Uh-Oh - What to do about this?

When I bought my boat and motor one of the clamp screws (correct terminology?) was seized. I figured "no big deal", I'll just use some penetrating oil and/or heat and get it loosened up. Well, I think the screw had already been fractured because after putting some heat to the boss and turning on it, it broke right off, never even started to turn. It is very stuck!

I did some searching on here for ideas on how to deal with this but didn't find much. Maybe I was using the wrong search terms? Anyway, any ideas on how to deal with this? The motor is a '67 9.5 hp Johnson.

If you're familiar with "easy outs" or bolt extractors you could give that a try. Basically you will be drilling into the remaining piece of bolt (size of hole determined by size of bolt extractor) and the extractor is basically a reverse thread that tightens in the direction you need to turn the bolt to get it out. My dad swore by brake fluid as a way to get stuck bolts unstuck. He once worked at a car wash and was also a farmer - both opportunities to have things rust up. I assume in your case the mounting and bolt are both aluminum - maybe a different problem. If you could get the motor off the stand you might try to twist off the pad at the other end of the bolt and get a vice grip on it. One possible way to break the grip of the corrosion is to apply heat to the area around the broken bolt. As the metals are the same they'll probably expand at the same rate but just the movement of the expansion may help to break the bond. Gook luck.

I would not have taken a torch to the aluminum bracket to break the clamp loose. Aluminum acts differently than a steel when heated. I am surprised the bolt broke before the bracket though. I would try to drill the old clamp screw out by drilling as close to center as possible. Drill as large a hole in it as possible without damaging the threads on the bracket itself. You want to be able to dig the remains of the bolt out of the bracket. It will be easier if they are as thin as possible. Then chase the threads with a tap to clean them up. If for some reason the threads on bracket do get damaged beyond repair you can insert a Heli-Coil insert in it if you have enough material left on the bracket to still give it enough strength for the job.

The bolts always break first. They are made for that. I bought several "kits" in my days for my OMC's.

Just make a nice clean starting point.
Center punch, and drill a small hole.
Bigger and bigger drills till your nearly to the Threads.
Then come up with something you can drive into that soft aluminum as an easy out.
I ground down a File, inserted it and unscrewed the old stuff right out of there.

Dont drive anything into those threads that will expand the threads enough to break the bracket.

There's no problem with heating that part.I would heat & let cool a number of times & it will thread out.I work with this stuff all the time.Used right ya can't beat heat.Be very careful when you drill your hole for the easy out, that it's centered.
When heating, let cool completely before heating again.The expanding & contracting will break it free.

Absolutely no reason not to heat that bracket!! Around salt water we call Oxy/Acetlyene the "blue-nosed wrench" as it is used almost daily for that exact purpose. Those of you in fresh water only areas count yourself lucky!. The way I see it is that you still have the other half of the clamp screw to grab onto and use to break it loose after heated. You have to use alot of heat, usually to the point of burning off the paint in the area. Repeated applications of heat and penetrating oil may help but I would definitely use the other end sticking out before drilling and tapping.