed Engine Mounts

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landlocked View Drop Down
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    Posted: 28 July 2009 at 07:20
On the first day of our summer holiday this year my wife remarked that the engine was making some different noises.  I went below and found it was making some different movements as well - jumping around a bit.   It turns out both of the forward engine mounts had failed, so the engine was only supported by the aft engine mount and the sail drive gasket. 
 
Fortunately it had been a good day for sailing and we were almost in port when I found the problem.  Also fortunately there was a marine mechanic on shore and working on Saturday who welded new studs on my engine mounts so I could carry on until I got the right parts a few days later.
 
Here's what I learned:
 
1.  The mounts appeared to be installed as specified by Yanmar and the bed for the engine is supplied by Yanmar and glassed in place at the Hanse factory.
2.  This has happened on other (non Hanse) boats with the 3JH4E engine and SD50 saildrive  http://www.sailnet.com/forums/gear-maintenance/25659-need-help-yanmar-engine-mount.html
3.  The mounts are different (stiffer) if you have a saildrive rather than marine drive (and not all dealers realize this!!).  9 bus rides, 1 ferry, 1 taxi and 1 "lift" from a friend and I finally had the right parts ("200" rating).
4.  The failure was a fatigue fracture of the threaded stud on top of the mount, and not too surprising given the vulnerability of this design (more on this below)
5.  Access through the side panels of the engine compartment is great.  Thank God.
6.  If you remove the companionway steps the main halyard can come straight down to the lifting ring on top of the engine.  Thank God again.
7.  Removing the companionway steps could be much easier if you didn't have to access the nuts on the back of the bolts that hold the hinges (maybe epoxy them in place for next time?)
 
Here's some more about the failure mechanism:
 
The bolts failed immediately below the nut that supports the engine tabs (I have a photo but can't seem to upload right now).
 
According to my mechanical engineering friends, threaded rods should only be used as fasteners and not structural members as they are in this case.  They can fatigue very easily if subjected to flexing forces.  This is because when you bend a threaded rod the strain is not evenly distributed across its length but rather concentrated in the valleys of the threads.  It's much like the effect of a nick in a wire - the rest of the wire is stiffer so when you bend it, most of the deformation happens in the nicked part and it quickly fatigues.  In the case of the threaded rod you really have a series of nicks that take up the strain of the flexing, instead of having it distributed evenly across the rod.  I was shocked at first to see these thick bolts had broken, but now that I think of them as vibrating rods with cracks encircling them it isn't at all surprising.  In my photos that you can't see just yet, it is clear that the fractures happened along the inside of the first thread below the nut that supports the engine (the first nick in the wire so to speak).
 
I expect that the higher you place the engine on the stud the quicker it will fail, and it may be that the 3JH4E/SD50 arrangement is a bit worse than most, and maybe mine were a millimeter or two higher than most.
 
The solutions that were suggested independently from two different sources were to put some kind of spacer between the top of the engine mount and the engine tab which will bear the strains from the vibration while the threaded rod is used only to clamp the engine down onto the spacer.  I have improvised such a solution for now (photo to follow), but will also take this up with Yanmar.
 
My advice is to beware.  Maybe even carry an extra pair of 200-rated Yanmar flex mounts (about US$208 each).  You may have a ticking time bomb in your engine compartment.
 
"Kerkyra" 400e #042
www.sailkerkyra.com
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2009 at 07:30
 
Engine mount and lower part of stud in foreground, engine tab and upper part of stud in background (the engine shifted to starboard and dropped down to rest on the top of the engine mount)


Edited by landlocked - 29 July 2009 at 04:20
"Kerkyra" 400e #042
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 04:09
 
Closeup of failed surface.


Edited by landlocked - 29 July 2009 at 04:19
"Kerkyra" 400e #042
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 04:19
 
After removing broken engine mount
"Kerkyra" 400e #042
www.sailkerkyra.com
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 04:40
 
This is the new replacement mount
"Kerkyra" 400e #042
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 05:08
 
Modified assembly. 
 
The stud is a sort of carriage bolt that passes through the top part of the mount and is normally fastened in place with a nut and lock washer (painted black).  In the photo above I have removed the nut and lock washer, placed an oversized nut and flat washer around the stud as a spacer, and then replaced the (black) nut and lock washer and tightened it down on the spacers.  I then sat the engine on the black nut and tightened the final nut and lock washer on top of the engine tab.  I think this should reduce the flexing of the stud.
 
If anybody thinks this is a bad idea, please let me know your thoughts. 
"Kerkyra" 400e #042
www.sailkerkyra.com
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panos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote panos Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 18:51
Hi,
Good job.
But I suspect that you cured the symptom and the cause is still there. I think that the cause of failure was intense vibrations caused by either engine malfunction or load misalignment.
I dont think that these huge bolts would fail under normal conditions (even though the surface mark theory is correct, but only marginally reducing the shear strength of the bolt)
Panos

Hanse 630e - selling her -
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landlocked View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote landlocked Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2009 at 19:54

I guess you're right that there must be a reason for mine to fail when others haven't (though apparently some others have), but I suspect that all of these installations are subject to the same failure.  It could be that the design is marginal so that depending on normal variations in manufacturing and installation some are more prone than others.

It could also be that something caused an increase in vibrations as you pointed out, and this brought on the failure.  I have a 3-blade prop which should cause less vibration than a 2-blade but it is also a folding prop and I suppose if it didn't fully unfold or if a stray piece of rope or something caught on the prop the vibrations could increase.   Still, it seems to me that there should be enough margin in the design of the engine mounts to handle this.  
 
My concern is that there is a "weak link" in the engine mount design which is the length of threaded rod coupling the engine to the mount, and I suspect that this is the component that limits the overall reliability of the mounting system.
"Kerkyra" 400e #042
www.sailkerkyra.com
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Captain Cook View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Captain Cook Quote  Post ReplyReply Direct Link To This Post Posted: 17 June 2017 at 21:13

I would like to add some information to this old topic from 2009.
My engine mounts broke in rough weather at sea between Sealand and Germany in the summer of 2012. I made a temporary repair at sea, and on arrival in Kiel, I ordered new mounts at the local engine-mount pusher (680euro) and replaced them. Later in 2012 I also replaced the rubber-diaphragm that support the SD50 saildrive. While sailing with broken mounts, the diaphragm had carried more load than designed for (and you should change it anyway after 7+ years???).
During the repair I were in contact with the danish Yanmar-agent, and he told that it was an error to place the engine on the mount with the upper nut at top of the thread. There should be 8-10 mm visible thread over the top of the upper nut. As can be seen on the picures from Landlocked, and on my pictures, Hanse werft has placed the engine with less than 1 mm of thread visible on his and mine boat. You will also notice a steel-wire with wire-clamps on securing the mount against severe movement. This is for use in rough seas. As can be seen, as Landlocked did, I reinforced the assembly a bit by stacking the nuts and strenghtening it with blue loctite. Until now - it works. Take a look at my upper nut and compare it with yours - as you can see I took faith in the advice I recieved from Yanmar - and placed the nut lower.










Edited by Captain Cook - 20 June 2017 at 17:07
Freya Hanse400#27
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Captain Cook Quote  Post ReplyReply Direct Link To This Post Posted: 18 June 2017 at 10:53

A few pictures more:









Edited by Captain Cook - 18 June 2017 at 11:27
Freya Hanse400#27
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