# Need help YANMAR engine mount



## Giulietta (Nov 14, 2006)

Hi,

Brand new Yanmar 3JHE 40HP, SD50 Saildrive, 150 hours only.

The front Port engine mount stud broke, clean between locking nut and engine support, (as if it was cut). 

Called Yanmar (complete engine installation by Yanmar also on brand new boat) and they immediately replaced the rubber mount, the stud and the engine support, rechecked all bolts and left. (gave me a free oil change, and filters).

They say never happened before, and the cause was material fatigue !!??

So far new parts are ok. Has anyone experienced this on a Yanmar??

I made a simple drawing of where it broke

Please help.


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## cardiacpaul (Jun 20, 2006)

It was probably a weak stud that was over-torqued at installation, I wouldn't worry about it any longer.


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## sailingdog (Mar 19, 2006)

i agree...sounds like it was overtightened.


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## TSOJOURNER (Dec 16, 1999)

Giulietta, 

I just saw this posting and would like to offer some additional input. If you still have the pieces of the stud, examination of the fractured ends will tell the story (magnification will help).

If the surfaces are rough, then the stud sheared off. More than likely, what you will see is a smooth area and a rough area. The smooth area defines a crack, and the rough area denotes the ultimate failure of the fastener. There are two sources of the cracking. The first would be a flaw in the base metal, such as a carbon inclusion (very common to this type of failure). The second would be the formation of a stress riser in the threaded area.

When threads are formed, they are rolled, a forging process. This process reduces the likelihood of stress riser formation, but it could occur. Another source of stress riser formation in threads would result from the use of a sharp die. If the threads had been damaged during the installation of the engine (very possible) and then a die run over them, the subsequent failure would be possible. If you have the pieces, you should be able to see where a die would have cut sharply into the root of the thread. 

I really don't like the design of this mounting. All of the engine weight and vibration are concentrated on the threaded portion of the stud. A better way would be to place spacers (they would have to be machined after taking careful measurements to maintain engine alignment) under the engine block tabs and on top of the rubber mounts (here I am assuming that there is a metal surface on the top of the rubber mounts). Above the engine block tabs, use a heavy flat washer and either a locknut (upset thread, not Nylon) or double nuts in a jam configuration (simply, one on top of the other with their flats misaligned). Use a thread locking compund, such as Loctite red.

You probably will never have any problem with what is in the boat now. The size of the studs are way over-spec'd to withstand the abuse of any compromise. However, if you continue to have problems, you also have the remedy. 

Regards, 
Bob

ps: Please take a look at my post in this forum regarding jib rigging. I need your input. Many thanks.


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## Giulietta (Nov 14, 2006)

Bob, Thanks for your help. I realy appreciate it.

The problem is the Engine is new, Yanmar installed it in June, so it is still under the warranty for some more years. And one of my crew is the guy that installed it!! He is the Piano Man, because he is so big!!!

They took the stud with them, and I could almost swear thet they new what happened and didn't want to talk about it, too much. 
I alm also inclined towards CP's comment " weak stud that was over-torqued at installation".

I had many options for engines when I had the boat built, and Yanmar was the winner (not cost related). I am sure that they will support their product.

I posted to see if it had happened to anyone else out there.

If I change the studs as you very well suggest, I will void the guarantee. So this is a case of sit back and watch.
The bolt was all smooth at the broken face.

PS Have you been to member galleries? I am posting some photos we did when the running rig was being installed, and of the testing. she still had the EXP logo on the side.


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## TSOJOURNER (Dec 16, 1999)

Giulietta,

Really wasn't suggesting changing the studs, just the mounting configuration. I'm sure there's no need to do anything at this time, especially with the warranty situation. If your guy did the installation, then you would know of any use of a die. 

If the Piano Man torqued the nuts, I suppose it's possible that he fractured the stud. My other thought is that as tough as studs are, the threads on the nut would have given up before the stud did.

Bob


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## Giulietta (Nov 14, 2006)

Bob, are saying he overtorqued the studs because he is the piano man?? ie very strong piano hauler?


