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24chick,
Most standard starter motors run "direct drive" i.e. the pinion gear turns at the same speed as the armature. High compression diesel engines often had trouble with this set-up so the manufacturers fitted a reduction gearset in the unit so that the pinion gear turned at say one third or one quarter of the armature speed, but with THREE or FOUR times the torque. Also, the solenoid that engages the starter is often mounted further away from the exhaust and is therefore less likely to suffer from heat soak.
I have heard that the GM gear reduction starter uses PLASTIC gears rather than steel, and might be best avoided because of this.