Broken engine mount stud

Sep 24, 2018
1,482
O'Day 25 Chicago
A temporary repair is easy. Remove the stud thats attached to to the engine. If needed, grind the mount stud down to some clean threads. From here you can use the two nuts from the broken part of the stud to attach a bolt on the engine side (buying new ones would be easier). Now use a "rod" coupler to connect the bolt to the mount. This obviously doesnt account for the offset. Two options come to mind...

The first might be to use a camber kit for a car. I can't remember if its just a cam with an offset or if the two halves of the bolt are offset. You will probably have issues finding a thread that matches your mount so some rethreading may be in order

The second is to use a piece of metal with two holes in it. Engine side gets bolted to one hole and the mount gets bolted to the other


A quick search revealed a few other more suitable options...


Offset trolley bolt


I just took a closer look at your picture and noticed adjustment slots on the mount. Can you just loosen those bolts and move the mount over?
 
Sep 24, 2018
1,482
O'Day 25 Chicago
If you can't move the mount laterally, you could shim it at an angle. Not ideal but it could get you out of a jam
 
Aug 22, 2017
1,608
Hunter 26.5 West Palm Beach
To keep the answer at a high level here is a summary type answer to your question.

Grade 8 bolts have a UTS of 150ksi, grade 5 120ksi ( assuming 1" or less bolt diameter). The plain carbon alloy required for both of these has a carbon content of 0.28 to 0.55% placing these bolts into a medium carbon type steel. If these are high strength stainless steel bolts they are likely a 400 series martensitic alloy. Whie the composition is different, the following discussion still applies.

First you would need an alloy appropriate filler rod. That's a big subject.

Then you have the problem of the HAZ - heat affected zone. The HAZ will contain a region of untempered martensite that is hard and quite brittle. Unless you heat treat this, you will find your welded bolt will snap off quite easily right next to your well.

In order to make a high strength bolt even close to it's original design requirements would require a full heat treatment for the entire bolt. Simply not a practical option in this case.

dj

Thank you for the eloquent & well supported answer to my question. Your concerns are all valid. They are also issues that I was previously familiar with. If I were to only rely on my “book learning” & I did not also have a fair base of real world experience welding motor mounts & suspension components, I would have agreed with your opinion & considered it to be gospel.

In the case under discussion, I suspect that welding the broken parts in their current (out of line) positions will result in more evenly distributed stress loads across the entire set of fasteners. I have found from experience that tapering the fillet allows pretty close to full structural strength when using soft (60ksi) rods on higher class bolts. I once welded a grade 8 bolt to a socket extension, to make a temporary tool to get me out of a bind. The tool ended up being far stronger than I had expected possible. As you suggested, I expected the edge of the weld to snap off like the bolt ears on a 30-40 Krag. I would later use cheater bars that were more than 20 diameters long to put heavy stress on my temporary tool. I was never able to break that tool after more than 15 years of trying. I never expected that.

I agree that filler rod selection is a fairly deep subject if you want to cover all the bases. I will just stick with a Cliff’s Notes type response here. 6011ish rods can get you what you need, in or out of position, in most cases when welding bolts if you taper your filets & watch you cherry (majority of the heat affected area). Even on stainless bolts, you can get good structural strength out of mild steel rods, but of course you don’t get any of the corrosion resistance, so that would be a weld of limited lifespan. When welding stainless bolts of unknown alloy, I have had good luck running 308 hi sil wire, when I wanted to keep the corrosion resistance intact.

I also agree that welding with the correct alloy filler rod, followed by full heat treat (you might want to use a little x-ray inspection in between) would be needed to gain 100% full certified performance from a repaired fastener like this, but I have field tested a lot of welded bolts that lasted me for a lot of years, back in the dark days when buying new parts was not in my budget.

Of course, replacing all motor mounts & properly aligning them is the best option. There is no doubt in my mind about that. Having the right guy hit the broken parts with a 6011 stick is a move that would likely buy you a season or two with just a few minutes of time invested to make it happen. It’s not a Bristol move, by any stretch of the imagination. Having the wrong guy hit that with a stick would likely result in a quickly broken weld, as you would seem to expect.
 

dLj

.
Mar 23, 2017
1,833
Belliure 41 Now on the Chesapeake
If I were to only rely on my “book learning” & I did not also have a fair base of real world experience welding motor mounts & suspension components, I would have agreed with your opinion & considered it to be gospel.
I always find it interesting that the assumptions are that I speak from strictly a "book learning" view point. I first became a certified welder in 1974. Then worked as a blacksmith making my way to eventually making pattern welded swords (e g. Samurai swords). That was all before I went on to my current career.

