Reply To: stuck lower unit bolts ’78 Erude 4hp long shaft

[Don]

Well, I wouldn’t actually run the engine on a boat with just one bolt attached, except at slow speeds.
You mention the hex head of the remaining bolt is rounded off, so you may just want to drill into what is left of the hex head so it falls off. Trying to use heat at this point won’t be real effective because you can’t really get the heat near where the corrosion is, and you may end up melting the aluminum extension/gearcase.
Once the hex head is drilled off, try prying down to see if the gearcase will come off…The gearcase may come off leaving the extension still stuck, but maybe now you can get the heat inside where it is needed to work the extension down and off, I’m guessing there is plenty of salt/rust holding the bolt shank to the extension housing. Once the extension is down an inch or so, perhaps it is best to cut the bolt shank off between the extension and exhaust housing leaving plenty of the shank exposed, so you can work on that later with heat and vice grips.
Be very careful and patient, excessive heating will melt the thin extension housing and gearcase castings…
Let me know if you have questions about what I have prescribed, I realize that a decent picture would be worth much more than my words…