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## TSOJOURNER (Dec 16, 1999)

Giulietta,

Yes, "very strong piano hauler". Actually, I don't think he is the cause of the failure. Getting a wrench on the lower nut and being able to resist the amount of torque imparted to the top nut that would fracture that stud just doesn't compute for me. I see the stud as being the strongest part of the whole system, unless it had a problem. I think the stud had a failure; I just don't describe it exactly the same way that Yanmar did.

I have had further thoughts regarding the mount configuration. The rubber mounts probably serve as vibration isolators; my solution would work just fine, except that it could transmit vibration into the mount pads in the boat. In any respect, there should be no reason for you to ever have to do anything further. I just don't like the idea of using threaded areas for structural purposes. They're great for imparting tension into the fastener. Beyond that, they're a liability. 

Regards,
Bob


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## Giulietta (Nov 14, 2006)

Bob, I am going to get a camera and send you a detailed photo, of the arrangment.

Might take a week or two, but will do.

The Piano Man, normally (over here) is the guy that has his body inside the cabin, standin on the first step in the cabin, and stays next to the clutches, and handles the clutches, boomjack and cunningham!!

Piano Man, because the clutches looke like the keys of a piano!!!

I edited later. here are 2 shots of the same engine, however the 1st one is not the saildrive one, but same engine it has 4 mounts. I posted it because you can zoom in on the mount easier.

The saildrive one 2nd photo, only has 2 monts on the front. The rear end is supported by the saildrive (no mounts)


If you copy and paste the photo yoiu can see the mount


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## TSOJOURNER (Dec 16, 1999)

Giulietta,

Now I understand why you said the studs would have to be replaced; they are threaded all of the way to the base. As I see it, my method would simply place the loading stress over a longer portion of the threads, increasing the opportunity for the stress to find a riser. 

BTW, I didn't know that you are an engineer when I imparted my solution. Anyway, we understand each other. I don't think you need to go to the trouble of taking additional photos, at least not for my benefit. That's a really good look at the saildrive. 

Regards,
Bob


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## quiksilver (Sep 18, 2007)

*Broken Yanmar engine mount*

Hi,

I had the exact same problem with broken engine mounts on Lagoon 410 S2 catamaran with approx. 500 engine hours, factory installation. It has two Yanmar 3jh4e engines with sd50 saildrives and two mounts on both engines + one mount on saildrive, so the engines are supported on 3 points only. So the two mounts of both engines broke at exact same place on the studs, leading to a broken and severely leaking saildrive double seal on SB engine due to twisting. The Yanmar service at Gran Canaria is a joke so in the end I had to have the studs welded back together and stuff a part of water hose to the saildrive seal to make the leak smaller and sail back to Estonia like that.

I also remember reading about someone else having the same mounts breaking.

Karmo


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## Giulietta (Nov 14, 2006)

My engine mount (only one broke) broke in November 2006, after 150 hours in service. And we had sailed in pretty high seas and winds with the engine on for 20 minutes, which I believe its when it broke..luckily never had problems with the saildrive leak...

Anyway, the new mount was installed right then, and since then my engine only worked 50 more hours, most of them sailng the boat to where it is now in July.

So far so good, and I do check them periodically...

Thanks for sharing and explaining your case..I will transmit it to my Yanmar friends.

Why didn't you stop in Portugal to repair?? Yanmar here is very good.


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## camaraderie (May 22, 2002)

I don't think the sail drive was meant for going 15 knots...the force of the water torqued the whole engine and broke your mount! (g)


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## Rockter (Sep 11, 2006)

I would buy a spare mount, or two, and watch the others.

Interesting that they took the old one away with them.


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## Giulietta (Nov 14, 2006)

They took it to send it to the manufacturer in Japan, to complete the complaint/guarantee thing.

I didn't want it any way.

Everything seems normal now, and I'm happy


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## jackytdunaway (Sep 11, 2006)

Broken boom, broken engine mount stud, who knows what else. Trade it in for a Catalina. CD can help you find one.


