Hunter 29.5 2GM engine vibration

[Brian M H23]

Hey all. I poked my head in here last fall. Proud owner of a 96 29.5, bought right before haul. Very little "running time" besides a quick runabout, and I assumed there would be drivetrain work agreed purchase. After winterizing and a cutless bearing /packing gland rebuild, were back in the water!

I don't have a very good baseline (and the cutless was completely shot), but the vibration in gear, engine movement seems a bit excessive.

As a non marine guy, I'm leaning engine mounts - they are *very* soft — but figured I'd ask for some input. What do you think?

VID_20250512_151624697.mp4

drive.google.com

 

[Ralph Johnstone]

What do you think?

I think it looks like someone doing the beer barrel polka.

I'm leaning engine mounts - they are *very* soft

Very true but something else is "causing" the engine to shake severely fore and aft. I've noticed on my 2GM20F that engine vibration is a slight rotary movement for a degree or two CW and CCW . Not a fore and aft movement. The up and down movement of the pistons causes the slight rotary movement but I'm not familiar with what would cause the fore and aft movement as seen on yours.

Also noted in this vid. of the engine in neutral is that the X-mission flange is slowly turning. Somethig else to question. Usually the coupling doesn't rotate in neutral.

It'll be interesting to see any other ideas on what's happening here.

 

[Ralph Johnstone]

Are your mounts down to 3/16" yet ?

 

[Brian M H23]

They're probably the original mounts from 1996... If i had to guess. The last owner had it 15 years and didn't do much of anything in this department as far as I can tell

 

[BigEasy]

I replaced engine mounts a few months ago on my 3YM30 Yanmar. Excessive vibration in neutral idle, but not as bad as seen in your video. Huge improvement with very little vibration remaining. Be aware that Yanmar mounts will cost over one boat buck. I replaced with Ellebogen mounts from Spain at half the cost of Yanmar. Excellent product & customer service. Regardless of manufacturer, you will need to determine the rating of the rubber mounts for your engine. Mine had a rating of 100 for forward mounts & 75 for aft mounts. You should be able to determine that info in owner‘s manual or the numbers should be embossed on the outboard rubber surface of the mounts. See @Ralph Johnstone photo for rating number location.

 

[Ralph Johnstone]

Excessive vibration in neutral idle, but not as bad as seen in your video.

I don't want to get ridiculously nit picky here but ...................... is there any chance you noticed the direction of vibration before you changed the mounts.
Fore to aft or more of a rotational vibration for a degree or two.

On rare occassions, I used to get into vibrational analysis on the job so littel things like this stick with me.

 

[Ralph Johnstone]

but the vibration in gear, engine movement seems a bit excessive.

Can you get another shot of the vibration with the engine in neutral but at higher RPM ?

 

[BigEasy]

any chance you noticed the direction of vibration before you changed the mounts.

No, unfortunately not. The mounts were 18 years old.

 

[Ralph Johnstone]

The mounts were 18 years old.

Mine are original 1998 mounts that feel as smooth as glass under power. They are all getting down to just under 3/16" and I'm getting ready to change them next winter.

Primarily because they're looking at 27 years old but also I have no other projects lined up for next winter. Gotta keep occupied somehow.

 

[BigEasy]

Mine are original 1998 mounts that feel as smooth as glass under power.

Mine were OK at cruising RPMs but too much vibration at idle & neutral.
Ralph, you got to be really bored to want to change engine mounts, because no other projects. It was brutal to change mine because of limited access. Very poor design by Beneteau. Took mechanic & me 20 man hours.........never again! But, it runs smooth now.

 

[Ralph Johnstone]

Ralph, you got to be really bored to want to change engine mounts, because no other projects. It was brutal

Bored to some extent but I'm really into masochism. Love the pain.

As part of the head games, I've already started photographing and marking which wires and tubes will have to be disconnected and removed. Once those are complete, next will be the best possible plan to replace the mounts so that I have the least amount of alignment afterwards.

It can't be that bad can it ..................... I did the aft starboard mount many years ago and what a bitch that was. And it was the easiest one to get to. I swore next time I dealt with supports, I would have it planned and photographed to the last wire and hose.

You know what they say, "best laid plans of mice and men ..................." :

 

[heritage]

I would check the engine alignment before changing motor mounts. Show us a video of the engine running while in neutral.

 

[Ralph Johnstone]

Show us a video of the engine running while in neutral.

