Yanmar 3YM30 Vibration at 2100RPM

I have a Beneteau 343 that I have bought from Sunsail, ex charter boat so the engine a Yanmar 3YM30 has done a few miles. It starts and runs fine with no smoke. The problem is at 2100rpm it makes the boat vibrate badly. I have checked the prop alignment and it was slightly out, I have adjusted it and I think it is well within tolerance. There is no play in the cutlass bearing. The 2 rear engine mounts are a bit soppy but I dont think they are the problem. When the vibration occurs there is no noticeable movement on the engine. Before I tried the boat in the water it was lifted out for antofouling etc, while out I could not see any obvious damage to the prop, it has 2 fixed blades. Difficult to tell at 2100rpm wether there is any misfire. With prop disconnected there is no vibration but then it is not under any load. I am now retired but was a car mechanic for most of my life. A bit stumped on this one. Any Suggestions greatly appreciated. Ray

Has it had the vibration since youve owned it? When you say sloppy engine mounts, what does that mean? if they are moving up dow or side to side too much when UNDER LOAD, it will cause the alignment to be thrown off and massive vibrations can occur. What kind of shaft seal do you have? does i leak more with vibration? and can you rotate the shaft by hand with the engine off?

buick430 said:

Has it had the vibration since youve owned it? When you say sloppy engine mounts, what does that mean? if they are moving up dow or side to side too much when UNDER LOAD, it will cause the alignment to be thrown off and massive vibrations can occur. What kind of shaft seal do you have? does i leak more with vibration? and can you rotate the shaft by hand with the engine off?

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Hi Buick 430

I bought this boat on the recommendation of some one I know in Greece. With hindsight not the smartest thing I have ever done but not the dummist either. The vibration was there there the first time I took the boat out. Since my last post I have done further work and this is now where I am.
In neural the vibration would start at 2100rpm and disapear over 3000rpm.
In drive the vibratin is there from 2200rpm upwards.
On checking the eng mountings I found thr rear starboard one had a definate clunk when lifted and dropped back down.
I replaced this one and the vibration in neutral has disapeared and the vibration in drive is less but its still not as it should be.
When I described the eng mtgs as soppy I meant thee was some movement but not excessive. The deflection on a new mounting is shown as 4.7mm, I measured mine amd they are at this figure as best as I can measure the lift. Shaft turns freely in neutral with no tight spots. When the vibration occrs in drive there is a very small amount of movement on the mountings, the same amount on the new one as the old ones, this is a 3 cylinder Yanmar not a rolls royce I wouls expect a small amount. My dilema is I could replace the other 3 engine mountigs but they cost 220 euro each with no guarantee of curing th problem.