Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Understanding the SAE J2873 Standard for Electric Cooling Fan Motor Mounting
SAE J2873 was a recommended practice issued in 2010 and cancelled in 2016 that provided standardized mounting interface dimensions for attaching electric cooling fan motors to fan shrouds in light duty vehicles. This article reviews the standard’s specifications, engineering insights, and the reasons for its cancellation.
Standardized Mounting Dimensions
SAE J2873 defined three families of bolt circle diameters for attaching electric cooling fan motors to fan shrouds. All mounting holes were spaced at 120 degrees and had a 6 mm diameter. The table below summarizes the key dimensions:
| Bolt Circle Size | Diameter (mm) | Mounting Hole Diameter (mm) | Spacing (degrees) |
|---|---|---|---|
| Small | 100 | 6.0 | 120 |
| Medium | 120 | 6.0 | 120 |
| Large | 170 | 6.0 | 120 |
These sizes were intended to cover approximately 85% of supplier and OEM applications. The small bolt circle typically applied to low-power 2-pole motors under 150 W, the medium to 4-pole motors from 150 to 500 W, and the large to high-power motors exceeding 500 W.
Engineering Design Insights and Industry Impact
The development of SAE J2873 involved input from various suppliers to create a common basis for communication. 🛠️ By standardizing just three families, the practice aimed to balance the need for uniformity with the reality of diverse applications. However, the standard was cancelled in March 2016 because the industry found it “unnecessary and limiting to innovation.”
⚠️ Important Note: SAE J2873 is a cancelled Technical Report. Engineers should not reference it as a mandatory requirement. The cancellation reflects a shift toward allowing more flexibility in fan motor mounting designs, enabling innovation and customization beyond the prescribed bolt circles.
Despite its cancellation, understanding the standard can be helpful when evaluating legacy designs or when a common baseline is desired for supplier communication. The standard cross-references SAE J635 for fan hub bolt circles and pilot holes.
🛠️ Design Insight: The three size families were not arbitrary. They corresponded to typical motor power ranges and provided a simple solution that covered the vast majority of light duty vehicle cooling fan applications. This pragmatic approach allowed engineers to quickly select an appropriate mounting interface without over-engineering.
Now that the standard is cancelled, engineers are free to choose mounting interfaces that best suit their performance, cost, and packaging requirements. However, existing designs that follow J2873 dimensions may still be reused or adapted, especially if interchangeability with existing components is needed.
Frequently Asked Questions
- What are the standardized bolt circle diameters for electric cooling fan motors?
- SAE J2873 defined three bolt circle diameters: small (100 mm), medium (120 mm), and large (170 mm), all with 6 mm mounting holes spaced at 120 degrees.
- Why was SAE J2873 cancelled?
- The SAE Cooling Systems Standards Committee cancelled the standard because industry found it unnecessary and limiting to innovation. The recommended practice was seen as restricting design freedom.
- What percentage of applications did the three sizes cover?
- The standard was designed to cover approximately 85% of both supplier and OEM applications, balancing standardization with needed variety.
- What alternatives exist now that this standard is cancelled?
- Engineers can now design fan motor mounting interfaces without adhering to the J2873 dimensions. They may adopt custom bolt circles, use fewer or more bolts, or integrate mounting features in novel ways. However, for legacy compatibility or supplier alignment, the J2873 dimensions may still be used as a reference.
For more details, refer to the cancelled document available from SAE International and the related SAE J635 standard.
