Nikasil Cylinder Honing: Special Techniques
Nikasil Cylinder Honing: Special Techniques, Tool Selection & Practical Tips
Nikasil coatings require specialized tools. This guide explains why standard Flex-Hone® tools fail on Nikasil – and which solution actually works.
At a Glance
- Nikasil (nickel-silicon carbide) is a galvanic hard coating on aluminum cylinders
- Hardness: approx. 58–62 HRC – only diamond tools work reliably
- Standard SiC Flex-Hone® tools are virtually ineffective on Nikasil
- Primary applications: BMW motorcycles, Porsche engines, high-end KTM/Husqvarna cylinders
- Goal: Renew the cross-hatch finish without damaging the coating
What Is Nikasil?
Nikasil is a patented galvanic coating process in which a nickel matrix with embedded silicon carbide particles is applied to the inner wall of an aluminum cylinder. The result is an extremely hard, wear-resistant bore surface that is significantly lighter than a pressed-in cast iron cylinder liner.
Advantages of Nikasil
- Very high hardness (58–62 HRC)
- Excellent wear resistance
- Superior heat dissipation compared to cast iron
- Lower weight (no liner required)
- Tighter piston clearances possible
Challenges
- Sensitive to high-sulfur fuels
- Not repairable – only re-coating possible
- Standard honing tools are ineffective
- Higher cost compared to cylinder liners
- Incorrect machining destroys the coating irreversibly
Background: Nikasil was developed by Mahle in the 1970s and first used in Formula 1 engines. Today it is employed by manufacturers such as BMW (R-series motorcycles), Porsche (air-cooled 911s), KTM, Husqvarna, and many other OEMs. The coating typically lasts 100,000+ km – provided it is not damaged by improper machining.
Which Abrasive for Nikasil?
Nikasil is not a homogeneous hard material but a nickel matrix with embedded silicon carbide particles. What matters is therefore not which grain is hardest, but what you are trying to achieve. Deglazing opens up the glazed running surface so the piston rings seat again – deliberately removing almost no material.
| Abrasive | Use | Assessment |
|---|---|---|
| Aluminum oxide (AO), grit 240 | Deglazing before a re-ring | The manufacturer's recommendation – opens the surface without attacking the thin coating |
| Silicon carbide (SC) | Deglazing, more aggressive | Works as well; tool life approx. 8–15 cylinders instead of 15–30 on cast iron |
| Diamond (CD) | Material removal | Only where material genuinely has to come off – oversized for deglazing |
The most common mistake is not the wrong abrasive but honing for too long. The Nikasil layer is only 0.05–0.08 mm thick. Break through it and the aluminium underneath is exposed – the cylinder then has to be re-plated or replaced.
Warning: Never attempt to hone a Nikasil cylinder with sandpaper, reamers, or coarse honing stones! These tools can locally remove the coating, which is only 0.05–0.08 mm thick, exposing bare aluminum. The cylinder would then be irreparably damaged.
Diamond Flex-Hone® for Nikasil
Brush Research Manufacturing has developed the Diamond Flex-Hone® series specifically for Nikasil and other hard coatings. Instead of SiC or AO, industrial diamond particles are embedded in the globule matrix.
- Grit: Typically 600 (20 µm) or 800 (15 µm) for finishing, 320 (40 µm) for heavier material removal
- Construction: Identical to the standard Flex-Hone® – globe-shaped abrasive balls on flexible nylon filaments
- Designation: “D” in the part number (e.g., GBD-xxx instead of GB-xxx)
- Tool life: Longer than SC tools on hard surfaces, because diamond wears significantly more slowly
Cost perspective: Diamond Flex-Hone® tools cost approx. 3–5x more than standard SC tools. However: a single diamond tool processes more Nikasil cylinders than 10 SC tools – which don’t work on Nikasil at all. Per cylinder processed, diamond tools are therefore more economical.
Step-by-Step: Honing a Nikasil Cylinder
Check the coating for chipping, scoring, and discoloration. If the Nikasil layer has been locally removed (visible aluminum), honing is pointless – the cylinder needs re-coating or replacement.
