How are you heating it Kostas ? The only way that works for me is to put it in the oven until it's hot enough for spit to ball-up and roll off. Be aware though that the female of the species will go into orbit if she catches you spitting into the oven !
Have you removed all the cover studs ? You really need to do that so that you can take hold of it in your gloved hands and give the case a good hard thump on a block of wood.
The sleeve gear bearing tends to fall out under its own weight but the layshaft bearing does need shocking.
Hi Kostas,
Rik has some good advice. There have been times with stubborn bearings that I turn up a wooden (oak) drift on my lathe. Good & hot, remove, insert drift, give it a whack or two. To me, it beats dropping the casting.
No worries about the female of the species for me. I live alone for a reason after buying two houses for them. Now, I work on bikes for me. Even in the living room if I want! 