Heavy Duty Alternator

Tech Tip: Understanding Starter Motor Mounting

Did you ever wonder why motor mounting holes are larger in size than the fasteners?
To understand, you must first look at the starting motor mountings for heavy duty diesel engines. Manufacturers use either a SAE Type 1 or a SAE Type 3 drive housing.

Regardless of the mounting style, each starting motor drive housing has mounting holes that secure the motor to the engine bell housing or the transmission with the use of fasteners. The holes’ sizes may vary from model to model and among manufacturers.
On the drive housing, there also is a mounting register that aligns the motor in place for proper pinion-to-ring-gear mesh. The tolerance for the mounting register is much closer to the engine-mating surface in order to provide the correct positioning.
The larger mounting holes allow the motor to align and be positioned with the register for proper operation. It does not negatively impact performance in any way.
Watch our short Tech Tip video to learn more about motor mounting holes.

YouTube Link to Video
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