I've been meaning to do an article on this, but this will do until I can get pictures taken.
The screws on this cover are JIS cross heads, made from cream cheese I think!
Invariably, they are corroded into the cover and the cross wil rip out, even if you use the correct JIS screwdriver on them. Using an impact driver will guarantee this happenting, or the heads breaking off.
The heads with the ripped out cross can be drilled off, release oil put on the remains and usually the cover will lift off, leaving the stubs of the screws to be removed with a stud tool if they are really tight.
But sometime you can hit a problem.
On the left side of the transmission cover ( the right side as looking at the cover from the front of the engine) the outer screw goes into an 'ear' cast into the crankcase. This ear can relatively easily be broken off the cases if you get heavy handed with the screw removal.
That's not good!
I am in the process of rebuilding an engine for a customer and hit this problem, hence this post.
I tried everything I know, to release that screw!
It was so corroded into the cover that eventually, after spending 3 hours at it, I had to use the Dremel with a cutting disc and cut through the cover on both sides of the screw.
Brutal solution! But I had no choice. The cover had to come off to split the cases. You would not believe the corrosion between that screw and the cover.
Fortunately I have a spare cover and once the old one was off all the stubs came out fairly easily.
The problem with that particular screw is that the threaded hole in the crankcase ear is open to the elements from the rear. The solution, once you have replaced the screw with a new one, is to back-fill the hole with some epoxy sealer to keep any moisture out.
Before replacing the screws, make sure to run a tap down the threads to clear out any corrosion. You might be surprised how much rubbish you rmove out of each hole!
Make sure that you use a copper anti-seize on ALL the screws when replacing them. THIS IS ESPECIALLY IMPORTANT IF REPLACING THEM WITH STAINLESS STEEL ITEMS.