I remember reading a sci fi novel many years ago about a guy that finds a toroid and when he put a shaft in the middle it started rotating. He mounted it in an airplane and flew it to the moon. My ex sold my collection of old novels and I want to read this one again. I just don't remember the author or the title. Help?
I believe you are thinking of Moonbeast or The Beast by A E Van Vogt.
The hero - who has a missing arm - finds a strange engine on a hill. When he is experimenting with it he discovers that if he places a shaft into the centre of the engine it will spin. Different elements spin at different rates. There are a couple of strange effects - the shaft can only be pushed through the engine but not pulled and under certain circumstances the engine seems to negate gravity.
I have read parts of this book as a short story and there have also been a couple of novels with the same general premise but differing slightly in story line.
Having hit google for assistance, try http://filthycreations.proboards.com/thread/60/changling-beast-moonbeast-van-vogt - the chap there has a paragraph or two at the bottom that describes things better than I can.
Based upon the stories The Great Engine, The Changeling (aka The Wonderful Man) and The Beast. This cannibalised novel opens with The Great Engine - published many times as a short story. Pendrake finds the smooth metal doughnut-shaped alien engine on the hillside and takes it home for scrap. But there are others looking for the engine. The Lambton corporation is sending young couples to form a colony on Venus. As the plot segues into The Changeling, Pendrake’s arm has begun to regrow from the radiation of the engine - in fact he has begun to change into a superman, or 'toti-potent,' He is kidnapped by a group of armed women and taken to meet the President of the United States. These women, the President's personal corp, are 'equalised' women - they have taken the Makes You the Equal of a Man drug - which would doubtless have feminists today coughing as if they had fish bones stuck in their thr oats. Men find these 'equalised' women 'queer' and unattractive, while other women are uncomfortable around them.
Added as a clarification to user22225's apparently correct answer: the original story was titled "The Great Engine".