mini starter trouble

My nephew had a mini starter of his Ford Exploder off and bench tested 3 times at 2 part stores. Stick power to it and it would run. It woudn't start the engine though. When he called me I went over, pulled the starter laid in on the grond and zapped it with jumper cables. Yeah it ran. Wouldn't have ran a good fan though. I explained to him that this thing should start with so much torque that it would try to roll over. I should have needed to put a foot on it so it didn't toss the jumper cable clamps. Anyway... after all his grief a good starter was all he needed. As for yours , I'll assume the starter remained engaged to the flywheel and that's why the engine wont turn by hand.