91 240sx ka24de Wont start! Need help ASAP!

[xOWNEDGEx]

i just bought a 1991 240sx and was told the starter was bad, which it was got it benchtested, i got a used starter and bench tested it and it was good, so i put it in, and when i try to start it engages for a sec and turns the engine a little but then it disengages and just spins, i dont know much about 240's could it be a starter relay or starter solenoid?

[S13_RB25]

When you say it spins, do you mean it spins freely or what?? If so then that starter is also bad. I had brand new on put it and the lock, thats holds the teeth on the rod that engages and disengages it, broke on it. So it would spin freely. So I took it out and stuck a screw driver in it and the rod it self spun but the teeth didn't spin at all...