Re: Mercury 1150 powerhead removal question
The studs towards the back look pretty rusted, so I'd venture the cavities in the exhaust tower where the studs pass thru are packed with corrosion. This binds up the studs and keeps the powerhead from coming off.
If you tap on each stud with a metallic object such as a combination wrench, any stud that's free will "ping". Any stud that resounds a dull "thud" is stuck. You can also gently pry sideways to see if the stud will 'give', any one that doesn't give a little bit is stuck.
One way to get them loose is to heat the sides where the stud passes thru, with a propane or MAPP etc torch. Pry on the very front studs as suggested while heating the back studs, this'll help. As will thin wedges. Note: don't use a screwdriver, the surface area is too small and it'll gouge the sealing surfaces of the block and exhaust tower.
Another method I've used before on badly-stuck studs: run a nut back up one of the studs, except upside-down so the Nylock part faces up (or pick up some regular, fine-threaded non-locking nuts).
Grab a pile of 3/8" flat washers and stack onto the open end of the stud, up against the nut. Keep on stacking until the washers extend to the end of the stud. Then, using a chunk of steel, more washers, whatever is handy, fill up the rest of the space between the end of the stud and the structure below.
What you're going to do is use the stud as a "jacking bolt" by wrenching the nut on the stud downwards into the stuff you've used to create a "shim" below the stud.
This applys way more pressure than you could ever apply by 'wedging' and will force the stud (and the powerhead attached to the stud) upwards.
You may need to set up jacking points on both sides and on more than one stud per side. Combined with heat and prying from the front studs, I'll just about guarantee you'll bust that powerhead loose. If she don't come loose then, just break out the Plastique!!!!
HTH & let us know how it goes............ed
