the starter motor just spins, does not engage the flywheel. The belts & pulleys only spins a little.
the sarter motor engages but does not turn the flywheel, starter just spins on 1993 Infiniti J30
check you'r stater to see if the starter is engaging the flywheeel. Sounds like there could a few teeth are missing from the starter or the flywheel. If you just purchased a new or used starter, check again to see if the starter is the right starter for you'r vehicle.