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Old 12-20-2015, 02:29 PM   #1
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What Brand of Engine Mounts

I have been considering replacing all the engine mounts on the Hinos and generator, not because I know they're bad but because they're 28 years old. I know absolutely nothing about marine mounts so would appreciate some information on what to look for and what brands others have used and your experience with them good or bad. I plan on pulling the injectors and sending to a shop for testing and rebuild if needed, I want the engines running as smooth as possible. I've noticed at idle that I have things that rattle that never did before, I have 1615 hours on the mains and 1367 on the gen. Is there any advantage changing the mounts when their isn't a known problem? Thank you for your thoughts on this.


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Old 12-20-2015, 03:04 PM   #2
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Personally, if mounts are still within their serviceable limits I wouldnt change them.

The mounts on our 30,000 pound, twin-engine cabin cruiser were getting very tired when we bought the boat in 1998. The boat was then 25 years old. We were told by the engine surveyor that the mounts were nearing the end of their service life but they still had some time left on them before there would be metal to metal contact. This was confirmed by the friend we took with us to California to inspect, sea trial, and survey the boat. The friend until his recent retirement was the head of the engineering department at Alaska Diesel aka Northern Lights/Lugger. So he knows a wee bit about engine mounts.

Five years later an insurance surveyer noted that some of the mounts had reached the metal-to-metal stage. So we had all the mounts replaced.

This is a boat made in 1973 and it has all the vibrations machines this old and with this generation of diesels tend to develop. I have to say that the new mounts, which were very obviously putting a lot more rubber between the metal components of the mounts than the original, collapsed mounts, made not one iota of difference to the discernible vibrations of the boat.

So if you're thinking that new mounts will reduce the vibrations you feel when you run the boat, they might..... and they might not. Which is why I say replace engine mounts when the old ones have reached the ends of their service lives. Otherwise you may be changing something out that doesn't need changing yet for no discernible benefit.

There are different kinds of mounts that can noticeably reduce the vibration transmitted to an engine stringer. These are made with softer rubber. However, they can also affect the engine's alighnment. So switching to this type of mount may require a different kind of shaft coupler to be installed, one which allows the engine to move around a bit more without affecting the shaft alignment.

So make sure you get all the correct and accurate information you need from a truly credible source before making a change in the type of mount your boat was built with. That source, by the way, is not me.
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Old 12-20-2015, 03:55 PM   #3
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If it was my boat, I'd look at using these mounts:

Metalastik Cushyfloat Vibration Isolator | Parts | Trelleborg | Product Lines

With these couplers:

Marine Transmissions, Velvet Drive, Paragon, marine transmission parts, <marine transmissions>

Which is just what I did on my own boat, a 42' GB with 135 Lehmans. Made it super smooth running.

For the genset I'd stick with the OEM mounts but put the genset up on a platform that was held up by very soft Cushyfloat mounts.

Which again is what I did on my own boat.

Isoflex also makes very good mounts.

Isoflex - Marine Engine Mounts and Drive Couplings
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Old 12-20-2015, 03:58 PM   #4
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Natural Rubber Mounts have a theoretical performance lifespan of 20 years, in reality after about 10 years they are suspect to "performance" limitations. This means they no longer isolate vibration as intended, but still have plenty of life in them, they are just going to allow a little more vibration through to the structure. Waiting until they are metal on metal is waiting too long and by that time alignment will be impacted.

Generator mounts are easy, static load, no thrust, weight divided by 4 and pick a mount that will be loaded at approx. 70% of their maximum capacity and will provide whatever deflection you think you need.

Propulsion engines are a little more complex to choose the "best" mount solution. The weight of the engine, usually has a gear attached to the aft end which moves the CG aft, position of the mounts in relation to the CG, thrust from the shaft line and length of the shaft from the gear flange to the stuffing box or first bearing all need to be accounted for in selection.

There are easier methods, like a generic selection from a reputable company like Cushyfloat using simple guidelines. This is "wide spectrum" selection, is safe and easy, but will only be optimum by accident. These mounts are relatively inexpensive, a good value and good performers:

Cushyfloat Product Range - Trelleborg IAVS

It's time, and a good idea.

