Flywheel turns but motor doesn't!!! Help!!!

[Stangbanger86]

Allright, I thought i had a starter problem on my car so I finally got around to changing it. Well when i cranked it, it made the same noise. Like the starter is spinning but the motor wasn't. I was pissed, it was late, and I had to be up early the next morning. So I went over in my head what it could be. I thought maybe the flywheel teeth were worn. So I got under the car, found a place to look at the flywheel and watched it turn as my buddy cranked it. What the hell can it be a cracked flywheel?? Well I'm ready to pull everything off and change it, could it be anything else!!!!!!!! Help!!!!!!!!!!