engine vibration problem

Posted By: Craig Hershoff
Date: 2/1/08 6:41a.m.

Report: outside forum guidelines

I am hoping that someone has some experience with engine vibrations. My 1991 Arctic has a 9 hp Yanmar diesel. It has had a vibration problem since I bought it 3 years ago. The engine runs smoothly at higher speeds (over 2200 rpm). At lower speeds, in neutral gear, it shakes a little, probably due to the inherent properties of a single cylinder engine. When in forward gear, at speeds between 1000-2000 rpm, it goes in and out of a sometimes-intense vibration mode. This doesn't happen at all in reverse gear, or in forward at high speed. I had the prop checked, and it is good. When I hauled the boat, I noticed that the cutlass bearing strut that holds the propellor shaft was bent slightly to port, and the shaft was not centered in its entrance hole into the hull. It was flush against and rubbing the starboard side of the hole (stern tube). The engine mounts were 16 years old and supposedly should be changed every 3 years according to Yanmar, so at $90 each I replaced the 4 mounts, trying to keep the alignment of the engine the same as I thought it was when first installed. This eliminated the vibration almost completely, until I had to put the engine in reverse and give it a lot of power. After that, it started vibrating badly again in forward, at low speeds, even after re-tightening the mounts. Other than getting a bazooka and blowing it up, does anyone have any suggestions? I thank you for reading this long message and for any helpful advice Craig Hershoff, "Gypsy Rose"