I'm not clear on this one myself. @Brian M H23 has not replied on this item and in the VID. it looks like the shaft coupling is very slowly rolling over :

vid. it

Either way, @Brian M H23 , we can't go any further until we get a video with the engine IN NEUTRAL and slowly rev the engine up and down. It's almost certain to have been the cause of the damage to the strut.

Thanks. This is the most interesting case in quite a while.

 

[Panera]

Hunter 280 1997 - I replaced my engine mounts last summer, huge difference.

 

[Charlie98117]

I agree there could be an alignment issue but more likely one or more mounts are gone.You can check out the blog page on the Ellebogen site, there are a couple of 2GM20 case studies. They are also IMHO the best option for aftermarket Yanmar mounts. Blog US - Ellebogen

 

[Brian M H23]

I'm not clear on this one myself. @Brian M H23 has not replied on this item and in the VID. it looks like the shaft coupling is very slowly rolling over :

View attachment 231498vid. it

Either way, @Brian M H23 , we can't go any further until we get a video with the engine IN NEUTRAL and slowly rev the engine up and down. It's almost certain to have been the cause of the damage to the strut.

Thanks. This is the most interesting case in quite a while.

Ralph, engine was in gear in that shot, about 1200 rpm if i recall. I do have a video of idle but the vibration is less pronounced

I don't have much information prior to my work because all I ever did was motor it to haulout and a very short sea trial. I did very causally notice the mounts are rusty, ugly and very soft without knowing these are a common wear item. Next trip to the boat will be armed with new ones

 

[Brian M H23]

I replaced engine mounts a few months ago on my 3YM30 Yanmar. Excessive vibration in neutral idle, but not as bad as seen in your video. Huge improvement with very little vibration remaining. Be aware that Yanmar mounts will cost over one boat buck. I replaced with Ellebogen mounts from Spain at half the cost of Yanmar. Excellent product & customer service. Regardless of manufacturer, you will need to determine the rating of the rubber mounts for your engine. Mine had a rating of 100 for forward mounts & 75 for aft mounts. You should be able to determine that info in owner‘s manual or the numbers should be embossed on the outboard rubber surface of the mounts. See @Ralph Johnstone photo for rating number location.

I've got some conflicting information here... I made the decision to install #100 at all 4 corners, from what I understand the rear mounts are a tad soft OEM to allow for some "wiggle" under power given the solid shaft connection. RD marine (manf of the flex coupler I installed) would have you put their redesigned, much firmer design in place with a flexible coupler there

 

[BigEasy]

I've got some conflicting information here... I made the decision to install #100 at all 4 corners

I would stick with OEM configuration on the entire drivetrain, including engine mounts. Especially since You’re not sure of the before condition as pertains to the excessive vibration & cause. By deviating from OEM set-up you’re introducing more variables. You mentioned that the cutlass was “shot”; perhaps the shaft is bent or there is a problem with the coupling to shaft fit, engine alignment, or bent prop. I would have a machine shop check shaft runout & fit /face to a new coupling. Finally, why install the flex coupling? There is no sailboat manufacturer that installs them. I have no experience with the flex coupling; however, have read many times that all it does is mask an underlying problem. You might need to get a good/reputable marine mechanic to help sort out & fix the problem(s).

 

[Ralph Johnstone]

I do have a video of idle but the vibration is less pronounced

Once again, before you spend a nickel (wooden or otherwise) we've got to see a video at various RPM IN NEUTRAL. You're prop might, maybe, could be causing the vibration. So far, we have very little information and hence everything is a wild, guess.

We're just back to the same old SBO mantra here "Help us and we'll help you."

 

[Ralph Johnstone]

By deviating from OEM set-up you’re introducing more variables.

My good sir, I leave the positioning of motor mounts in your capable hands.

Based on specifications from both Ellebogen and Yanmar I offer the following :

Ellebogen

Yanmar Parts Catalogue

Purchase of Aft Starboard Mount in 2009
​

Check the parts numbers. My purchase in 2009 and the Yanmar parts catalogue show the same parts number. The Ellebogen parts numbers disagree. I am still looking for a paragraph in a Yanmar catalogue in which the Ellebogen and the Yanmar parts catalogue agree.

@BigEasy , I'm relying on you for the correct location of these mounts as I'm getting ready to replace the mounts on my 2GM20F with Ellebogen mounts next winter.

Please don't leave me hanging .