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Old 01-13-2017, 09:59 AM   #1
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Engine Mount Question

The mechanic who surveyed my new to me AT 34 recommended changing the rear engine mounts on the Cummins 330 hp engine. The boat is 13 years old. and has a bit of vibration at higher speeds. For not much more money I could change all 4 mounts, even though the front mounts seem fine. Opinions? - Is it worth doing all 4 at once?
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Old 01-13-2017, 10:42 AM   #2
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Knowing nothing about the mounts used I would suggest that if you are changing the rears it is time to consider fronts as well. I like to think of it as one thing less to worry about and they are aligning the engine anyway...
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Old 01-13-2017, 10:48 AM   #3
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Change all four. If you are going to all that trouble, why not? Be sure to get someone who knows his shit to align the engine. With new mounts and properly align you will notice a difference.

Had a guy align a Cummins for me and when he finished it was so good that with the transmission in neutral and engine idling , the prop shaft would turn REAL slow. It took him four hours to get there. Good thing I was not paying by the hour and he was a perfectionist.
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Old 01-13-2017, 11:13 AM   #4
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It is always recommended to change all mounts when replacing. That way they age and perform same/same through their lifespan.

3 years is pretty new to be replacing mounts, natural rubber mounts should perform 10 years +

Typically a mount will fail prematurely from being contaminated, the one we usually see fail first is the one under the injection pump which has failed from fuel leaking onto it.

Pretty unusual to replace just the aft mounts because they have failed without reason.

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Old 01-13-2017, 11:16 AM   #5
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3 years is pretty new to be replacing mounts, natural rubber mounts should perform 10 years +
He's at 13 years, not 3. So replacement isn't a bad thing.
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Old 01-13-2017, 11:46 AM   #6
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Focus depends on coffee early in the morning, duh. Never mind



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He's at 13 years, not 3. So replacement isn't a bad thing.
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Old 01-13-2017, 12:12 PM   #7
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What is wrong with the mounts? The Barry mounts are pretty robust. And vibes at high rpm are rarely related to mounts. Poor mounts tend to shake the boat at idle rpm.

Pics would help.
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Old 01-13-2017, 12:22 PM   #8
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Always change them all , or you'll be back in a couple of years to spend all the cash to align the fronts.
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Old 01-13-2017, 12:34 PM   #9
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I would change them all.

But I would get a knowledgeable second opinion before I did anything.
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Old 01-13-2017, 04:38 PM   #10
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Looks pretty unanimous ... all four it is!
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Old 01-13-2017, 04:42 PM   #11
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I would change them all.

But I would get a knowledgeable second opinion before I did anything.


Get that 2nd opinion.

My mounts were installed in 1980. I repowered in 2000, at which point I had the mounts checked. Still OK.

I had the port engine out in 2014, checked again, still OK. Methinks there could, as others have suggested, be some other reason for your vibration. Mounts do not have a set expiry date.
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Old 01-13-2017, 05:04 PM   #12
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Get that 2nd opinion.

My mounts were installed in 1980. I repowered in 2000, at which point I had the mounts checked. Still OK.

I had the port engine out in 2014, checked again, still OK. Methinks there could, as others have suggested, be some other reason for your vibration. Mounts do not have a set expiry date.
No expiration date, but that is very long time for a set of mounts designed and made in 1980.......

Who is saying they are OK and to what criteria?


While a agree to a point...this quote seems to be a pretty well spread idea by a lot of people in the business...


"If your engine mounts are more than five or six years old, or have been contaminated with seawater, engine oil or coolant, change them.


Replacing engine mounts - Ocean Navigator - November/December 2012
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Old 01-18-2017, 07:54 AM   #13
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5 or 6 years old is a little premature for replacement due to just age. This is what an natural rubber mount manufacturer says about mount lifespan:


The life expectancy of the rubber elements will be approx. 20 years in ideal circumstances. Unfortunately ideal circumstances are not feasible, therefore the (working) life expectancy will be approx. 10 years. The life expectancy of the rubber elements is dependent on the environmental circumstances (weather influences, contaminants, etc).




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No expiration date, but that is very long time for a set of mounts designed and made in 1980.......

Who is saying they are OK and to what criteria?


While a agree to a point...this quote seems to be a pretty well spread idea by a lot of people in the business...


"If your engine mounts are more than five or six years old, or have been contaminated with seawater, engine oil or coolant, change them.


Replacing engine mounts - Ocean Navigator - November/December 2012
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Old 01-18-2017, 08:28 AM   #14
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Agree....different types of isolation mounts could be quite different, plus their operating environment.

Like many things on a boat, the time to replace is when the object is no longer capable of doing its job or might not be when you are someplace the fix would be more trouble than early retirement of the object.
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Old 01-18-2017, 09:27 AM   #15
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Many mounts have a visual tell-tale that indicate whether it has collapsed or is overloaded. Many surveyors don't know how to actually check. And many do not understand vibration dynamics of engine/drive systems and can lead to misdiagnosis.

That was the basis for recommending a little more looking before replacement.

Photos would help in the OP's case.
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Old 01-18-2017, 09:34 AM   #16
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Is it possible the other two mounts had been changed recently? Seems odd a mechanic/surveyor would recommend only changing the aft mounts.
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Old 01-18-2017, 09:37 AM   #17
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Engine mounts seem to me to be like injectors: often replaced and don't solve the problem. Listen to Ski and evaluate further before replacing.

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Old 01-18-2017, 09:55 AM   #18
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Ten years ago Yanmar recomended replacing their very soft mounts every year or two. Being so soft probably has a lot to do w it but that's just a guess.
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Old 01-18-2017, 10:59 AM   #19
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Quote:
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Ten years ago Yanmar recomended replacing their very soft mounts every year or two. Being so soft probably has a lot to do w it but that's just a guess.
Eric:

I suspect that Yanmar's recommendations had more to do with their bottom line, than their customer's satisfaction. Those Yanmar mounts cost double what Barry mounts cost.

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