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Old 22-03-2019, 16:55   #1
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Completely seized nut on engine mount

Unfortunately the PO let the heat exchanger drip seawater on the starboard engine mount for years. I can feel the washer below has some wiggle room and the engine vibrates more than I believe it should. So it's due for an alignment.

But first I need to get the nut off.

I don't own a torch or have any real way to apply intense heat, and I'm hesitant to use PB blaster as I believe it will damage the rubber in the mount? Would a nut splitter like this have some success? Unfortunately I already paid a mechanic to fix this last season and he couldn't get it to budge (and left me with the $500 bill). Really trying to minimize any further cost here, but I understand engine alignment is very important.

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Old 22-03-2019, 17:07   #2
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Re: Completely seized nut on engine mount

Matt - I am no expert, but I had a similar challenge when I replaced the motor mounts on my Yanmar last spring. Try soaking the nut with PB Blaster, but put an oil diaper on top of the mount to minimize the amount of blaster that gets on it. Let it soak overnight, tap it occasionally with a hammer, and see if it will back off.
If not, find a torch and heat it up. I doubt you’ll be able to get a nut splitter on it.
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Old 22-03-2019, 17:09   #3
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Re: Completely seized nut on engine mount

The nut splitter would be a good possibility. It might work more easily if you get a Dremel with a cutoff wheel to start the cut.

BUT if this is the original 1984 motor mount maybe it's time to replace it. New mounts aren't that much and you could just cut off the old one and not have to fight with it.
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Old 22-03-2019, 17:11   #4
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Re: Completely seized nut on engine mount

The best penetrant is a 50-50 mixture of acetone and automatic transmission fluid that you can make yourself. Apply using a dropper or syringe and leave alone for a couple of hours or overnight. Then see if the nut breaks free. This has worked for me in cars. I’ve heard that if it doesn’t loosen easily, tighten it slightly and then loosen. You can read more about the penetrant here:
https://www.bobistheoilguy.com/forum.../Acetone_antis

If this doesn’t work, use a hacksaw (manual or electric)

Good luck and let us know how it goes
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Old 22-03-2019, 17:12   #5
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Re: Completely seized nut on engine mount

Matt, seriously rusted steel bolts can often be released using

Reducteur 300g Super Rust Release Agent

this isn't a penetrating oil but something that chemically attacks the rust and breaks it down. I've had good luck with it on just the same problem you are addressing.

Commonly available here in Oz, likely so in the USA.

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Old 22-03-2019, 17:25   #6
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Re: Completely seized nut on engine mount

Have you got a replacement mount ? However you get the nut off, you won't be able to just thread a new one on.
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Old 22-03-2019, 17:36   #7
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Re: Completely seized nut on engine mount

Quote:
Originally Posted by Calif.Ted View Post
Have you got a replacement mount ? However you get the nut off, you won't be able to just thread a new one on.
No, I haven't ordered a new mount as of yet. I guess I was optimistic that the threads might be saved.

Someone else asked if I plan to just replace the whole mount and I am hesitant to do that because my engine is completely enclosed under the cockpit floor, so I'm not really sure what technique I would use to lift it up and swap the mounts. Any ideas most welcome.
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Old 22-03-2019, 17:44   #8
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Re: Completely seized nut on engine mount

Yes!! A nut splitter,(as you have shown) is one of the most non-destructive ways to split a nut enough to allow its removal without damaging WHAT IS LEFT of the threads-or any near components.
It is a cheap & (IMHO) a necessary tool if you plan to do any maintenance on your boat.

If this method is successful,you can clean up the existing threads with a steel wire brush,followed by a "thread die" or "nut runner" of the appropriate existing thread & pitch.
Then -use a NEW nut of proper thread & pitch.






If you need to adjust the height of this mount,you will probably have to repeat the above procedure on the nut just under the motor bracket-the elevating nut.Replace this with a new nut-- if required.


Use of a REASONABLE amount of your favorite rust penetrating fluid should not affect most modern motor mount "rubber".(Cover the rubber with rag/plastic if you like).


NOTE: Motor mount nuts are often 1/2 the thickness of a "normal" nut of the same size. This is to allow for two "thin" nuts to be installed,one behind the other,and then "locked" together by rotating one CCW & the other CW,against each other.
This method works way better than any "lock washer,etc." method,when dealing with vibrating equipment.


Properly called a "Jam Nut" https://www.google.com/search?client...q=hex+jam+nuts




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Old 22-03-2019, 17:45   #9
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Re: Completely seized nut on engine mount

I had the same issue with a 30 yr old mount. That’s why I own a sawzall. Which has been surprisingly useful. Cut it up and replace it.
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Old 22-03-2019, 18:49   #10
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Re: Completely seized nut on engine mount

Hello, Matt,

Really, try the Reducteur. It is amazing how well it works. No affiliation. If you other guys haven't tried it, you might consider it if you have something rusted up. We also have used the "weasel piss", equal parts ATF and acetone, for a penetrating oil, with success. But for chemically altering and breaking down rust, the Reducteur is the ticket.

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Old 22-03-2019, 19:22   #11
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Re: Completely seized nut on engine mount

First thing you have to do is get off as much of the rust scale as you can. Us a wire brush and clean it up. toothbrush and some oil maybe to get in the tight spots. Then you can use whatever penetrating liquid you choose. Sometimes you can get a frozen nut to start moving using a cold chisel and some light taps with a hammer.
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Old 22-03-2019, 19:24   #12
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Re: Completely seized nut on engine mount

In a hardware store that sells metal gutters, they should have the acid used on galvanized sheetmetal before soldering. It comes in a gallon, but usually they have a small bottle, too.
The acid will eat the rust down to good metal and should also flow down the threads, probably leaving the nut loose. It may take a couple applications to clear the threads as the acid looses power as it eats rust. It is neutralized with baking soda and water.
The nut splitter probably won't fit in the space.
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Old 22-03-2019, 19:40   #13
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Re: Completely seized nut on engine mount

Looks like a Bushing Inc mount. You might consider just replacing it with the exact same one. Theyre good but the bottom of them are notorious for spinning. They're cheap, only about $41 each if you order direct. It's not that hard to do with a car jack ,crowbar, and couple blocks of wood.

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Phone # 248-650-0603
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Old 22-03-2019, 21:59   #14
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Re: Completely seized nut on engine mount

Most of the ideas above are good, but the nut splitter won't work unless you modify the engine bracket.

If the mounts are 45 years old, and you can afford it, replacement is probably the best idea, but, properly, they should be replaced as a set.

Usually the engine bracket is bolted onto the engine, if so, it will probably be easier to remove the bracket and mount as an assembly and separate them on the bench.

Neither the top nut on the mount stud or the bolt through the plate into the mount bracket appear to be tight, as the lock washers on both are not compressed.

After knocking the rust off and putting some penetrating oil on, you may find that it turns fairly easily. If not, an undersize box end wrench or six point socket may be driven on to enable you remove the rusted nut.

But that still leaves you with cleaning the stud's remaining threads...


When you get it off, whether you replace or reuse, when you reassemble, liberal application of neversieze is highly recommended...
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Old 22-03-2019, 22:33   #15
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Re: Completely seized nut on engine mount

You could also saw the nut apart with a sabersaw. Just outside the threads. Have done it, works, but easy to damage the threads. I agree, it is probably time to change the mounts. These are not expensive if you buy them from the right place, i.e. not from the engine manufacturer.
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