I recently purchased a new distributor cap and rotor, both need to be replaced. The ignition is a Thunderbolt System. I unscrewed the four screws that hold down the cap and replaced the cap but was not able to replace the rotor. Any ideas how to remove the rotor? I assume you just pull up; however this had no effect on removing the rotor. There is a stainless steel cover which is fastened to the bottom of the rotor with three screws. Do I need to remove these three screws before pulling the rotor?