3GM30 Vibration and noise

[Trident]

I have a 3GM30 raw water cooled engine of unknown age - it has no numbers anywhere.

I have no idea of hours but since I bought the boat its been well maintained and had new water pump and exhaust manifold and elbow and new external oil pipes and been flushed, rust treated and repainted.

It starts first time every time, runs well, and makes no smoke etc

What it does do however is make incredible noise and vibration between idle and about 1500 rpm. At around 1500 rpm its still loud (its set in the cockpit in a nacelle on a cat so not tucked below deck in a room like on a monohull) but the vibration goes away and its smooth running all the way through from there.

I fitted all new engine mounts last winter to try and damp the vibration (made no difference) and sound insulated the engine compartment but at low revs it shakes the whole boat. I can find nothing "wrong" with the engine. So is this normal for these (not had one on any other boat) or can anyone suggest what might be out of true or need looking at?

Thanks

 

[geem]

Have you got the correct engine mounts? I had the 35hp in my Prout nacelle but never experienced this problem. My engine was old and raw water cooled but with correct Yanmar mounts was not a problem. They are very soft mounts form memory

 

[Trident]

Hi Tim, yes they are the R&D versions of the engine mounts but definitely the correct size and hardness (on the second try) for the 3GM30. I've only read good things about R&D but if we find nothing else maybe I'll sell a kidney and buy the genuine Yanmar mounts instead...

 

[Halo]

I think Yanmar engine mounts are very soft so it could just be a resonance bveing much more obvious with new mounts. I dont think you need to be below 1500 for much of the time in use so perhaps you could live with it?
The only other thing is that most engines have a damper on the clutch plate. It could be this is the problem. Others will know more about this than me.