Our gear reduction starter motors have the same part number as Direct drive Starters but with -GR added to the end of the part number so EM427 is Direct drive and EM427-GR is gear reduction.
Direct drive and gear reduction are the two methods that a starter can use to drive the ring gear of a flywheel.
Direct drive came first, and it involves using a large, low speed motor to rotate a pinion gear in a 1:1 ratio.
Then came Gear reduction and entered mainstream usage about 20 years ago.
Unlike direct drive, gear reduction starters use smaller, faster motors to rotate their pinion gears in a roughly 4:1 ratio, which results in lower power consumption and higher torque.
When direct drive and gear reduction starters are compared, direct drive units are typically cheaper, and gear reduction units tend to be smaller, lighter, and more efficient.
In starters that use direct drive, the armature shaft of the starter motor is attached directly to the drive mechanism. Although “gear reduction” technically takes place between the starter’s pinion gear and the ring gear on the flywheel, the pinion gear itself rotates in a 1:1 ratio with the armature shaft.
Gear reduction is accomplished with spur or planetary gears.
A. Starters that use spur gears require an offset armature, this is
achieved by placing the starter drive in a separate gear
B. Starters that use planetary gears can be contained in an in
line drive-end housing.
In either case, the armature shaft will typically rotate about four times for each rotation of the pinion gear.
The advantage of gear reduction is that it allows for considerably smaller starters that produce a greater amount of torque in comparison to much larger direct drive starters. The main drawback is that they are typically more expensive.