I have a Marks lock on my iron door, I never got a key for it so I was trying to take the lock off to get it rekeyed, but I can't the lock off the door. I took all strews off but the lock cylinder won't come out of the door. Is there anyway to get this out?

The cylinder can be removed by loosening the set screws that hold it in position. These screws are located in the lock front or faceplate and are accessible when the door is open. Once the screw is loosened the cylinder should turn freely and it can be unscrewed from the lock body by turning it counterclockwise. Use a blank key or a small flathead screwdriver to remove the cylinder. Do not try to remove the cylinder by turning the collar. It will spin independently from the cylinder and the cylinder will not turn at all.