Yanmar 3GM30F. Noise or Vibration

[EPRIMA14]

I have a Yanmar 3GM30F engine in a Hunter 356 with approximately 350 hours. From the beginning the engine emits a buzz between the certain some rpm. Initially it was vibrating between 1700 and 200 rpm with a 2-blade propeller. Now with a 3-blade propeller it vibrates between 1500 and 2000 rpm.
I have spoken with a mechanic and he comments to me that all the engines have an interval of revolutions in which works "forced" (stress point), but he does not give it a lot of importance. Is someone experienced of this topic?

 

[Alan]

The 3GM30F is normally a very smooth running engine. Any imbalance in the drive line will create a vibration which will most likely occur at certain rpm's. Because you've had a problem with this from the beginning I would start with checking engine mounts and shaft alignment. Be aware that shaft alignment cannot be done out of water and the boat must have been in water for at least a few weeks before it is done.

 

[EPRIMA14]

Thanks Alan. I checked the engine mounts and They seem correct. I have forgotten to indicate that the boat has a Saildrive SD20 Yanmar. Is it possible to have a problem with the saildrive alignment? The mechanic said me that it is better not to work in this "stress point", increasing or decreasing rpm until stop the noise.

 

[Paul356]

I've had a variation of this, with some of the same "chatter" in flat water motoring. When motor-sailing on starboard tack (boat heeled to the left), it's worse. When motor-sailing on port tack, heeling right, it goes away and that baby just hums. And if the boat is rocking side to side, the chatter comes and goes accordingly. Thoughts?

 

[Jim Seamans]

This is interesting. I didn't know the sail drive was available in the H356. Was this an after market install by previous owner??

 

[Alan]

Jim, I believe saildrive is standard on European boats.

 

[Alan]

Paul, can yo go below with someone else driving to try and get a sense of where this sound is coming from? There is a device called EngineEar which allows you to attach sensors to various components and allows the operator to listen to those components and help isolate the noise. You could also use a stethoscope in a similar fashion by using a long thin probe attached. You can buy one of these in most auto parts houses or tool distributors.

 

[Bill Roosa]

Welcome aboard

to the wonderful world of 3 cylinder 4 cycle engines.
There is a reason you don't see 3 cylinder engines in cars (except Yugo which is made in France I think)
For a smooth combination of rotating parts and power strokes you need either a 2, 4, or 8 cylinder engine. Even the 2 cylinder has some problems as either both pistons are moving up and down together and a power stroke every revolution or you have them moving in opposite directions and two power strokes one after another and then a pause of one revolution.
3 cylinders is just not a great mechanical idea IMHO No way to make the pistons and the power strokes work to make a smooth engine.
Trust your mechanic, he sounds like he knows his stuff.

 

[CaptainJB]

356 Vibration

I would have someone, a very good mechanic check it out.

The Yanmar engine in my 2002 356 suddenly blew an oil seal with less than 1200 hours on it. There was no warning, just poof !

Between the costs of removal, shipping, etc, a financial analysis justified replacing the engine at a mere $9,000.00

Investigate the noise vibration/noise very carefully

 

[Rick]

Re: 356 Vibration

Has your rig been tuned recently. That is a frequent reason to tweak the engine alignment. Run your engine in idol throughout those rpm ranges and pause in your area of vibrations. If its ok, then as said above, tis probably in the drive train. Sail drives on a 356. I'll be dam#ed! But if you havent had a grounding, ie sudden stoppage, it is most likely the prop, prop, prop. Borrow another three blader if you can before expensive probing by a mechanic.

Good luck

 

[Dan Johnson]

Bill R...

I hate to be contradictory, but check your cycle of operation for two and four stroke engines and I think you'll find that they do not operate the way you suggest.

Two and four cylinder engines pair piston strokes in 180 degree opposition. In four cycle operation on a four cylinder it takes two revolutions to complete a firing cycle, with each cylinder firing a half revolution apart.

Two strokes do it in one revolution, with the two cylinders firing 180 degrees (again, a half revolution apart).

PS: Early Saab 99's were three cylinder cars, all-be-it two strokes!