Duty Cycle for rubber Engine Mounts ?

[Stretch]

I am concern about vibration from my 3gm30f. Should I have the engine mounts replaced, they look like the 20 yr old originals? How long can you depend on those rubbers to last. The mounts are not broken. Have you replaced your mounts to improve vibration ? The mechanic left a cryptic note on his handwritten copy that just said vibration. Perhaps that was caused with problems with the old exhaust valve that restricterd rpm to 2200 but I am just guessing.
There is one lower rpm the engine really shakes, but do all engines have that sour spot as well as a sweet spot for rpm ?
Donalex I am thinking would say replace...

Replace ?? or don't worry so much...

Thanks for your help[again]

 

[WayneH]

I had mine replaced earlier this year and it made a huge difference in the engine vibration. We had that sour spot you are talking about and it went away with the new mounts.

Take a close look at the rubber part of the mount. If it's chalky looking and cracked, I'd replace them. Although if they look like 20 year old originals then they are most likely shot and should be replaced anyway.

 

[petersea]

Replace them especially as they are most likely original and twenty years you have gotten your money's s worth, especially if you plan on keeping the boat any length of time. Yes new mount will help with a vibration but if it is a shaft or prop that is out of true it will still vibrate. Make sure to get the correct size and spec because most 3 gm used two different rated mounts (front and rear)

 

[Stretch]

Gotcha, 2 different mounts. I will add them to my order .

I am also going to put the draincock in the oil pan, like ''Nice n Easy'' has done. I have room under my engine to drain 2.7 L into a 4L plastic jug with one side cut open. Much better to get all the guck out with the oil that way.
Thanks for your posts.

 

[FastOlson]

Replace them especially as they are most likely original and twenty years you have gotten your money's s worth, especially if you plan on keeping the boat any length of time. Yes new mount will help with a vibration but if it is a shaft or prop that is out of true it will still vibrate. Make sure to get the correct size and spec because most 3 gm used two different rated mounts (front and rear)

All so true.
Any time after about 15 years they need to be replaced. The rubber steadily deteriorates and will also lose adhesion with the metal part of the mount.

L