Simplexes were selling well when the war ended, and 1948 was a big year for the little bikes. There were actually two models offered in 1948. The early model was the "48", so called because the engine serial number begins with "48" followed by the production number. This model was produced from October of 1947 through August of 1948.
From September of 1948 until January of 1949, the Model "J" Servi-Cycle was produced. There are minor differences between these two models.

Bennie Howard's Model "J"

ENGINE AND DRIVE SYSTEM

The Model 48 uses a next-generation kick starter which has a bolt hole near the center of the shaft instead of the U-bolt design. This is the first model to use the short muffler, which consists of a headpipe, a can-shaped muffler just ahead of and below the engine, and an outlet pipe of about five inches which exits down and to the rear. This is also the first model to use the wider rear wheel pulley (11/16" instead of 9/16"). This wider pulley design continues until the end of production in 1960.

Short style muffler used on 48, J, K, and L models.

Approximately 6100 bikes were produced in 1948. This was perhaps the largest production in a single year for Simplex, and was accomplished due to the opening of two additional plants, one in Baltimore and one in San Francisco. This was a short-lived operation which assembled units from components mainly produced at New Orleans; the tank decals reflected the location where the bike was built, replacing "New Orleans" with the appropriate city under the winged logo.