SAE housing and flywheel dimensions should be understood by the mechanic, farmer, or DIYer as they are necessary to correctly identify tractor engine components for repair, engine replacement, or transmission replacement. SAE is an abbreviation for the Society of Automotive Engineers (SAE) and its standards or guidelines. SAE has many standards, and this tractor repair tip will touch on one SAE standard: the standard that provides guidelines on flywheel housings and dimensions.

For starters, where is this used?

According to SAE, “This SAE standard specifies major dimensions and tolerances for engine flywheel housings and coupling transmission housing flanges. It also locates the crankshaft flange face or bore stop face transmission pilot (or pilot bearing bore) relative to housing SAE flange face”

To fully understand this, let’s look at this example.

A customer wanted to remove a Fiat CP3 engine in a Laverda 152 Combine and replace it with a Perkins 1006.6. The first thing to be confirmed is whether the Perkins 1006.6 engine will be mated to the Laverda combine transmission. To do this, he compared the two SAE housing numbers. If the two SAE housing designations are the same, then the Perkins will bolt to the Laverda’s combine transmission. If not, then of course it will be a bad idea.

For example, an SAE casing brand might be SAE 21. This is a 12 threaded hole casing configuration, with specific dimensions. This SAE 21 number will be embossed or cast into the flywheel housing and transmission housing. Both will need to be SAE 21 for a perfect fit.

Standard SAE flywheel dimensions are designated by five measurements which, when compared, will specify an SAE number. These five sizes are XD, XB, XE, XF and XG.

XB is the casing outside diameter from one bolt pattern to the other bolt pattern, measured center to center.

XD is the outside diameter of the casing from the inside tip of the casing to the other. Similarly, the other abbreviations are similarly specified. A local Internet search for SAE Housing Dimensions can provide such a chart in an easy-to-print format.

These standards are used in their entirety by the main manufacturers of transmissions, engines and flywheels, such as Allison, Dana, Clark, Spicer, Rockwell, Fuller or Funk. It is therefore not surprising that these companies are OEM suppliers of transmissions, engines, and flywheels to most of the world’s largest engine and transmission manufacturers.

So the next time a situation arises to change your engine or transmission, compare the SAE designations before you buy or start your repairs.