[3][4] The SY features the JF6s lacked included taller smokestacks, different front step and handrail arrangements, different motion bracket arrangements, a higher boiler pressure (210 psi (1,400 kPa), a lower axle loading (15 tonnes (33,000 lb), and all boxpok driving wheels.

[3] The prototype SY (SY-0001) was constructed in 1960, by the Tangshan Locomotive and Rolling Stock Works, and thirteen others followed suit that same year.

[7] By 1966, the SY design became finalized with some standardized changes, including a widened cab, and commercial production on the class began.

[1] In service, all of the SYs were assigned to shunt and haul freight trains in numerous industrial areas throughout China, including coal mines, iron ore mines, petroleum fields, chemical plants, power stations, steel mills, and machine factories.

[3] Sometime during production, the SY class received a new tender tank design with sloped-back sides to improve rearward vision for crews, since SYs often operated in reverse, during industrial service.

[12] After the end of commercial steam operations on Chinese main lines in 2005, some SYs still remained in service for some industrial firms, such as the Sandaoling Coal Mine Railway in the Xinjiang Uyghur Autonomous Region.

In 1989 and 1991, three SYs were constructed for tourist railroads in the United States, SY-1647M ('M' Chinese: 美国; pinyin: Měiguǒ; lit.

142 ran throughout the NYS&W system until its transfer to the New York Susquehanna & Western Technical & Historical Society in 2003 and now operates on the Belvidere and Delaware River Railway in Phillipsburg, New Jersey.