At What Point Should One Become Concerned About Engine Mounts -- & Any Preventive Actions?

[rardiH36]

Yesterday, when I was getting up close and personal with my engine while replacing all the raw water and coolant circuit hoses, I took a close-up look at my engine mounts. (1980 Boat, owned for three years, Yanmar 2QM20.)

I noticed some rubber scrapings/dust in the interface between the metal "cup" part of the mount and the rubber "plug". In the picture attached, some can be seen on the left rear (-- I had already reflexively rubbed away the rubber dust from the front side).

At this stage is this anything to be concerned about? The mounts seem to be keeping the engine "contained" quite well. And the engine still seems to be aligned well with the prop shaft.

Also is there any type of action I can take to slow down the degradation rate, such as spraying the area with a lubricant of some sort?

As usual thanks for all your experienced opinons.

 

[Sanfelice]

In past years Yanmar mounts had some problems because they were made too soft and broke down quickly. I'm not sure of the years. If yours are original, then I would be a bit wary of them if you motor long distances. My experience was that the engine will idle fine with worn mounts since they absorb vibrations. If you look at the engine in neutral and it is rocking back and forth , other than mild engine vibes, the mounts are worn. If you accelerate quickly, and there is a lot of vibration and shuttering, the mounts may be worn. If you accelerate in neutral the engine may sound smooth but the real test is under stress.

By the way Yanmar mounts are very expensive but eventhough aftermarket mounts are cheaper they will not dampen vibes as much. Your picture does not look like later Yanmar mounts so they may not be stock. The following link may be of use to you.
http://www.yachtsurvey.com/Alignment2.htm

 

[jibes138]

To check your alignment you need to remove the coupling from the transmission, otherwise it will always show as aligned. What you really need to do is align your transmission output shaft with your cutlass bearing. If the engine is out of alignment the shaft might be perfectly on center of the engine from when it was originally tightened up but you could be side loading the cutlass bearing severely.

 

[sailaway78]

Take a very close look

While doing some other work, I found that a mount had sagged, and allowed the prop shaft to make contact with the bottom of the shaft log. The shaft log was tissue paper thin on the bottom. I was very close to having an encounter with a situation I don't even want to think about.

 

[rardiH36]

Sanfelice and Jibes138:

Thanks for your responses. The link to the yachtsurvey.com page was particularly interesting. Discouraging that the style of rubber mounting that I have is not recommended.

I just very recently had my boat out of the water. An inspection of the cutlass bearing by the yard manager revealed it was in good condition. No abnormal wear. When the engine is in gear and running, I can look down at the propeller shaft as it enters into the boat from the stuffing box towards the coupling with the engine transmission coupling. It's perfectly smooth with no off axis gyrations. Also in neutral, I can turn the shaft by hand with not a hint of binding. So the alignment I think is OK.

Yes the engine does vibrate and rock. But everything I have read about the 2QM20 is that this is just its normal quirky state. I'm mainly wondering about the small amount of rubber scarf that is being generated. Normal? Or Not?

Not too many responses to my question. Guess that engine mounts don't usually get anybody's attention ... i.e. they aren't a normal failure item.

 

[FastOlson]

It's just years and hours...

Actually, I would guess that mounts are a very normal failure item, but the old adage "out of sight out of mind" applies.


Here is a thread from when I replaced ours.
http://www.ericsonyachts.org/infoexchange/showthread.php?t=3997&referrerid=28
I went by the advice from an experienced diesel mechanic to replace them due to: 1) hours, and 2) years.
For our '88 model with upwards of 1500+ hours we were overdue.

As you will note from my summation, we had, totally invisible to the eye, collapsed rear mounts. i.e. metal on metal.

The rubber "elastomer" just breaks down over the years.

As long as the engine does not make an escape attempt and leap forward into the cabin, most sailors just keep this on their Ignore List.

As to whether to source some new ones from the engine vendor or go with another brand like we did, you're on your own! I suspect that there is some subjective evaluation to the whole vibration "cause and effect" narrative.

In our case, it wasn't until last summer that I finally had a really good alignment done and got it down to half a thou. That really smoothed out the engine, too.

Regards,
L

 

[rardiH36]

Re: It's just years and hours...

FastOlson:

I sometimes wish I were the type to put things into an ignore list ... but usually once something grabs my attention, it eventually gets done.

From the Erickson forum thread you referenced, this one was pretty good!:

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I asked my local repair dude about replacing my 18 year old 25XP mounts. He said, "that's a three cylinder isn't it?" I said, "Yes..." He said, "...waste of money. Those 3 bangers are gonna shake and rattle a bunch with new or old mounts. Save your money."

Maybe he just didn't feel much like changing them out for me...

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