Yanmar Vibrations?

[samdale]

I have a 1999 Beneteau 36CC with a Yanmar 3GM30F.
The boat has a pronounced vibration (hammering or thumping sound) at 1800 rpm, it is good at 1600 and returns to silent at 1900-2000.
It also makes the same thumping or hammering sound when going from neutral to forward.
The engine runs without any noticeable vibrations any where else from idle to full throttle.
I had the cutlass bearing replaced in february of 2009.
The shaft shows an out of balance rotation at this same rpm and by applying some pressure to the shaft it reduces the sound and vibration.
The engine mounts appear to be in good shape and adequately torqued.
My diver reports that there is no or at the most very limited play in the prop shaft, he feels well within specs and reasonble.
Any one out there have any ideas or possible solutions?

 

[alexco38]

Check and adjust the valve clearance. One (or more) cylinder is not working the same thus less power then the rest creating vibration. Either the owner manual or the shop manual should tell you how to adjust the valve clearance. Pretty easy job.

 

[sailaway78]

First determine

You need to first determine whether this is an engine vibration, or a driveline vibration. Does it do the same thing in neutral as when it is in gear. From what I read in your post, my suspicion is that you have a driveline vibration. Not sure what you mean by " out of balance rotation" but that certainly sounds like a good starting place. It only takes a tiny bit of out of balance to feel a noticable vibration. Second place to look would be the motor mounts, but first find out whether it is engine or drive line.

 

[BobM]

Its not unusual for a drive line to have a harmonic vibration at a given rpm. Just avoid that rpm. Did you perform an engine alignment when you did the bearing?

 

[Ross]

Bent shaft?

 

[Snotter]

What is the distance between the shaft coupler and the front of the stuffing box? Perhaps you need an additional bearing. If the distance is short, try aligning the engine to the shaft.

 

[shemandr]

Did the beginning of the vibration coincide with the replacement of the cutlass bearing?

 

[Richard Bryer]

I have had a very similiar problem with my 3GMF for several years. It only happens when the engine is hot- ie when we come in to the docks and throttle down to low speed then pick back up to ~2000. One of the suggestions was to make sure that your shift linkage was adjusted right so that the shift leaver is pushing all the way into forward (in this case)

 

[Don12364]

It Could be This

Do you have a dripless stern gland or similar? It is not unknown for the prop shaft to come into contact with the inside of the log tube at certain revs and this causes a loud knocking.
It can also occur with the conventional packed types of stern gland but, in this case, the stern gland acts as a journal for the shaft which is partly supported by the rubber tube between log tube and the gland.

 

[Rob & Rita]

Re: It Could be This

Our Hunter 356 with the 3GM30F had more of a shudder at startup, shutdown and when shifting between forward & reverse. This got worse after installing a high output alternator (110 amps). So, after talking to our local Yanmar mechanic, he asked without hesitation, what the idle speed was. He said the speed should be bumped up to at least 900 rpm's - my engine was set at 600 rpm.
After the idle adjustment, everything is perfect, smooth shifting, starting and shutdown (easy fix). Afterwards, I checked the motor mounts and found movement on lag bolt washers and one motor mount, rear portside top stud nut was loose. So, of course, a coupling alignment was required, which I did - alignment was out .010.
I've always had a slight vibration at 2300 - 2500 rpm which still exists. I just avoid that rpm range as suggested by other owners.
Good luck.
Rob Taylor - Raven I

 

[Mike B]

Assuming your prop is not out of balance I would check the shaft alignment first. It's a good start in addressing the RPM vibration, especially if it's not been done since the cutlass bearing was replaced. For the hard engagment of forward make sure your idle speed is properly set.

 

[Mike Holibar]

I have the same issue on my Rasmus 35 - 3hm30. In my case the solution Snotter suggests would be the answer. There is over a metre between the stern gland and coupling and an intermediate bearing should really be fitted. However, lazy as I am, I deal with the problem by avoiding the critical speedsm which are between 1000 and 2000 rpm.

Regards,