Flexible Hones for Nikasil Liners and Engine Rebuilds

Nikasil is a nickel-plated, silica carbide coating that’s sometimes applied to the inner walls of engine cylinders. Invented by MAHLE in 1967, Nikasil reduces friction and wear, especially in aluminum bores. Nikasil liners improve oil retention and are thinner, lighter, and harder than cast iron or carbon coatings; however, some engine builders avoid this high-performance plating material. Because Nikasil coatings are thin, rigid hones such as honing stones can remove too much of the lining.

Some hobbyists also claim you can’t deglaze Nikasil cylinders, but ball hone users know better. Made by Brush Research Manufacturing (BRM), the Flex-Hone® is a flexible, resilient honing tool that features nylon filaments permanently laminated to ball-like abrasive globules. Self-centering, self-aligning to the bore, and self-compensating for wear, BRM ball hones aren’t designed for heavy-duty material removal. Instead, these engine hones improve surface finish – even with very hard materials such as Nikasil.

Cylinder Deglazing and Surface Finishing

In gasoline or diesel engines, the reciprocating movement of the pistons can create a glaze on cylinder walls. If this finish is too smooth, the piston rings will skate along the surface and fail to seat and seal properly. Cylinder wall glazing can also prevent engine oil from adhering to surfaces. During engine rebuilds then, Flex-Hone® tools are used to break the glaze and impart a surface finish with oil-retaining valleys for optimum lubrication and reduced engine wear.  Note, however, that Flex-Hone® tools are not recommended for ported nikasil cylinders.

At on-line forums, engine mechanics have described their use of BRM glaze breaker hones. For example, a motorcycle mechanic explained using flexible honing tools to deglaze the Nikasil-plated cylinders in a Kawasaki ZRX 1200 engine. Other bikers have documented their use of BRM ball hones in engine rebuilds for BMW motorcycles. At Thumper Talk, an on-line forum for dirt bike enthusiasts, users discussed Flex-Hone® tools for Nikasil liner preparation and debated which type of abrasive to use.

Abrasive Types and Flexible Honing

Flex-Hone® tools are available in a wide variety of abrasive types and grits to meet a range of surface finishing challenges. For Nikasil cylinders, BRM recommends cylinder hones with aluminum oxide (AO) abrasive. Nikasil-coated bores are easier to over-hone than cast iron engine cylinders, for which silicon carbide (SC) is the right choice. The Flex-Hone® Resource Guide provides complete information about how to select the right abrasive types and grit sizes for different base materials.  

As members of Thumper Talk learned from a peer, it’s important to choose the right cylinder hone and then use it correctly. When one user incorrectly claimed that flexible honing would remove too much material and fail to impart a cross-hatch pattern, another mechanic posted before and after pictures of an engine cylinder. The Flex-Hone® tool that this user chose imparted a plateau finish with a cross-hatch pattern of oil-holding valleys. A picture, they say, is worth a thousand words.