Yanmar Engine Mount Worries

[jssailem]

I'll hazard a guess here.
The shop when deciding to install the motor moutns thought it would be a good idea to put the 100's on the side that the motor will compress when the engine is advanced. This address the downward forces from the torque of the engine.

The greatest torque when the engine is put in gear and the throttle is advanced happens where the engine and transmission are located. The mounts would receive two forces at the mount. Up on one side and down on the other. I suspect that is the reason Yanmar states that the mounts should be 100 near the transmission/engine and 75 at the other end of the engine is because they are addressing both of the forces generated.

 

[jdrutten]

As far as fore/aft vs. port/starboard differentiation in motor mounts: all I can say is that Hunter did mine with the 100's on the port side and the 75's on starboard. ...

Now I wonder how the mounts are installed on my h306. To my largely untrained eye, I feel like my engine vibrates more than I'd like, but I wouldn't say that the front vibrates any more than the rear. Then again, I never looked at 1200 rpm in neutral while sailing. But if we go by the manual and assume the front requires "100" mounts, it would seem like port/starboard mounts would affect one corner more than anywhere else and result in more of a diagonal bounce (one corner is stiffer, while the opposite corner is softer than spec), instead of the hobby-horse bounce you describe. Of course, it may not be particularly related to what you're seeing anyway. Unfortunately I won't be out again to see if my install is similar until Saturday.

... I suspect that is the reason Yanmar states that the mounts should be 100 near the transmission/engine and 75 at the other end of the engine is because they are addressing both of the forces generated.

As I read it, the 100 mounts are at the front by the alternator while the 75's are at the rear by the transmission. Someone more knowledgeable than me will have to confirm if a larger number relates directly to stiffness, or if it's like wiring and a smaller number relates to larger stiffness.

 

[jaysweet]

Now I wonder how the mounts are installed on my h306. To my largely untrained eye, I feel like my engine vibrates more than I'd like, but I wouldn't say that the front vibrates any more than the rear. Then again, I never looked at 1200 rpm in neutral while sailing. But if we go by the manual and assume the front requires "100" mounts, it would seem like port/starboard mounts would affect one corner more than anywhere else and result in more of a diagonal bounce (one corner is stiffer, while the opposite corner is softer than spec), instead of the hobby-horse bounce you describe. Of course, it may not be particularly related to what you're seeing anyway. Unfortunately I won't be out again to see if my install is similar until Saturday.


As I read it, the 100 mounts are at the front by the alternator while the 75's are at the rear by the transmission. Someone more knowledgeable than me will have to confirm if a larger number relates directly to stiffness, or if it's like wiring and a smaller number relates to larger stiffness.

Well, first of all, keep in mind that I've had these same mounts since 2004, so this hasn't been a problem in all that time. The main thing I've always been careful about is not to leave the engine at a slow idle (maybe 700-800? I'm not sure) for long, because it has always had a bad vibration at that speed. I always start in neutral and get it up to 1100-1200 as quickly as possible to warm up, since that's the smoothest near-idle speed.

As for what to check for, the numbers (75 or 100) are molded into the rubber. The two 75's were on the outside, so easy to see from the head (starboard) side. The two 100's were stamped facing the engine on the aft cabin (port) side, but I was able to take a picture with my iPhone with the flash turned "on", with a little trial and error. I'm not sure it would have been possible to get my face down there close enough:


The flakes aren't anything bad: apparently someone decided to hit everything (including the rubber) with a coat of black spray paint, which didn't last.

 

[dLj]

Don't you just love portable digital cameras? I've been able to take photos to figure stuff out that I'd never have been able to do as well without...

dj

 

[jdrutten]

...
The flakes aren't anything bad: apparently someone decided to hit everything (including the rubber) with a coat of black spray paint, which didn't last.

Mine has the same flaking paint. Sure, it looks terrible now, but I'm sure when it was fresh it probably looked "Pretty Dang Spiffy."

 

[jaysweet]

Don't you just love portable digital cameras? I've been able to take photos to figure stuff out that I'd never have been able to do as well without...

dj

So far, I've found them pretty useful. I haven't yet gotten one of those sigmoidoscopes (or whatever they call the non-medical thingys ), but i'd like to get one to check out my... fuel tank. Or whatever else needs examining. On the boat, of course.

 

[jaysweet]

Mine has the same flaking paint. Sure, it looks terrible now, but I'm sure when it was fresh it probably looked "Pretty Dang Spiffy."

Kind of wish they'd just powder coated the steel bits and left the rubber alone. But that's just me.

 

[jdrutten]

I’m afraid I don’t have much to add here. I was only able to persuade about 2 knots of boat speed with light winds and had to actually start the shaft spinning by hand. I can only report that at 2 knots there was no motion to my engine. I also got a look at my mounts and they seem to be third party mounts and they were all identical.

 

[jaysweet]

I’m afraid I don’t have much to add here. I was only able to persuade about 2 knots of boat speed with light winds and had to actually start the shaft spinning by hand. I can only report that at 2 knots there was no motion to my engine. I also got a look at my mounts and they seem to be third party mounts and they were all identical.
View attachment 209716

Sorry: meaning you got 2 knots under sail, and this caused no auto-rotation of the shaft as well as no engine vibration? Well, that's a good thing!

I'm not sure I'd conclude that those mounts are 3rd party. They might well be the same as mine. You've got the same black spray paint on the lower nut there that I had. What year is your boat?

 

[jdrutten]

Sorry: meaning you got 2 knots under sail, and this caused no auto-rotation of the shaft as well as no engine vibration? Well, that's a good thing!

I'm not sure I'd conclude that those mounts are 3rd party. They might well be the same as mine. You've got the same black spray paint on the lower nut there that I had. What year is your boat?

I've got a 2004. The reason I think they might be 3rd party is because they don't have what I assumed were standard markings for "75" or "100." Mine just say "02". But yes, still plenty of flaky paint to go around.

 

[Crusty Ol Salt]

I'm a follow the manual kind of guy. I never, ever assume that the "highly trained technicians" at the factory knew what they were doing when they did what they did.

My Dad told me never buy anything the built or repaired on a Monday or Friday. Monday no one wants to be there. Friday everyone wants to go home.