First, I would probably try the tighten and loosen cycles on the bolt trying to get a little bit more turn each time. Maybe some more oil if I can get some down in the tab.

Second, if that didn't work I would hold the fin with a wrench and go to breaking the bolt off.

 

All kinds of things you can try. You could heat it (carefully) or freeze it with liquid niitro, smack it some with a punch, or find someone with an EDM machine.

I'd use PB Blaster for penetrant. :twocents:

 

Try working it between tight and loose while giving it some penetrating oil.

Can you get a heat source to it?

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Approaching this with caution as my concern is not hurting the lower unit housing.

You could put some heat to the trim tab anode but not the bolt as it’s in the lower unit housing.
I ran a small hose down to the bolt head and shot some penetrating oil down a couple times letting it sit for 48 hours. Nope

Appreciate the responses thus far

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Issue solved.

As mentioned I was able to loosen the bolt a bit so the trim tab was a little loose and provided a gap between the tab and the cavitation plate. I secured the tab up tight against the cavitation plate which meant the bolt in the housing stuck up a 1/8" or so in the casing. I then put two drinking straws together to form a tube that was 16" long. I dropped the tube down into the casing and placed it on the head of the bolt. I shot a significant shot of penetrating oil down the tube and worked the tube/straw around the flange of the bolt to get as close to the threads as possible.
Let it sit over night and went out this afternoon and it broke loose fairly easily.

Appreciate those that responded.

Pearl

 

Always nice when you don't have to break anything.

 

Put some Never Seize on it before you reassemble.

 

Tef gel works excellent for stainless bolts in aluminum. Prevents the corrosion from happening. I take mine apart annually to inspect and apply tuff gel.

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My Yamaha mechanic told me to never use "never seize" on outboard motors. It is a no no.


fop

 

Don't use anti seize on your outboard, or aluminum boat period. Using copper based anti seize will create big problems, you don't want copper in contact with any aluminum on your boat. Nickel based compounds are less reactive, and many so called "marine" anti seize options often contains zinc and/or graphite, neither of which are compatible with your outboard.

Tef-Gel or marine grease is a much better choice. I usually just use the Yamaha grease that's already in the grease gun sitting right there at maintenance time.

 

There are several types of Anti seize products and one is specifically for aluminum. I use it all the time (for many years) on all the screws and bolts on my Honda outboards and the spark plug threads on car engines with aluminum heads. Never had a problem.

I use the aluminum based from Loctite but I see there is a Marine Grade that has no metal in it that might be better....except there is a warning about severe eye and skin irritation with this one.

Another technique for loosening stuck bolts and screws is an impact driver. It is an inertia driver that you strike with a hammer to impart both shock and a slight twist to the bolt, nut or screw that is stuck. Prices from $15 to $60
https://www.northerntool.com/shop/t...utm_content=15825&gclid=EAIaIQobChMIkvO1y_Kr5wIVwRd9Ch0H2Q31EAQYBCABEgLPl_D_BwE

 

There are non metallic anti seize products which are safe, but the marketing schemes they use often aren't straight forward and easy for the consumer to understand. I recommended staying away from them for that reason, as there are safe and effective alternatives that boat owners likely already have on hand, when the anti seize in most garages will likely accelerate galvanic corrosion. Even Permatex "Aluminum" anti seize contains copper and graphite, which are not ok for your outboard.

Loctite has a few non metallic products as you mentioned, along with Jetlube 550, Star Brite has one, and a few others.

 

My boat mechanic advises me that once you break a bolt loose, take a coffee break. The breaking loose causes a lot of heat. Your coffee break Allis the bolt to cool down allowing it to be removed with a lesser risk of shearing.

 

As mentioned I was able to loosen the bolt a bit so the trim tab was a little loose and provided a gap between the tab and the cavitation plate. I secured the tab up tight against the cavitation plate which meant the bolt in the housing stuck up a 1/8" or so in the casing.

Good job. Sounds like the exposed threads allowed the oil to wick down into the threads via capillary action. :cheers: