I have an electric cooktop so my method is slightly different (my new house will have gas so I'll have to try this way ).

First of all , put the new bearing in it's packet in the freezer.


Second, I strip the engine as in the above post and when all I have left is the block (even wthout the carb retaining bolt or anything else except the block and the two bearings), I set the oven to 250 degrees C and put the block in as soon as I turn on the oven. I monitor the oven so I know when it clicks off meaning it has reached 250C.

At this point I remove the bearing from the freezer and put it on the crank.

Keep in mind the block is now rocket hot so wear an oven mit!!

Take the block from the oven with the mit and knock it on the bench (I use an old wooden cutting board to keep the missus happy) and the bearing will fall out. Keep a pair of longnose pliers handy as it may not fall all the way out and you will need to grab it.

Next, while you still have the hot block in your hand, drop in the crank and new bearing. Use the sharp end of a wooden spoon to seat the new bearing, and you're done.

If anything doesn't seem like it's seated right, just heat the block again and remove the bearing or push the crank in further.

Hope this helps.