How hot?

why not , jim :?: Valve seats , are just the same, a steel ring shrunk into alloy. My suggestion is a last ditch ,for mains that refuse to "just" fall out. plus the wife will be happy not having a crank case smoking in the oven,and tainting the apple pie :lol:

Why would you put the crankcase into an oven ? - over a gas jet is much simpler. This stuff is not rocket science. Shrinking a valve seat to remove it might require the use of a stick welder because the diameter is so small and the amount of shrinkage is proportional to that. The main bearings in a Norton commando are so large that relatively low heat on aluminium cases is enough to give a large differential expansion and easily release the bearing.

Since I started this my comment would be 'not everyone has a welder at hand' but most have a
oven. Not everyone has a gas cook top these days either. Buying a mapp gas torch is not big money
so that is a more likely tool.
Im not saying my question was about the best way or even the correct way it was about the way
available to me.
At my point in life I dont really want to be adding new tools as much as I like them. First it is a welder
and the next thing the wall is being knocked out to get the Bridgeport in.
Slippery slope and all that.
Many thanks for your comments.

john robert bould said:

why not , jim :?: Valve seats , are just the same, a steel ring shrunk into alloy. My suggestion is a last ditch ,for mains that refuse to "just" fall out. plus the wife will be happy not having a crank case smoking in the oven,and tainting the apple pie :lol:

Click to expand...

I guess for about 20 years I have had an industrial oven in the shop -so no pies to worry about.
Before that I had a cheap [free] pizza oven that I used.
I have never had a Norton bearing that didn't fall out -usually before the cases ever got to 300 degrees.

I use the TIG welder for valve seats. Jim