Motor Mount Wiggle

[Neo]

I am trying to locate the source of excessive vibration in my Yanmar 2GM20F.

I am replacing the cutlass bearing and having the prop and prop shaft checked at H&H but I am not sure how to check the motor mounts.

I don't see any cracks and when I lean on the engine to flex them, they seem to hold fast. See video link below.

Do they look OK to you?

Is there a better why to check them?

Thanks

https://www.youtube.com/watch?v=Zj5OsBBiiQA

[delmarrey]

When are you experiencing excessive vibration? While motoring, at an idle, high RPMs???

[Neo]

There is no vibration to speak of when the transmission is in neutral, runs smooth up to 3,000 rpm. But when under load, motoring, there are a few rough spots and a few sweet spots. In the rough spots the steering pedestal vibrates visibly.

[delmarrey]

In my case after a motor change I had a whipping shaft and ended up upsizing the shaft.

But it could be a number of things. You'll have to start with an inspection of the whole drive train. It could be anything from a sticky folding prop to the coupler out of align.

The motor mount in the video looks like it's in good shape but there was a lot of movement. For that same reason I installed a planetary drive (Pythondrive) so the shaft would stay straight in align at all times.

Yanmar mounts do have a scheduled replacement time. Stiffer mounts (after market) transfer the vibration to the hull.

[Neo]

I plan to have the prop shaft aligned with the transmission flange in the spring.

Not sure if the mounts being too flexible, but they do shed a lot of rubber dust on a regular basis.

[delmarrey]

Originally Posted by Neo

I plan to have the prop shaft aligned with the transmission flange in the spring.

Not sure if the mounts being too flexible, but they do shed a lot of rubber dust on a regular basis.

How old are they? I've never heard of that before but if you rub your finger across the mount and a lot black comes off on your finger, I'd plan a replacement on your next haul-out before the alignment. Are you sure it's not the alt belt dust.

Some Yanmar motors have two different mounts installed on a single motor. So check to make sure which ones go where.

Here's an aftermarket brand. Scroll down, it shows which original mount goes where.
http://www.pyiinc.com/images/pdf/rd/...R%20YANMAR.pdf

[Neo]

The boat is 26 years old. I'm pretty sure they are the original motor mounts. It is not belt dust. I assumed it came form the mounts, but I will double check next time I'm at the boat. It could be from the sound insulation.

Thanks for the link.

[Neo]

I took a look at the mounts in the link you posted. They mention an oil shield to protect the rubber element from petroleum degradation. That struck a cord. My lift pump had been leaking fuel on that mount for years before I purchased the boat. That might be why the rubber is breaking down. All the particles.

[hellosailor]

I've never heard of motor mounts being too flexible. As they age, they all get hard and stiff and the rubber companies will all tell you to replace them every five years. But they don't get more flexible, unless something outright cracks and fails.

Since the entire drivetrain is being redone and everything will need to be re-aligned anyway, this would be a good time to replace the mounts, especially if they are way more than five years old. Regardless of whether they have failed yet.

[roverhi]

Redid the installation of my 3GM using aftermarket mounts. The 9 year old Yanmar mounts looked good before pulling the engine but were falling apart when I inspected them after removal.

[Jacko]

Hi Neo had a problem with my 3hm Yammy years ago and you will probably find if you pull out your existing mount that you will be able to pull apart with you hands as the rubber parts from the steel after a few years use. I replaced with non gen mounts ( www.isoflex.com.au) and you wont believe the change. These units have been used for 2000hrs now and are still performing as day one. I am sure you will get similar units where you are if you google Cheers Jacko

[Wotname]

Wow, 26 years old and one diesel soaked - yes I would change them...

Be aware however, the 2GM20 motors will have some rough spots over the rev range, even with a very good installation. The actual revs where it vibrates excessively is installation / boat dependant. You just have to take note of your particular installation and then avoid operating in the "unsweet" spot(s).
This is mentioned in the installation/ operation manual.

For instance, mine gets a good (bad!) vibration around 2,500 rpm so I avoid operating between 2,200 and 2,700 RPM. Also a little bad around 1,000. Everywhere else is very smooth.

[Neo]

Originally Posted by roverhi

Redid the installation of my 3GM using aftermarket mounts. The 9 year old Yanmar mounts looked good before pulling the engine but were falling apart when I inspected them after removal.

In the video I was pushing on the engine really hard, with my feet braced up against the bulkhead, and the mounts held fast. Maybe that is why the mounts seemed excessively flexible. (The engine is really light). I am guessing they are in pretty good shape. Maybe they are not the originals. It is just that based on the lack of maintenance the engine has received overall, I assumed that they were.

I can get the Yanmar mounts for a little over $300 and the P.Y.I mounts for $100.

Might as well install new. It's just another $100...

[Neo]

I assume changing the mounts is fairly straight forward. Unbolt mounts, jack up engine a few inches, replace mounts??????

And make sure the front pair of mounts go on the front and the back pair on the back.

[Wotname]

Originally Posted by Neo

I assume changing the mounts is fairly straight forward. Unbolt mounts, jack up engine a few inches, replace mounts??????

And make sure the front pair of mounts go on the front and the back pair on the back.

AND re-align the engine. The new mounts aren't going to put the engine back into exactly the same position as the old ones.