Completely seized nut on engine mount

[boden36]

You could drill three small holes into the nut (centre punch first), but not into the stud. Mark the drill with a bit of masking tape to set the depth. Then use a slightly larger drill so the holes just meet. Finally, expand the nut with a good sharp cold chisel.


Regards,
Richard.

[RaymondR]

If you can get an electric drill in there and drill a small hole parallel with the bolt axis through the nut on opposite sides then open the holes with bigger drills you will be able to split the nut with a cold chisel.

[ptards]

Brace the motor somehow (blocks of wood, etc) and remove and replace the mount, its aged and a good chance its the reason for the vibration.

[MartinR]

Originally Posted by RaymondR

If you can get an electric drill in there and drill a small hole parallel with the bolt axis through the nut on opposite sides then open the holes with bigger drills you will be able to split the nut with a cold chisel.

I will remember this for next time. This is a good idea.

[Suijin]

I would replace the mount and as many of the others as you can. The rubber is most likely already shot. I replaced my four mounts, original from 1986, last year and the increased smoothness was dramatic. One of my mounts looked like that.

A car jack and some scraps of wood to lift the engine. Cut the bolt and remove and replace the mounts. One less critical system to then worry about.

And vibration is bad. It can lead to premature wear in a number of areas.

[phorvati]

You might not need to support the mount. If you have other three, then engine won't move. Just don't beat on it with the sledge hammer. I keep and use cordless angle grinder for stuff like this. I also have map gas torch. You have to be carefull with either. Below is my engine mout. It was broken all along. 5/8" stud was there before, and my engine and tranny weigh 1200lbs. 5/8" stud was too small. I think 5/8" is for much lighter engines like 450lbs or so. So I used the opportunity to get a 3/4" stud. That required adapting the engine bracket. Moral of the story...don't skimp out on this. Double check the numbers and do it right. Few months later I did my other rear mount. I still have the smaller forward mounts and I'll have to get to them soon.

[Boatyarddog]

Originally Posted by matthidinger

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.

https://www.amazon.com/Teng-Tools-Pi...gateway&sr=8-6

I've had amazing success with a product called Kroil, a bit pricey but works really well, just let it soak in.
Heat will destroy the bushing for sure.
Seems once you get that nut off you'll be let with how to get it out of the mount.
You might consider drilling a small 1/8 to 1/4" hole in the side of the mount and spray Kriol in there too.
You can use PB too just don't soak the rubber with it.
Good luck,
Cheers
SV Cloud Duster

[DaveSIM]

[QUOTE=bigdogandy;2853796]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.[/
QUOTE] you can use a hair dryer or a heat gun to heat up the nut before undoing it. A long bar with a socket if you can get it in there will do the trick. All else fails use a dremel tool with a metal cutting blade and cut the nut in half. Don’t worry about the cutting the mount bolt, as you should replace the mount anyway. You can get them for around $30 a mount. A torch might be better but I would make sure you don’t start a fire. Davesim

[Boatyarddog]

Originally Posted by skipmac

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.

On second look you might just cut it out and replace it, that's gonna be easier.
Support the engine and remove the mounting bracket to release the mount, as well remove the stringer bolts.
Cheers
SV Cloud Duster

[Scubaseas]

All good ideas but my $.02 as a professional mechanic of 50+ years would be to buy new motor mounts. Even if you get the nut off it looks like you do not have enough thread left to properly adjust the engine. Why spend hours to try and save a motor mount that should be replaced anyway?

[Chuck Hawley]

Originally Posted by skipmac

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.

Excellent point. They don't last forever. My four Yanmar mounts looked good, but the engine bounced around quite a bit. It turned out that three of the four had "tears" in the rubber blocks and had failed. Hard to determine with the engine's weight resting on them.

Chuck

[Shoalcove]

I’m with the cut it off and replace it camp. Although, I’d be tempted to take a hard look at the other side and maybe change the pair if I thought they were nearing end of effectiveness. It sounds like you are going to have to realign the engine anyway.

[Wulf]

This shouldn’t be difficult if you have access.
1. Clean Off the exposed stud & nut.
2. Apply penetrating oil of your choice.
3. Using a hammer & fairly large, sharp chisel hit the nut on the flat; chisel aligned with the stud.
This effectively spreads (expands) the nut slightly on the threads facilitating removal. You typically won’t need to cut right trough the nut unless it’s really stubborn.
Done this many times over the years with great success and without any special tools.

[George DuBose]

30+ year old motor mounts? I would change all of them, changing just one sounds like something will be out of balance. Use a small scissor jack to lift the engine and change the mounts one at a time. Then align the engine/propshaft.

[mattman]

Thanks for the tips everyone. I'm going to go ahead and just replace both rear mounts. I don't think they are quite 30 years old, but they are at least 10. Should I also replace the forward mounts? They seem to be in OK condition from my visual inspection, but of course hard to say.

These appear to be the rear mounts:

https://shop.toadmarinesupply.com/sh...=mdd&x=14&y=16

This is probably the most "challenging" engine work I've undertaken so far. I am buying a small scissor jack and taking some scrap blocks of wood and hoping I can position the jack under the engine. Someone mentioned I could just rely on the other 3 mounts to hold it in place while I swap one out at a time. Have others had success with this?

Any other general tips on replacing motor mounts and alignment? I know I need to remove the 4 transmission coupling bolts before I try lifting anything, and will be purchasing a digital caliper to measure the height of each existing mount. I'm a little lost on where the use the feeler gauges to adjust the engine alignment though.