Standard SAE Flywheel Dimensions and Its Application to Tractor Repair

SAE Housings and Flywheel Dimensions needs to be understood by the mechanic, farmer, or DIY individual, as its necessary to correctly clarify tractor engine elements for repair, engine substitute, or transmission replacements. SAE is an abbreviation for the Society of Automotive Engineers (SAE) and their standards or guidelines. SAE has many standards, and this tractor repair tip will touch on one SAE standard-the standard that provides guidelines on housings and flywheel dimensions.

To begin with, where is this used?

According to SAE, “This SAE Standard specifies the major dimensions and tolerances for Engine Flywheel Housings and the Mating Transmission Housing Flanges. It also locates the crankshaft flange confront or the transmission pilot bore (or pilot bearing bore) stop confront in relation to housing SAE flange confront”

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

A customer wanted to remove a Fiat CP3 engine on a Laverda 152 Combine, and replace it with a Perkins 1006.6. The first item that needs to be confirmed is if the Perkins 1006.6 engine will bolt onto the Laverda combine’s transmission. To do this, he compared the two SAE housings numbers. If the two SAE housings Designations are the same, then the Perkins will bolt onto the Laverda’s combine transmission. If not, then of course, this will be a bad idea.

For example, a SAE housing mark can be SAE 21. This is a 12 tapped hole housing configuration, with specific dimensions. This number SAE 21 will be embossed, or casted onto the flywheel housing, and the transmission housing. Both will need to be SAE 21 for there to be a perfect fit.

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

XB is the external diameter of the housing from one bolt pattern to the other bolt pattern, measured from center to center.

XD is the external diameter of the housing from the internal tip of the housing to the other. Similarly, the other abbreviations are similarly stated. A local search on the internet for SAE Housing Dimensions can provide such a chart in an easy printable format.

These standards are fully utilized by all major transmission, engine, and flywheel manufacturers such as Allison, Dana, Clark, Spicer, Rockwell, Fuller or Funk. It’s not surprising consequently, that these companies are OEM transmission, engine and flywheel suppliers for most of the world’s largest manufacturers of engines and transmissions.

So, the next time a situation comes up to change your engine, or your transmission, compare the SAE designations before buying or beginning your repairs.

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