Go to a electric motor repair/rewind shop tell them what you want they may give/sell you a brush large enough to get a piston out of or in my case 10 pistons.
Gary
I built one years ago the power piston is graphite in an acrylic cylinder seems to work.. the displacer shaft is just a hole in long (1 inch) acrylic, brass shaft. Runs best on a bowl of ice. (Built from a photo)
I have tried all of the suggestions that I have found here. None have helped. I use two different android boxes using up to date versions, neither will stay logged in.
Gary
On aircraft engines we take the plugs out hot every year or 50 hours very rarely is there a problem. When they go back in we use a grafite based antisize sold by Champion and torqued with a calibrated tool. I think the special spark plug antisize is the key.
Gary