A can of compressed air upside down makes a "freeze spray". For a stubborn crank bolt, I used a propane torch targeting the washer part of the crank bolt, I'd heat then try and break about four times in a row, then I'd hit the end of the bolt itself with the freeze spray for 20 seconds or so, then try and break it again. Theory was, metal expands when heated, shrinks when cooled. So try and heat the socket and area around it, then rapidly cool just the bolt. In theory, that would help the surfaces move independently and break any bonds from corrosion, and make the slightly shrunk bolt easier to remove from the slightly enlarged hole. Must have done something right, because it did the trick. Also worked on the stuck flywheel bolts.
I did all that with the first screw. Except for the HIGH QUALITY PH3. The LOW QUALITY PH3 twisted and stripped the Philips head. I then bought a PH3 connected to a socket housing. I heated them, put the PH3 on there, attached the socket wrench, applied some UMPF and they turned right off. Except for one more that just stripped like butter. These are some SOFT screws.Glad it came right off. A big ole impact wrench is invaluable. That looks like corrosion on the oil pump cover screws. How did you go about trying to remove them? a quality PH3 Bit? light taps with hammer to seat the bit into the screw? impact driver? those three things help alot with painless removal.
We used them a lot when I worked on electric commuter trains. Talk about high torque and break away tightness in confined places.Personally, 4X torque multiplier has worked on every one, with ease. A good investment if you’re going to do it more than once. It truly makes it a breeze.