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## Giulietta (Nov 14, 2006)

ahhhh that was funny...but what would I do with a Catalina??? 

Be just one more guy with a Catalina???   

I like being different...and believe me, many more things will break starting in November..that's a guarantee   

By the way...can a Catalina do it???


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## theartfuldodger (Sep 4, 2006)

such a break is a defective bolt, for the real break if not installed right would have been at the mount, this happens alot in the automotive industry, and after test performed by labs, the bolt was not harden right. If you wish to know my experience 35 years in the automotive industry, heavy equioment and marine as well. I myself installed new engine in my 33 O/I Morgan two years ago, and works very good, thanks to Yanmars retrofit kit.

S/V The Artful Dodger


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## Giulietta (Nov 14, 2006)

theartfuldodger said:


> such a break is a defective bolt, for the real break if not installed right would have been at the mount, this happens alot in the automotive industry, and after test performed by labs, the bolt was not harden right. If you wish to know my experience 35 years in the automotive industry, heavy equioment and marine as well. I myself installed new engine in my 33 O/I Morgan two years ago, and works very good, thanks to Yanmars retrofit kit.
> 
> S/V The Artful Dodger


Thanks for your input..that was my initial idea, but they said otherwise..

anyway...all is fine now...


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## Kerkyra (Jul 27, 2009)

I just returned from a vacation on our Hanse 400, which also has a 3JH4E with SD50 saildrive. Our first day out we noticed the engine sounded different and I went below to find the engine was hopping around and both mounts had failed. I limped into port and was lucky to find a mechanic to weld on some replacement studs to hold the engine until I got some replacements a few days later. 

The failure was very similar to what was described by Giulietta in the original post, except both studs had failed immediately below the nut that supports the engine (not between the nut and the engine tab). I've tried unsuccessfully to upload some photos (800x600, <50kB). Our engine was also delivered in 2006 and has 900 hours on it.

I showed the photos to a mechanical engineer who had the same comments that "Bob" had earlier in this thread. He too was surprised that the stud itself was used to support the vibrating load instead of some kind of spacer. He explained that threaded rods are subject to failure fatigue if they are subjected to flexing as these ones would be. The threads weaken the rod because the strain isn't evenly distributed across the rod but is greater on the "inside" surface of the thread and less on the "outside" surface. (similar to the effect of a small nick in a wire that will cause it to fail by focussing the strain in one spot).

This explanation made very good sense to me and it was very interesting to read the corroborating explanation and same suggested solution from Bob. The diagram in the original post doesn't quite make as much sense to me because the rod wouldn't flex so much at the interface of the nut and the engine tab (could it be that the drawing is not quite right?) 

If the engine was bolted directly to the mount or if a spacer was placed between the engine and mount then the threaded stud would only function as a fastener and not a standoff and would not be subject to this failure mode.

I'll be sending some photos to Yanmar. One would hope that they have seen enough of this failure to realize there is a flaw to be addressed - perhaps with a field upgrade to add a standoff between the mount and the engine tab. I improvised one with my replacement mounts because otherwise I have no reason to trust that this won't happen again. I found some oversized stainless nuts which I placed between the top of the mount and the lowest nut (the nut that holds the stud on the mount), with a washer in-between. This provides the same spacing as the original installation but essentially creates a "stack" between the engine and the mount, with the stud used only to hold it together. (again, I have a photo but can't upload it).

I was very happy to see Bob making the same suggestion so hopefully I've made an improvement. I think he is bang on with his comment about using threaded fasteners for structural members.

Thanks very much to SailNet, and to Giulietta, Bob and Quiksilver and others for sharing their information and insights.


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## Kerkyra (Jul 27, 2009)

*Update on Yanmar mounts*

FYI: Just thought I'd update this to say that my modified mounts are still OK, and that I never received a reply from Yanmar when I sent them a description and photos about this problem.

I strongly beleive that this is a design flaw that should have been fixed long ago - has anybody else had this problem?


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