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Old 12-20-2015, 07:45 PM   #5
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Waiting until they are metal on metal is waiting too long and by that time alignment will be impacted.
Only if you assume the alignment will remain unchanged through the life of the mounts. It won't unless you have the kind of shaft couplers that compensate for changes in alignment as the mounts age. As we knew our mounts were wearing out we checked the alignment periodically to make sure it was correct. It did require a slight adjustment on occasion.
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Old 12-20-2015, 09:57 PM   #6
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I would have the alignment check. If they need replacing, they should be the same kind. Shaft alignment is important.
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Old 12-20-2015, 10:36 PM   #7
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Look at Poly Flex mounts.
I have them. Thought rubber mounts would act like a rubber ball and return the energy of engine movement. I concluded an engine mount should actually absorb energy ... not just reflect it.
Poly Flex mounts are not made of rubber. They are made of plastic or something very much like plastic that probably absorbs energy. And many people coment how smooth my engine is.

Phil,
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Old 12-21-2015, 01:16 AM   #8
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I would have the alignment check. If they need replacing, they should be the same kind. Shaft alignment is important.
The mounts most certainly do not have to be the same as original to achieve and maintain alignment

In fact many old mounts put on by boat builders were junk to begin with.
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Old 12-21-2015, 06:18 AM   #9
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Only if you assume the alignment will remain unchanged through the life of the mounts. It won't unless you have the kind of shaft couplers that compensate for changes in alignment as the mounts age. As we knew our mounts were wearing out we checked the alignment periodically to make sure it was correct. It did require a slight adjustment on occasion.
Alignment will not remain unchanged throughout the life of an engine mount. Mounts settle over time as you noted and the manufacturers provide parameters to measure for when replacement is recommended. An easy one is if all sides of the mount are the same difference from the base. The most common mount failure is the one under the injection pump from fuel contamination.

Shaft couplings do not compensate for misalignment. The cheap ones are "drivesavers" that protect the gear from wheel impact damage, and the really good ones reduce vibration going down the shaftline. Vulcan, Centa and Rubber Design make very good shaft couplings. Grand Banks used Rubber Design for many years standard.

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Old 12-21-2015, 07:03 AM   #10
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When repowering my boat, I did some looking around at different engine mounts, generator sound shield isolation mounts, and air conditioner isolation mounts. Ended up using Soundown for the isolation mounting and sound shield material. They have very good technical support for sizing of mounts and explaining realistic expectations based on what your doing. While I haven't gotten the boat in the water to run the engine and genset yet, the difference in noise level and vibration from isolation mounting the air conditioning units is amazing!

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Old 12-21-2015, 10:44 AM   #11
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Look at Poly Flex mounts.
I have them. Thought rubber mounts would act like a rubber ball and return the energy of engine movement. I concluded an engine mount should actually absorb energy ... not just reflect it.
Poly Flex mounts are not made of rubber. They are made of plastic or something very much like plastic that probably absorbs energy. And many people coment how smooth my engine is.

Phil,
Replacing most things on a boat is a golden opportunity to get something better.
True, but most times require something else to be changed modified. Had a water pump pulley replaced, which required a new water pump and motor mount modified. Anyway I try to replace with the same or closest to it. So what is wrong with metal on metal? The Eagles are sort of metal on metal with the metal spacers and metal motor mounts.
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Old 12-21-2015, 12:02 PM   #12
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Phil,
Very true. Many have purchased a new high tech anchor only to find themselves modifying their bow pulpit. Changing engines can bring about quite a few necessary changes. I got by easy. Very little was luck. It was just a good fit but usually it brings about more trouble than anticipated.

Re the Poly Flex mounts ... they were as easy to install as the original 30 year old rubber mounts the builder installed.
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Old 12-21-2015, 12:25 PM   #13
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So what is wrong with metal on metal?
There is nothing "wrong" with metal on metal. Commonly referred to as "hard mounted" many engines in both pleasure and commercial craft are installed rigidly, if that's what you refer to. Many may debate this but hard mounted engines are just not as quiet as resilient mounted engines.

