Winter Projects 2013 – Part I

There are little secrets on every boat.  They’re secret because they are hidden from view and easily ignored, and because they are things we boat owners don’t want to think about.  Why?  Because these secrets are maintenance or repair issues that are costly to resolve in terms of cash (if you pay to have this sort of thing done) or effort/time (if you do it yourself) or both (parts can be pricy).  I’ve got a few secrets I want to shine the light of day on and resolve this winter.  What follows is Part I of a four-part series unveiling my little secrets – and forcing me to address them.

Secret Number 1:  Motor mount lag bolt loose

Background:  I paid to have a new motor installed in spring of 2006.  This Yanmar 2gm20f almost directly replaced the old 2qm15.  I say “almost” because there were adjustments to be made in the mounting, but it was pretty close.  I paid a re-power engineering company to do this work, and now wish I’d paid the yard – Sadler Point Marina and boatyard.  Chip is the boat tech I would have wanted to do the work.  He is, simply put, incredibly skilled and thorough.  However, I did not do that.  I contracted with the engine supplier/marine engineering firm to do it (who shall remain nameless), and I got mixed results.  Two of the projects that I detail in this series directly relate to the quality of installation I received.  Okay, on to the “secret,” but first, a photo:

Starboard aft engine mount. Aft lag bolt.

Click the image to get a better view.  The red arrow and circle mark the bolt.  As the caption describes, this is one of two lag bolts that hold the engine mount in place.  Less than a year after the engine was installed, I noticed that this lag bolt was vibrating while the engine was running.  It should not vibrate. Everything above this bolt can vibrate, but not the bolt itself.

I explored the situation with a socket wrench, and discovered that the bolt wouldn’t pull down. Hmmm. . .   My jury-rigged way of addressing the situation at that point (I’ve come a long way in DYI projects since then), was to install a larger lag bolt into the hole, and bed it in 3M 5200.  It pulled down tightly, but it kept nagging my conscience.  Now I notice that this bolt vibrates as well, but I don’t know how long it’s been loose.  What to do?

Obviously, the engine mount has to come off the bed.  Then I need to determine how far the rot extends in the engine bed.  Following that, I need to remove or treat the rotted wood, replace or repair it, then reinstall the motor mount.  There are at least two avenues of approach: 1) over-drill the hole until I find solid wood, then fill with thickened epoxy.  I can probably tap the newly filled hole, and install a machine screw to hold the engine mount, or 2) remove all the rotted wood and epoxy a new section of wood in its place.  Then drill to size, and install the engine mount again with a lag bolt.

All conjecture at this point – I won’t really know how to proceed until I get into the project.  Any other ideas or experiences you can share with me are very welcome!  Just make a comment in the comment section below.

  1. Jan Sopoci said:

    Just a guess on my part (obviously), but I suspect it unlikely that your first option/suggestion (drilling over-size until reaching “solid” wood) seems fairly improbable. The ear/tang where the bolt hole resides isn’t all THAT big.

    • I don’t know, Jan. The bed is probably 3.5 inches at that point, and the bolt-hole is about .5 inch. I can imagine (!) that the hole is only enlarged by rot, and easily drilled over-size. This is purely speculation, though. You’re right, I should expect a worse-case senario.

      • Jan Sopoci said:


        My comment was based on the likelihood that the condition has been present for quite a while, leading to rather extensive rotting/softening of the wood. Maybe fortune will smile on you!!! ;-)

      • That’s what I expect too. My view is overly-optomistic. What I expect to find is a large section of rot that has to be excised and replaced with a sizable piece of new material. But, I love epoxy – it’ll stick a new section in place permanently.

  2. Jerel David Dawson said:

    have already had this experience..”dug out” the hole with 1/2″ wood bit..filled with epoxy resin and teak wood saw dust from my shop..redrilled the the lag bolt with the same epoxy far so good!!

    • Thanks for sharing that experience with me. It gives me hope that it won’t be such a major piece of surgery after all.

      What Kind of boat do you have, and how was your access to the engine bed?

      • Jerel David Dawson said:

        rick..i have a 1980 w27cb..removed, painted the mounting brackets and changed all my mounts by unbolting the coupling then “blocking up” the engine..discovered the “bad holes” when installing the new mounts..expanded the engine access hatch this “fat man” can get in all the way to the top of the fuel tank

      • That was a big job, Jerel. I’m thinking of doing my one mounting hole exactly the same way: Block that side of the engine, remove the mount, operate on the bed, reinstall the engine on the mount.

        Did you have much trouble re-aligning the engine and coupling? Any advice about doing that you can offer would be appreciated.

  3. Jerel David Dawson said:

    no that big of a job..their are several online tutorials on engine alinement..not at all difficult..btw something that should be checked periodically..a mechanic friend of mine advises against changing just one mount..either change fronts or rears or all!

    • I don’t think I need new mounts. I just need to make sure that they are securely attached to the bed and the engine! The mounts were new when the engine was installed in ’06. Glad to hear you think it’s simple – you’re probably a mechanical engineer, though :-).

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