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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.
About the
Author
This CR4 blog entry originally appeared in
the BRM
Flex-Hone Blog.
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