Can you make a weld that could work for awhile? A good welder can, sounds like you are one of those. But is that how I would want to fix my motor mount? Nope. I'd replace them. But at this point it's an academic discussion as the OP is replacing these mounts.

Respectfully,

dj
 
  • Like
Likes: JimInPB
Aug 22, 2017
1,608
Hunter 26.5 West Palm Beach
I always find it interesting that the assumptions are that I speak from strictly a "book learning" view point. I first became a certified welder in 1974. Then worked as a blacksmith making my way to eventually making pattern welded swords (e g. Samurai swords). That was all before I went on to my current career.
...
I did not wish to imply that your background was strictly academic. If it sounded that way, then I chose my words poorly. My apologies for that.

Through my specific (unfortunately necessary at the time) experiences, I happened to have stumbled across some instances where I figured out how to get good results from welded bolts. I did go through a fair amount of trial & error before getting it right.

It sounds like your hands-on experience went in a different direction. I am completely unfamiliar with the process of pattern welding. My knowledge of generalized blacksmith work is not much better. It sounds like you have done some interesting stuff.

As I said before, the points you brought up were all valid. You obviously do know what you are talking about. I may have come off as being more argumentative than I had intended to be. I have a bad habit of doing that sometimes.

I do agree that at this point, the conversation has become academic, which I don't necessarily see as being a bad thing. I like having my statements checked by knowledgeable individuals. It helps me to find inaccuracies & holes in my knowledge base, so that I can then have the opportunity to repair them.

Thank you for the cordial & enlightening conversation.

Jim
 
  • Like
Likes: Alan Gomes

leo310

.
Dec 15, 2006
455
Catalina Catlina 310 Campbell River BC
If you have 1 failed then I would replace them all. You could keep the others as spares. May cost you some boat bucks but then what doesn't.
 
Dec 27, 2012
585
Precision Precision 28 St Augustine
Update: The boat is now on the hard. I’m definitely replacing all of them. I took a close look at all of the mounts and realized One of the rear mounts was also broken. Currently I’m deciding between Westerbeke mounts (800. For all 4) or mounts through PYI inc (350 for all 4). This will be my winter project. My engine area is very tight. It’s almost like my boat was built around the motor. There will be a lot of cursing but the job will get done.

Once I replace the mounts I’m planning on paying to have the motor aligned. I would rather pay a few hours labor for the alignment then 10 hours for the entire repair.

Thanks for all of the advice
 
Aug 22, 2017
1,608
Hunter 26.5 West Palm Beach
What do those two different mounts look like? What do they have for alignment adjustments? For $800, I might consider making a set of custom mounts with integrated alignment adjustment slots if the factory original parts didn't offer me all the advantages that I was looking for.
 
Dec 27, 2012
585
Precision Precision 28 St Augustine
I ended up ordering the set from PYI for $350. They have a different look from original but offer the same lateral and vertical adjustment. The stud size is the same as well as the mounting holes. I contacted them before ordering. The staff was very knowledgeable and helpful.
 
Mar 20, 2016
500
Beneteau 351 WYC Whitby
I noticed you have a westerbeke . The motor mounts are prone to cracking at the 90 degree bend and breaking off.
In the last year I have welder 3 of these for other people in our club. Before they break ,what I have done when I welded them was added a gusset on the inside of the bend making they stronger,I actually have one I just welded in my garage and repainted
 
Jan 4, 2013
253
Catalina 270 Rochester, NY
I changed my Westerbeke mounts 2 years ago. It wasn't hard. The easiest way is to pull the engine bracket off the engine and then change the mount. This way all you have to do is support the engine, not jack it up.
 
Dec 27, 2012
585
Precision Precision 28 St Augustine
I just wanted to update this thread.

It’s rare that a project goes easier then expected but this one did. It took 4 mail order attempts to get the correct mounts but that was the hardest part. I utilized a members suggestion on raising the motor. Due to limited access below the motor and no way to raise it from above, it was suggested to place a deflated soccer ball under the engine and inflate the ball. Great idea, worked perfectly. I preset the mount height and installed within a few hours.

My marina estimated 1.5 hours per mount at $110 dollars an hour. Nothing better then saving money and gaining knowledge at the same time.
 
  • Like
Likes: Michael Davis
Aug 5, 2016
25
Catalina Capri 22 Cambridge
The studs can be replaced on my mounts. Not sure about yours. It looks like the adjustment is near the max height. That's not good. Better to shim under the mount than extend to max eighth.