Does your Yanmar 3GM vibrate?

[tomgrigsby]

Mine does. Previous owner said it vibrated. Did an alignment but it measured pretty good. I've lived with it for a few years thinking the shaft was bent. Just replaced shaft and it's better but vibrates enough to shake the lifelines under high load. Anyone have similar problem and a successful resolution?

 

[Michael Davis]

If you've changed the shaft and cutlass bearing then motor mounts and propeller are all thats left. I assume it runs smoothly in neutral? If the shaft was bent could the prop have been damaged?

 

[PaulK]

Ours vibrates; why would it not? If it's too much I'd second Michael's suggestion and perhaps have the prop rebalanced and get new motor mounts.

 

[Bill Roosa]

ANY 4 cycle engine with only 3 cylinders is going to vibrate at low RPMs.

 

[ggrizzard]

"Does your Yanmar 3GM vibrate?"
Only when I put in quarters!

 

[NYSail]

All relative.... though if it shakes the life lines you may have a problem. High RPms mine gets real smooth.... loud but smooth. Have to watch engine. Maybe a broken mount.

 

[LeslieTroyer]

my universal M25 idles very smooth - its a three cylinder -

 

[nveater]

Mine did although it would smooth out at top rpms- this winter I had my engine removed for servicing and my boat yard guy told me the engine was misaligned- so I figure cool problem solve should cut down on vibration- Then my engine guy says bad news you have a bent connecting rod because one the cylinders got water into it and caused hydro lock- so I am curious to see how smoother the engine might be

 

[rardiH36]

Not yet mentioned in this thread. But what I have read about. And what I noticed did improve (but didn't completely elimnate) the rough vibration of my 1979 2 cyl Yanmar 2QM20.

That is the condition of the fuel delivery "piping" to the engine:

If one has a very small crack in the fuel line hose, or if a fitting isn't right, just a small amount of air can enter along with the diesel. Not enough to cause the engine to stop running. But enough to cause a cylinder to sporadically misfire. Or if one of your 3GM's three fuel injectors is malfunctioning a bit, the corresponding cylinder will fire with less power. Or intermittently. The explosion unbalance between the cylinders can cause vibration.

My experience goes back five years ago. I let my diesel tank level get a little too low. 25%. In a swell, the engine sucked air. Stalled. Wouldn't start again without bleeding. Fortunately I was able to sail to a calm spot. Got the engine going again. Aside from now never letting my fuel level go below 1/3 full, the episode prompted me to do a long overdue replacement of everything in the fuel delivery system between the fuel tank and the injectors. Except I didn't do anything to the low and high pressure pumps. New hoses and new banjo washers. Afterwards, my engine ran noticeably smoother. Although, being a 2 cylinder, it still bangs around quite a bit! I suspect that I was sucking a bit of air before.

 

[tomgrigsby]

Mine only vibrates significantly under high load forward. Full reverse is smooth as butter. This seems to me to indicates two things; one, prop probably isn't out of balance, and two, it's only higher load in forward due to prop more efficient in forward. I've considered changing the motor mounts, though tired out, none seem to be broken. What makes me hesitate is that I've read threads where most said changing motor mounts didn't really improve things all that much. Man I hate to spend between $300 and $600 dollars with no improvement. In replies above, one 3GM owner says his does vibrate, and the other says his is smooth under high rpm. Obviously I don't know what's wrong, if anything, and I really appreciate all the suggestions and having taken the time to reply.

 

[Michael Davis]

If your mounts are tired then replacing will make some difference, as will going to a 3 blade prop. All depends on how much it bothers you. A boat is a boat but money is only paper!!!!