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What is a Nikasil Sleeve in the Mercury Racing Outboard?

Nikasil® is a common term used to describe a cylinder bore that has been plated with nickel silicon carbide, and then finished to a precise bore diameter and very specific finish.

Silicon carbide is an extremely hard ceramic material and requires a honing process using diamond hone tooling. Due to this extremely hard surface, the cylinder wall will have very strong wear properties over time.

In Mercury Racing outboard engines, Nikasil sleeves are often used to line the cylinders in the 245 HP Carb, 260 EFI, 280 ROS, and 300 Drag.

This coating is known for its hardness and wear resistance, which helps to maintain cylinder shape and prevent excessive wear, even under high-performance conditions.

It's a popular choice in high-performance engines like those used in racing or high-speed boating applications because it can withstand the stresses and heat generated by these engines better than traditional cylinder materials.

Under normal use from combustion, there will be a buildup of carbon and burnt oil on the bore surface known as “glaze”. Glaze will prevent the rings from properly seating during the break-in process, therefore it needs to be removed.

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