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Discussion Starter · #1 ·
okay i read a thread somewhere about someone replacing their motor mounts, they did not use yanmar mounts. on the replacements they used the studs where too short, so they used rubber vibration sheet to bump up the height a little. Raw Materials > Rubber > Sheets and Strips > Rubber,Buna-N,1/2 In Thick,2 x 36 In : Grainger Industrial Supply

so i thought why not replace the rubber in the mount with it. a few problems but not many mostly it is not going to be glued to the mount like the stock rubber. but hey we own things called bolts.

here is my idea, cut scrape what ever the old rubber out. then replace it with stacked layers of the rubber to the right height. now to hold it in place use a pin ( pictured in red below ) welded to the upper steel part, which fits in tight holes drilled in the rubber. these pins basicly align and center the rubber to the mount. then use bolts thru tightly drilled holes thru the rubber, with the hole thru the upper metal mount drilled larger to give room to viberate with touching the bolt. it would require stacks of rubber on top too with plates for the bolt heads to bear on.

what does every one think, it works out that all four mounts can be rebuilt for under 50 bucks vrs over a 100 per stock mount.

okay pics first a stock mount



now a paint drawing of my idea
black stock steel parts ( sort of )
gray rubber sheet
red alignment pins
orange bolts
blue backing plate

 

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Discussion Starter · #2 ·
now i know my drawing does not look just like the yanmar but you should get the idea, i drew it to be simple to look at and understand it
 

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$400.00

I was thinking more along the lines of the damage that might happen if they didn't work out. Just to haul my boat out for anything is close to $600.00.Not that it was a bad idea.
 

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ancient mariner
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yanmar engine mounts

the yanmar mounts are designed to cut down on vibration transmitted to the hull. when they design them they have to figure in the weight of the engine & transmission, also the thrust from the propellor. it would be hard for an individual to duplicate this, it is better to get the correct mounts.
 

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All too often, people tend to take the cheap route and find it to be a false economy resulting in an even greater expense later. Yo do it properly, the mounts have different specs depending on which side of the engine they are intended - how would anyone replicate that?
More important, the question arises - what difference does it make and what are the consequences of doing it wrong?
 

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mounts

Not worth it, get the factory mounts. Pretty cheap in the scheme of sailing things. Also the bolts will transmit vibrations from the motor to the engine bed. I have seen this tried before. There are always mounts on E-bay for cheap.
 

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the yanmar mounts are designed to cut down on vibration transmitted to the hull. when they design them they have to figure in the weight of the engine & transmission, also the thrust from the propellor. it would be hard for an individual to duplicate this, it is better to get the correct mounts.
Yep, I agree. The propellor is commonly believed to push the boat but in fact the propellor pushes the engine/gearbox which in turn pushes the boat.

The connection between the engine and the boat (the mountings) gets a whole lot more energy through it than is normally understood. If the mobility (or lack thereof) of the mounting is compromised, the whole drive line integrity goes with it and then you get vibrations (from both the bolt contact as well as the shaft misalignment), water leaks, stress cracks, etc.

No, I reckon the money you save by making up Heath-Robinson mountings will be burned away very quickly in additional maintenance. Get the real thing.
 

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The connection between the engine and the boat (the mountings) gets a whole lot more energy through it than is normally understood. If the mobility (or lack thereof) of the mounting is compromised, the whole drive line integrity goes with it and then you get vibrations (from both the bolt contact as well as the shaft misalignment), water leaks, stress cracks, etc.
I would agree that the integrity of the mounts is critical, however, this still doesn't answer my question - as long as someone, such as the OP, can make a mount which is structurally secure and which minimizes vibration, what difference does it make who constructs it?
This type of fabrication isn't "rocket science".
 

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Francophobe
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I would agree that the integrity of the mounts is critical, however, this still doesn't answer my question - as long as someone, such as the OP, can make a mount which is structurally secure and which minimizes vibration, what difference does it make who constructs it?
This type of fabrication isn't "rocket science".
Funny that we are sitting here in a cold winter day sort of like a day in 1986 when a rubber part on a rocket failed with catastrophic results. Unfortunately, getting vibration damping and force transmission correct on a system like this is a bit like rocket science. Yes, you can make up a rubber mount of your own. No, without many equations, prototypes, and modifications will you get it as good as the Yanmar mounts. They have spent years designing them and using force gauges to make sure it works right. Somewhere in the back of my mechanical engineering mind lies the training to do this work - but I wouldn't bother spending the many hours to attempt it.
Remember the lesson from Challenger - what works right on your drawing board may act differently when hot or cold or soaked in diesel or after 10 years in your engine compartment.
 