On a resilient mount when there is metal on metal it means there is a failure of the isolation medium (Rubber, Plastic, etc) and now whatever isolation properties that were there are being short circuited by the metal on metal contact.

Note the attached. If the rubber elements in this mount fails and the top gold part is touching the black bottom part the engine in that location will move down vertically as much as 10-12 mm. This will "short circuit" any isolation properties and impact alignment.

What any good engine mount designed for marine use will do is provide "positive capture." That is if the isolation element fails the mount remains intact and the engine captive. Most marine engine mounts are considered durable driveline components and remain serviceable for 10-20 years.

All this refers to thrust taking installations, for thrust bearing installations like Aqua-Drive, Jet Drives, Outdrives, Remote gear drives, all of which are non-thrust installations, the rules are entirely different.

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Old 12-21-2015, 02:20 PM   #14
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Shaft couplings do not compensate for misalignment.
There are, in fact, shaft couplers that do this. They are used with very soft and flexible engine mount systems.
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Old 12-21-2015, 02:40 PM   #15
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I want to thank everyone who responded to my question with their experience renewing engine mounts. I have bookmarked all the links and will do some serious research after the holidays when I get back to the boat. My shaft alignment is in specs, I haven't checked my low idle rpm, it's possible that it needs adjusting but I doubt it. I know the SB drive plate rattles at idle and it's on the list to be replaced this spring, might as well do the port also as they both have the same amount of time. Also I appreciate the information on sound deadening material I have some on hatches that needs to be replaced.


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Old 12-21-2015, 04:22 PM   #16
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There are, in fact, shaft couplers that do this. They are used with very soft and flexible engine mount systems.
O K

I'm familiar with Centa, Vulkan and Rubber Design Couplings, not familiar with a brand that says you can have gross misalignment in the shaft line.

These brands will tolerate misalignment, will reduce vibration into the structure because of misalignment, will protect things like transmission seals and bearings from misalignment, but at the expense of significantly shorter service life. Basically they sacrifice themselves for bad alignment.

I am not familiar with any shaft coupling manufacturer that says its ok have a poorly aligned shaftline when using our coupling.


Why would anyone not want to align their shaftline?

What brand are you talking about?

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Old 12-21-2015, 04:31 PM   #17
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O K

I'm familiar with Centa, Vulkan and Rubber Design Couplings, not familiar with a brand that says you can have gross misalignment in the shaft line.




I'm not going to do your work for you. Do what you hopefully learned in school and research it. Here's a hint--- this brand of coupler system starts with the first letter of the alphabet.
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Old 12-21-2015, 04:33 PM   #18
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The Federal couplers will allow for some misalignment and even shaft whip.

But they still require you to start with proper alignment. And I'm sure they are not happy with any gross misalignment. Especially long term.
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Old 12-21-2015, 06:20 PM   #19
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I'm not going to do your work for you. Do what you hopefully learned in school and research it. Here's a hint--- this brand of coupler system starts with the first letter of the alphabet.
From an engineering perspective misalignment will create a loss of efficiency, and some component somewhere is going to have to absorb the energy loss. Could be a coupling, a gear seal, an intermediate bearing, a cutlass bearing, etc. but something will have to absorb the energy of misalignment.

As I said, shaft couplings will tolerate misalignment, they don't like it and it will shorten their service life. It's poor engineering and maintenance to not align your shaftline.

I don't need to go back to school to learn that.

Thanks for the advice though,

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Old 12-21-2015, 06:52 PM   #20
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I agree with Keysdisease on this one...

Any significant mis-alignment is wasted energy lost in the coupler that tries to correct it. Far better to put some effort into better alignment of the engine / transmission to the prop shaft. If you have a drive saver, after a long run, check the temperature of the drive saver and that heat buildup is lost energy in the drivetrain.

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