Engine mounts - replace how often

[preserved_killick]

How often do engine mounts require replacement? I've been told "every few years" and I know lots of people who never replaced their mounts, and have a smooth aligned engine regardless. Vetus (my engine) does not publish a timetable for this that I can find.

My boat has a 10 year old Vetus diesel with low hours (less than 500). After getting a coupling issue straightened out, I realized that my engine was in badly in need of alignment. After much fuss, I've got it much closer, although it not perfect yet.

Now, I'm wondering why my engine alignment was so far off. When I got the boat the drive train was very smooth in operation, which I later learned was because the flexible coupling was purposefully setup to be loose, which is not a recommended install according to Vetus.

Of the two likely scenarios I'm thinking the first is the most likely :

1. Engine was not aligned correctly from the beginning, and the coupling setup masked the issue.
2. Engine was aligned properly 10 years ago, and perhaps the mounts compressed over the years and threw the alignment off, and previous owner just loosened the coupling instead of fixing the alignment.

So, my question is.. how do engine mounts wear? Do they compress, compress unevenly, become brittle? How long can they last? Do they wear from age, or vibration?

Cost? I checked with Vetus, and it looks like each mount is $160! Some maintenance items I'm willing to replace on a schedule, regardless of wear, but for $600 I need a good reason to do so!

-jeff

[Tim]

Yes, they all wear and lose their resiliency over the years, but there is no hard and fast rule. Basically, they need to be replaced when they need to be replaced. Each type and manufacture of mount is different in its construction and longevity, but none are designed to last forever. That said, you see plenty of situations where the mounts have never been changed in 20 or more years; this doesn't mean it's right, but there you are.

They should easily last 10 years if the engine installation is decent- (even the super-soft, rubbery, known-for-compressing-over-time Yanmar mounts will last this long, though that's about it), but one should always be looking for signs of compression, rubber brittleness or failure, and lack of proper support (such as misalignment problems, excess vibration, etc.)

[Rachel]

Hi Jeff,

Coming from the other side of the mounts, do you have the original "first generation" A-30 engine beds? That is, the ones that were designed for the Atomic Four? If so, they could be contributing to your problem.

They looked like this in A-30 #221 (just peer through the tangle). They're basically just hollow angle shapes of fiberglass, tabbed to the hull on the inner sides, but with no special support on the outer/upper side of the angle.



The reason they could be a problem is that they were relatively un-sturdily built. That is, they were perfectly adequate for the A-4, because it is so smooth, and, as I understand it, does not give the beds much of a work out. But I've read (and wouldn't disagree), that they should not be used to support a diesel engine, because it does move around more and with more force. I could easily see them flexing or distorting under more of a load.

If your boat originally had the Greymarine gas engine (used in earliest boats) then I'm not as familiar with the beds, but I suppose something similar could be the case. Here's a photo of what I presume are original greymarine beds in an A-30 I looked at (yes, Britton, it's the infamous one near your place) (that I backtracked ten hours to look at and only realized as I pulled into the driveway that it was one Britton had previously looked at and told me about just two days before).



Of course if your beds have been rebuilt, then... never mind! :)

Rachel

[preserved_killick]

Hmm, I don't think they look exactly like either of these, I don't think that they are hollow..but then I never suspected this could be the case. I've saved your pics and can zoom in w/photoshop. I'll take a closer look when I go to the boat this week.

Thanks Rachel.

[ddsailor25]

I ran into this problem when we replaced our A4 with a diesel. I didn't realize that the beds needs to be replaced until I started the new engine and got her in the water. Diesels have enough torque and vibration to torque itself out of alignment under load on the orignals A4 engine beds. So the next season I pulled the engine and rebuilt the engine beds with white oak. She is solid and there is no deflection or alignment issues under any load.

Dave