Nope, aluminum with chrome liner..The cylinder alloy is different, theoretically expands a little more than the piston..The engines were used in 400 lb drones, cruised around for 5 or 6 hours running at 7000 rpm on gas, ported and timed for economy..We run 9400 rpm using methanol and glow plugs...We're not pushing the engines hard enough, the glow plugs lasted for 2 years and were still in the engine when the spinner hit the prop and the plane crashed at about 200 mph..Nothing left of the engine, but the glow plugs still work McCoy #9s.....Fuel was FAI with about 8 oz oil to a gallon.....
The thermocouple twisted wires stick out about 1/2 inch from the flange, right in the exhaust...