In August of 1928, Harley-Davidson introduced the 1929 "D" model for the sale price of $290.00, the first in a line of the three year "DL" series. Harley had to compete with other competitor's established middleweight motorcycles such as the Indian 101 Scout and the Excelsior's Super X and therefore forcing the birth of the now famous "45" motor. It was offered as a "D" with a 4.3:1 low compression ratio, the "DL" with a higher compression ratio of 5:1 (introduced in September of 1928), also the "DLD" Special Sport Solo model and the "DS" sidecar version. To rationalize production, H-D placed their new motor in their 30.50 cu. in. "C" model bike but changed the wheel diameter from 20 inches to 18 inches. Due to the fact the motorcycle's frame had a straight downtube, the generator was mounted on the engine vertically just in front of the forward cylinder, running off a bevel gear. Because of this funny configuration the bike was nicknamed "The Three Cylindered Harley". Unfortunately many problems plagued the first model. These included : a small 3/4 inch carburetor venturi (which restricted performance), generator drive train failure after low mileage, the oil slot in the end of the crankshaft was extended out too far into the bearing (causing insufficient oiling), the oil pump didn't supply oil at high speeds, and the front forks were to short and not very strong causing misalignment. Many of the problems were addressed by September of 1928 and solved by engine number 29D3404. Due to the ongoing concerns of mechanical failures, H-D discontinued the 1929 "D" and "DL" series in the Spring of 1929 until the release of the 1930 models in August of the same year. Overall H-D had put out an impressive machine when compared to the fact that Excelsior and Indian had a couple years to work out their flaws before the introduction of the "45".

Not too many accessories were offered during the production years of the "DL" compared to today's standards, but they did include : a Corbin speedometer, rear luggage rack, front stand, carry on tools, ride control for the front fork springs, a steering damper, a windshield, a tandem seat for a passenger and a sidecar produced by Goulding Litecar, manufactured in Saginaw, Michigan. In 1934 more accessories were offered such as: mirrors, parking lights, rear stop light switch and the buddy seat to replace the tandem seat.