Though I'm not aware of stated starter motor cycle limits for the 172, I would, none the less suggest that it is possible to overheat and damage a starter motor with continued cranking. By way of example, I can tell you that many piston engines, and small turbines have starter motor limitations like: 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 seconds waiting, 30 seconds cranking, 30 MINUTES waiting. It is possible to melt armature windings when over working starters....
For the Lycoming IO-360 the recommended starter duty cycle is:
Crank the starter for 10 sec followed by a 20 sec cool down period. This cycle can be repeated 2 times, followed by a 10 minutes cool down period before resuming crancking. After cool down, you can repeat these 3 cycles of 10 sec followed by 20 sec cool down.
