Borded out with an 1-1/2 hole saw and cutting oil. Get a good one not a cheap one. I have a Lenox kit that I used. Go slow and be careful when you punch through or you will hit the cylinder wall. The hole saw will center nicely in the stepped hole. Then smooth the walls of the holes with a round sanding wheel and a die grinder. Then tap by hand. This is a tedious process! It will take all day. It took me over an hour per hole x 7.
I ordered the plugs from Fastenal. You will likely have to have them ordered as not many places will stock these.
I borrowed the tap. I'm looking to buy a whole kit up to 1-1/4 now as I need them periodically, but yes they are expensive.
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