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You are right, it isn't rocket science. Or brain surgery.
That said. In the picture of the factory mount you may notice that there are no through bolts between the bottom and top plates. The reason is because you have an engineered rubber composite of very specific compound that is chemically bonded to the plates. There is no way you can replicate that bond in your garage, it does require special equipment. Also your idea of individual stacked layers of rubber will not come close to dealing with the torsional loads the mounts will see. As everyone has already said, it isn't about how much you will save but more about how much damage you will do to your boat. Do you really want to save a couple of hundred dollars and end up destroying the trans or engine or mounting bed or maybe all 3?
You are probably better off leaving the old worn mounts in place then trying to 'build' something that is poorly engineered. Some things just aren't worth short-cutting.
For the record, when I was young and broke and had a broken engine mount on my car, I tried many ways of getting around buying a new one, all of my attempts failed miserably and in the process managed to trash all the other mounts due to the increased loads on them.
My solution to save a few bucks cost me a bundle.
I am guessing your boat is probably worth a proper repair.
 

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You are right, it isn't rocket science. Or brain surgery.
That said. In the picture of the factory mount you may notice that there are no through bolts between the bottom and top plates.

Yes and sandwiching rubber strips, that are going to move, will eventually sheer the heads right off the bolts and the whole mount will fail. Also Murphy is always waiting for you so this will of course happen at the most inopportune time..;)

As others have said these mounts have a lot more science in them than cutting a couple of floor mats up and bolting them together.. Yanmar mounts are free floating with NO bolts penetrating the rubber let alone four or six of them. They are designed to move more in certain directions and less in others. The rubber mount is engineered and designed to allow the torque to be transferred appropriately and not cause damage to other components.

The phrase "penney wise & pound foolish" comes to mind on this forum quite a bit and this thread is no different..
 

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I have motor mounts for engines puting out over 3,000hp but the loads were in just one direction.

Because these mounts must take a thrust load and if it does not bad things will happen.

I vote for the factory ones for that reason.

ON SECOND THOUGHT----BUILD THEM.
YOUR DESIGN WILL WORK
IF YOU GET TO MUCH ENGINE SHAKES TO MUCH THEN YOU CAN SAVE UP FOR THE FACTORY ONES.

I would try to keep the installed hight the same for engine alignment.
 

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I have had a failure on one of my mounts, in the 1st month, but it was the stud that failed due to over torque on instrallation.

Don't forget that marine engines also have stress side when the boat is powered, and is sailing, higher heel angles.

also, Saildrive engines only have support in the front of the engine, the rear supports are repalced by the support provided by the saildrive.

Since this is a critical issue, I go with original stuff..The seal on the SD may get damaged, then no good complaining to the factory.
 

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Discussion Starter · #17 ·
i would definitely keeps the alignment issues the same. not trying to convince anyone, but my idea would have about a 1/4 in any direction except up before the bolts hit. i am also not saying it would work, but i know i need at least 1. i also need to do my shaft seal and i dont have the room to back off the nut ( labout a 1/4 inch to the plate on the shaft ) so i need to pull the engine. so while i pull it out i am going to do all four and realign everything. right now when i hell to starboard the engine really shakes
 

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what does every one think, it works out that all four mounts can be rebuilt for under 50 bucks vrs over a 100 per stock mount.
I'm all for diy stuff but for this bite the bullet and buy the real ones. What happens if all 4 give way when you need the power for whatever reason and gun it? Rotating heavy stuff scares me, especially close to fiberglass that keeps the water out.
 

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Scottyt's engine will be held in place with 16 bolts with his designed mounts.

Your engine is held in with glue.

Wich one would you want to have if your boat was rolled and all the weight of your engine and trans was hanging on them, rubber and glue or bolts?:rolleyes:

I'm all for diy stuff but for this bite the bullet and buy the real ones. What happens if all 4 give way when you need the power for whatever reason and gun it? Rotating heavy stuff scares me, especially close to fiberglass that keeps the water out.
 

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Scottyt
If you haven't sourced your rubber I would recommend going to a truck parts store and getting a truck mud flap.

Get one that has a couple of belts of material in them and you will avoid any stretch and will hold your pin and bolts in perfect location.

The flaps are made from conveyor belting and are very tuff.
 
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