How Does the Engine Mount to the Transom?
Typically four bolts are used to mount an outboard motor to a transom. Generally, with a new engine, the manufacturer supplies the mounting hardware. The hardware is usually stainless steel machine screws of 1/2-inch diameter and threaded with the standard 1/2-13NC thread pitch. It is also seen that machine screws with finer pitch, 1/2-20NF, are used. On some engines the mounting screws may be metric fasteners of similar strength and size. When replacing hardware use mounting screws of proper size and strength. Stainless steel fasteners are highly recommended to avoid corrosion. Stainless steel threads should be protected against galling by application of a thread compound. (For more details on this problem see this article by Joe Greenslade.) The mounting bracket of the engine typically is designed for two upper mounting bolts and two lower mounting bolts, arranged symmetrically about the engine centerline. The upper set of mounting holes is typically provided in a series of four (or
