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DrB 01-12-2010 12:08 PM

Motor Mounts on Yanmar
Looking on advice on motor mount replacing. My Yanmar 3GM30 has rubber bushings in the motor mounts that help damping the vibration. Sorry no pict. I think that they are starting to go and would like to replace them. Can I easily do this? Do they sell the rubber bushing and how easy to swap? Any things to worry about when doing such as maintaining alignment?



arf145 01-12-2010 12:37 PM

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Oh yeah, you totally have to worry about alignment whenever you mess with the mounts.

What do you mean by "bushings"? The standard Yanmar mounts at least for the 2GM.... that I'm familiar with look like the one below that ScottyT posted here at Sailnet, a steel frame with the rubber bushing inside. You might have different ones for front vs. back with different stiffness--the 2GM does.

They aren't all that hard to swap out, though I had to lift the engine a bit with a jack, but you do have to disconnect the shaft and then realign when you're done.

Why do you think they are shot?

RonRelyea 01-12-2010 12:47 PM

Possible stupid question of the day ...
Can you carefully replace the engine mounts one at a time and get them in the same position as the old one ... and then not have to re-align the engine/shaft? I'm not familiar with how difficult a shaft alignment job is ... and I guess that's my second question ... how difficult is the alignment process?

A couple of my mounts are pretty rusted due to the PO ignoring a leaking raw water pump and I'm thinking of taking them out one at a time for clean-up / repainting and new bolts

arf145 01-12-2010 01:20 PM

Ron, I think you can only get close that way. The typical tolerance at the coupling is something like 0.006 inch. And even if you got them back in the exact same spot--and believe me, I tried this myself--you might find that time and deterioration has made the old spots less than perfect anyway.

If you've got a coupling directly to the engine outpu and no plastic drive saver doughnut inbetween, you mainly just need a small enough feeler gauge and some patience as you shove the engine around.

And if we're still talking Yanmar here, you definitely will need to disconnect the shaft, because the post on the mount is pretty high and the engine will need to be lifted up and over it. You don't want to be trying to do that while connected to the shaft.

RonRelyea 01-12-2010 01:49 PM

well ... like I said .... stooooopid idea!
yeah ... I've got a yanmar 3gm30 ... and a little thought about the post height would have supplied my own answer ...

I do have a drive saver too ... so ... I'll start a new post rather than hijack this one any further! Thanks ARF145

mitiempo 01-12-2010 03:32 PM

You can get close by adjusting the new mounts by moving the nuts to the same position as on the old mounts. But because the softness will be different between new and old mounts there will still be a difference, it will just be smaller. Mounts cannot be refurbished, only replaced and you're best to use the Yanmar mounts as opposed to aftermarket ones. Re-alignment isn't hard just fiddly to do and usually in a fairly tight space.

Gary M 01-12-2010 05:48 PM

I had my 2GM out this summer, would have been a great time to replace the mounts. How do you tell when they need to be replaced ? My engine seems to have a lot of movement, I assume that means the mounts have lost a lot of rigidity but is there a guideline on how much is too much?


mitiempo 01-12-2010 06:02 PM

It depends. Yanmar recommends every 2 or 3 years but I'd bet nobody does it that often. Yanmar mounts are quite soft. In my experience they harden with age as the rubber gets older. There are probable a lot of 20 year or older boats still with the original mounts.

roline 01-12-2010 07:17 PM

flex couplers
3 Attachment(s)
All elastomers have cross linking agents to initiate the curing of the base elastomer. The elastomers due continue to cross link due to aging. Exposure to temperature accelerates the aging process. When motor mounts are old, they usually will have taken a set in the loaded position, and then aged, become firmer, with reduced flexability. In the case of engine seals, the elastomer can become brittle and crumble/ break, leak... As motor mounts age, the shaft alignment should be checked due to the sagging and taking a set. Flex couplings can be used to minimize vibration of misalignment, but should not be used in place of proper alignment. The usually do not like more than 6 to 8 degrees of angular misalignment. Examples of polymer / elastomeric couplers:

arf145 01-12-2010 10:46 PM


Originally Posted by RonRelyea (Post 559130)
yeah ... I've got a yanmar 3gm30 ... and a little thought about the post height would have supplied my own answer ...

I do have a drive saver too ... so ... I'll start a new post rather than hijack this one any further! Thanks ARF145

It's not a total hijack, so I'll throw one more note out there--to align with a drive saver, you just need to remove the saver and pull the shaft in a bit so you can align metal to metal. When the alignment is good, reconnect with the saver in place.

I embarked on that little journey of discovery last summer while having someone "just" do this for me because I was afraid to mess with the shaft while in the water--visions of water gushing in. Removing the saver revealed a shaft that protruded past the end of the coupler into the saver center, preventing mating them up. Had them saw that off on somewhat of a deadline for a trip, but that revealed that the coupling was warped and couldn't be aligned anyway. We put it back together and got a rough alignment that got us through the season. But I'm having shaft, coupling, and cutlass bearing replaced, and while we're at it, a nice PYI seal done this winter. $$ but hopefully :) :)

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