Identifying your SAE Flywheel Size

An SAE flywheel size identifies the standardized dimensions of an engine flywheel used to help match power transmission components such as a power take-off (PTO) to the engine. When selecting an industrial PTO, the engine’s SAE flywheel and flywheel housing dimensions are two of the primary specifications used to determine proper fitment.

SAE flywheel and housing configurations are commonly referenced using standards such as SAE J620 and SAE J617. Identifying the correct flywheel size typically requires measuring several physical dimensions, including the pilot diameter, bolt-hole arrangement and spacing between mounting holes.

In this guide, we’ll walk through the basic measurements needed to identify your SAE flywheel size so you can compare them with the appropriate sizing chart and provide accurate information when selecting a PTO.

SAE Flywheel Dimensions can be measured in a combination of different ways, including: drive ring pilot, bolt circle, housing face to flywheel, pilot bearing bore, bolt circle diameter, quantity, and hole-to-hole measurements.

1. Start by counting the number of tapped holes on the flywheel and measuring the diameter of the hole (dimension G).
2. Measure the distance from the center of one tapped hole to another. This measurement will provide the Hole-to-Hole measurement.
3. Measure the pilot diameter in the flywheel (dimension D).

Use the chart as a guide to determine what SAE Flywheel you have. Contact a WPT Sales Representative or Applications Engineer for further assistance.

Why is SAE flywheel size important when selecting a PTO?

SAE flywheel size helps determine whether a power take-off will properly fit the engine and flywheel housing. PTO selection commonly depends on the engine’s SAE flywheel and housing dimensions, along with other application requirements such as torque, horsepower, operating speed, engagement method and drive configuration.

Using the correct SAE flywheel size helps ensure that the PTO mounting dimensions, drive ring and related components are compatible with the engine. If the flywheel size or housing configuration is uncertain, measuring the flywheel before selecting a PTO can help prevent fitment problems and incorrect component selection.