Dando: The thermal expansion of aluminum is greater than steel. This means the aluminum case holding the bearing will expand more than the steel bearing when they're heated. When changing bearings in 2/4 stroke motors, the aluminum case is heated, not frozen. Years ago, prior to my transition to electric, I used a 300 degree oven to heat the engine crankcase. Afterwards, the bearings would normally just drop out of the crankcase. Suggest you place the Plettenberg backplate/bearing in the oven for a while and heat it. Alternatively, you can use a propane/butane torch to heat the aluminum. You shouldn't need to apply the heat for too long, just long enough to get the aluminum hot. The bearing should be much easier to remove. When you install the new bearing, get the aluminum hot and the new bearing should slip right in.

Mike