I have found out thru another member that these engines were manufactured for the G. H. Tennant Company.
Web search came up with this,
Founded in 1870 by George H. Tennant, Tennant Company began as a one-man woodworking business, evolved into a successful wood flooring and wood products company, and eventually into a manufacturer of floor cleaning equipment. Throughout its history, Tennant has remained focused on advancing its industry by aggressively pursuing new technologies and creating a culture that celebrates innovation. Today, Tennant is a global leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world.