CYLINDER HEAD GASKET 27-11745M

Function and technical context

The head gasket is the hermetic sealing element that seals the interface between the engine block and the cylinder head, guaranteeing the tightness of the combustion chamber and cooling ducts. In Yamaha two-stroke marine engines of the 40 hp series, this gasket works under extreme conditions of pressure and temperature, preventing combustion gases from escaping to the outside and the coolant from entering the chamber. Its correct function is absolutely critical: poor sealing causes power leaks, water entering the crankcase, progressive overheating and, ultimately, seizure or catastrophic engine failure.

When to replace this part?

A worn head gasket manifests itself with symptoms such as progressive loss of compression, difficulty starting when cold, presence of water or emulsion in the oil, visible coolant leaks at the block-head joint, and abnormal overheating of the engine even when cruising at moderate speed. Although there is no fixed hour interval, it is recommended to inspect its condition during each seasonal inspection and replace it preventively if the engine accumulates more than 800-1000 hours of operation or if you detect any of the above symptoms. Replacing this gasket preventively is significantly cheaper than repairing an engine with cooling damage or seizure.

Engine Compatibility

Mercury/MerCruiser

Equivalent manufacturer part numbers