Re: How do I prep lower unit bolts for removal?
Most of the problems will be with the pump housing bolts and the hidden bolt inside the exhaust snout. The six external bolts usuallu come out all right. If you should strip them, they can be re-tapped to 3/8 inch and you can cut down some bolts to length. You will need to drill the case a hair over 3/8 though. Propane will not melt aluminum. Heat and cool several times to shock corrosion. Also steady pressure will exceed the bolt strength and twist them off. Use a hand imact wrench with lighter hammer blows, or a regular 7/16 or 3/8 wrench (Whichever heads you have) with your thumb on the box to hold it on the bolt head and strike it with the heel of your hand a couple of times--ouch! This shocks the bolt a little at a time. Sometimes, they gall after you start them turning. So if you can get it to move at all, then rock it back and forth--each time going 1/8 turn or so further until it is loose enough that you know you won't twist it off.
Be aware that our friend heat may melt the seals so they would need to be replaced--but you were going to do that anyway--Right?
Also be aware that if the threads strip, three of the holes can be tapped deeper--actually all the way through the leg. The fourth hole is over the vent screw and can only be tapped about an inch deep. Murphy's Law--Guess which one will strip.
The three bolts tend to twist off at the top of the pump housing because the housing corrodes and grabs them tight. The one that gives the most trouble is the bolt over the vent screw--It twists off close to the lower unit casting. So you need to be most careful with this one. If any of them twist off and you can pry off the pump housing, then it is Vise-Grips and PB blaster time. If that doesn't work then it is drill and Heli-coil--but there is just enough meat there for it so that is a last resort.
