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I currently have a Boston Whaler 31L, with twin Cummins 6BTA’s. I’m looking at buying a Mainship 34 Pilot with twin Yanmar 4LHA-STP’s, with 1100 hours on them. When I took it out for sea trial, I noticed that the Yanmar engines vibrate a lot more at idle than my Cummins engines. They are smooth running at cruising speed. This is my first experience with the Yanmar engines, and I was wondering if it’s normal? I know the 6 cylinder Cummins engines have a heavier flywheel and engine block, versus the lightweight 4 cylinder Yanmars, and I suspect that it helps to dampen the vibration. Also, any thoughts on the Yanmar 4LHA-STP’s? I know Yanmar engines have a good reputation.
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I think Yanmar typically uses softer engine mounts than Cummins. If there is any inherent vibration the Yanmar will tend to rock-and-roll a bit more, while not transmitting that motion as strongly to the boat.
I had Yanmars for years before the Cummins I have now.
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Vessel Name: Tenacious
Engines: 6BTA 5.9 330's - "Seaboard Style"
Location: Long Island, NY
Country: USA
4 cylinder engines have an inherent vibration, do not compare to your 6 cyl and think your are comparing apples for apples. May be able to be improved with updated isolator mounts, such as the new SMX mounts with 40 or 50 durometer inserts.
The Yanmar 4LH is a desirable engine and was a super engine the day it left the factory X number of years ago. It’s what has been done to it (or not done to it) since that day as to what matters now…..
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