Engine Mounts

[mwert72655]

Has anyone had problems with engnine mounts in the 53 my or with any other hatteras yachts of this vintage (mine is a 1974), and what is involved if they need to be replaced? Thanks.

 

[Full Moon]

A couple of years ago I found that all my rear mounts were terribly deteriorated. I got a couple of bids to replace them and just the labor was $3000 to $4000. They wanted to clear out the salon and put braces over each engine hatch to lift the engines.

My old family mechanic looked at them and brought a little 2 ton bottle jack from his car and worked it like a three legged dog. Since they were attached at the front and the other side at the rear they didn't move much at all. The bottle jack was placed under the removed mount to support it while we cleaned the support and prepped the new mount to go back in. Taking our time it took about 6 hours to replace all four rear mounts and he charged me $240.00. You can't beat experience and common sense.

The worst part was finding the mounts. I looked at having them made, but once Steve at Sam's found the real ones I saw that making good replacements wasn't a good option. The worst part was the cost. 16 mounts times $120 each = $1920.00 and $240 labor.

Of course the best part of this story is the labor cost but I was extremely grateful to Steve for all his research to find these parts.

 

[Boatsb]

16 mounts? I have a 41C and there are 2 rear mounts per engine. Did I miss something? What engines and transmissions do you have?

 

[Brian Degulis]

I just finished replacing 12 mounts on a pair of 12 71s. The old mounts had not failed I replaced them with diffrent mounts for better vibration isolation. I split the shaft coupling raised the engine about an inch with a porta power Then removed the brackets from the engine slid the old bracket and mount out and the new in. I did the front first then the back I didn't have to disconect anything except the coupling.

Brian

 

[Fanfare]

My original 8-71N mounts consisted of the two metal ends with one or two sandwiches of black rubber apparently glued in between as there was no thru-bolting. This hard rubber gave some vibration damping between engine and hull. The weight of the engine and transmission eventually caused the rubber to sag, taking the engine out of alignment with the shaft. This must be corrected or the transmission bearings will fail. Unfortunately I can not remember how long it was until they sagged. Guessing 10-15 years. I replaced with the same DD mounts which I do remember were $$$! It was a bad design and will fail. Now I have mounts with thru-bolts and large rubber donuts on each side. Still good after about 15 years. They look as though the rubber donuts could be replaced without having to scrap the entire mount. I hope I'll never have to find out.

 

[Full Moon]

16 mounts? I have a 41C and there are 2 rear mounts per engine. Did I miss something? What engines and transmissions do you have?

Yeah you're right. Can't count. These are Twin Disk with 8V53s and there are one mount each side with two thru bolt mounts with doughnuts with metal plates attached on each side. 4 per side.

 

[mwert72655]

Wouldn't I notice the engine vibrate at different rpm's if the mounts were causing enough of an alignment issue to cause the transmission any stress???

It would seem to me that all the big diesel engines of this vintage would share the same problem, so should they all the mounts be replaced, or wait until vibrations develop?

 

[Brian Degulis]

What mounts do you have? Why do you think there is a problem? Post a photo of the problem? Lots of knowledge on this forum but you need to be clear about the problem.

Brian

 

[mwert72655]

I'm being told by a 3rd party that the mounts have deteriorated and may be hurting the transmissions due to alignment, but they don't vibrate at all so the question is, since there must be tens of thousands of these out there, what is the criteria for replacing them? If it ain't broke don't fix it doesn't necessarily make sense if there's "silent damage" being done to the thousands of transmissions out there connected to these engines...

So the question is: Can engines that don't vibrate do harm to their transmissions???

 

[sgharford]

Pascal has a great article pertaining to engine mounts and alignment at http://www.yachtsurvey.com/alignment.htm . I was going to ask the same question "how do you know when your mounts are shot" and then remembered reading this last year.

 

[yachtsmanbill]

I'm being told by a 3rd party that the mounts have deteriorated and may be hurting the transmissions due to alignment, but they don't vibrate at all so the question is, since there must be tens of thousands of these out there, what is the criteria for replacing them? If it ain't broke don't fix it doesn't necessarily make sense if there's "silent damage" being done to the thousands of transmissions out there connected to these engines...

So the question is: Can engines that don't vibrate do harm to their transmissions???

Only when you put 2000 lbs of weight in shear on a bearing! Alignment killed my Allison bearings, but whats 1/2" of mis-alignment between friends!
I still dont get why the 8-71s had those rubber mounts (??) Theyve produced nothing but horror stories over the years. The 12s have a great solid steel set up and I'll be danged if you can feel anything when running the boat. Even if I did, it makes it easy to get a feel for what going on downstairs... that is, if your in tune with your boat!
Of course, they probably didnt want to annoy the owner and his martinis while he was wearing his little captains outfit. Those days are gone! ws

 

[drburke]

..didnt want to annoy the owner and his martinis while he was wearing his little captains outfit. Those days are gone!

Yeah, I got rid of the outfit...kept the martini.

DAN

 

[krush]

I still dont get why the 8-71s had those rubber mounts (??) Theyve produced nothing but horror stories over the years. The 12s have a great solid steel set up and I'll be danged if you can feel anything when running the boat.

If I had to make a guess out of the blue, it would be because the 12v is naturally smother running than the v8 due to harmonics and stuff.

 

[sgharford]

I remember that from the dynamics class - a V-12 with 60 degree opposed cylinder banks is perfectly balalnced and did not require a harmonic balancer (in theory anyway).

 

[Brian Degulis]

Only when you put 2000 lbs of weight in shear on a bearing! Alignment killed my Allison bearings, but whats 1/2" of mis-alignment between friends!
I still dont get why the 8-71s had those rubber mounts (??) Theyve produced nothing but horror stories over the years. The 12s have a great solid steel set up and I'll be danged if you can feel anything when running the boat. Even if I did, it makes it easy to get a feel for what going on downstairs... that is, if your in tune with your boat!
Of course, they probably didnt want to annoy the owner and his martinis while he was wearing his little captains outfit. Those days are gone! ws

That set up's got nothing to do with 8 or 12 it's just a really crapy way to mount an engine. All boats should have some form of isolation mounts. Allowing the engines vibs to transfer thru the boat in the interest of rigidity and fool proof strengh is just flawed. Pushing vibration thru the structure over time will cause the exact problems your trying to avoid. Engine instalation 101.

Brian

 

[Trojan]

Before you change anything. Split the coupling and check the alignment. Then go from there. Even if there is some compression of the rubber over years. So what. Unless the rubber is deteriating there is no reason to change them. Like said, there for vibration isolation and should be on all engines.

BILL