Diamond Flex-Hone® (GBD) in the appropriate size. Oversize: approx. 15–20 % of the bore diameter. For most motorcycle cylinders (60–100 mm): GBD size approx. 70–120 mm with 600 or 800 diamond grit.
Nikasil requires more coolant than cast iron. Use mineral honing oil (no WD-40, no brake cleaner!). The surface must remain wet throughout the entire process.
RPM: 200–400 for typical motorcycle cylinders. Insert the tool into the bore with the machine running, stroke evenly. Processing time: 20–40 seconds.
Uniform cross-hatch pattern visible? Surface consistently satin-matte? Then the cylinder is ready for assembly. If spots appear bare or uneven → hone for 10–15 more seconds.
Common Mistakes and Their Consequences
| Mistake | Consequence | Prevention |
|---|---|---|
| Used standard SC Flex-Hone® | No material removal, tool spent after one use | Use only Diamond Flex-Hone® (GBD) |
| Worked with honing stones/steel wool | Nikasil coating locally removed, cylinder destroyed | Never use abrasive materials without globule geometry |
| Too coarse grit (80–240) | Coating damaged, deep grooves instead of fine cross-hatch | Minimum 320 grit, preferably 600 or 800 diamond |
| Honed dry | Thermal damage, diamond globules glaze over | Always use generous amounts of honing oil |
| Honed a damaged cylinder | Wasted time – honing cannot repair chipping | Visually inspect first, assess coating condition |
Nikasil vs. Cast Iron Cylinder Liners: What It Means for Honing
| Property | Nikasil Cylinder | Cast Iron Cylinder Liner |
|---|---|---|
| Tool | Diamond Flex-Hone® (GBD) | Standard Flex-Hone® (SC/AO) |
| Grit | 320–800 Diamond | 120–400 SiC |
| RPM | 200–400 RPM | 300–600 RPM |
| Processing time | 20–40 sec. | 30–60 sec. |
| Error tolerance | Low – irreversible damage possible | High – forgiving material |
| Tool cost | Higher (Diamond) | Lower (SiC) |
| Repairability | Re-coating only | Reboring + new liner possible |
For a complete step-by-step guide to honing cast iron cylinders, see Cylinder Honing: DIY Guide. The procedure described there serves as the baseline – for Nikasil, you simply switch to a diamond tool.
Diamond Flex-Hone® at PrecisionPro Shop
| Category | Diameter | Products | |
|---|---|---|---|
| Specialty Flex-Hone® (Diamond) | 4–200 mm | GBD series, all grits | Browse Range |
| Standard Flex-Hone® (for cast iron) | 4–610 mm | SC, AO, BC Volume pricing | Browse Range |
Conclusion: Nikasil Honing = Use Diamond
The core message of this article is simple: Nikasil coatings must only be honed with Diamond Flex-Hone® tools. Anything else wastes time and risks expensive damage. Invest in the right tool (GBD series), use ample honing oil, and work at moderate RPM (200–400). Then you’ll achieve a flawless cross-hatch finish even on Nikasil – and the cylinder will be ready for thousands more kilometers.
FAQ
How do I know if my cylinder has Nikasil?
Nikasil cylinders are made of aluminum (lightweight, silver-colored housing) with a yellowish-silver, mirror-like inner surface. In contrast, cast iron liners have a matte, dark gray bore surface. If you have a BMW boxer, Porsche flat engine, KTM single, or Husqvarna motor, Nikasil is very likely. If in doubt: check the manufacturer’s documentation or consult an engine builder.
Can I hone Nikasil with a Boron Carbide Flex-Hone®?
Boron carbide (BC, Mohs 9.5) is harder than SiC but still significantly softer than diamond. It works marginally on lightly worn Nikasil surfaces but has a short tool life and does not produce consistent results. For reliable, reproducible results, we recommend diamond – it’s worth the investment.
My Nikasil cylinder has dull spots – can honing fix that?
Dull spots can have two causes: a) surface deposits (carbon, oil coke) → these disappear during honing, or b) worn-through coating → the exposed aluminum is irreparable and won’t improve with honing. Check: if the dull spot appears darker or copper-colored, the coating is gone. In that case: re-coating or replacement cylinder.
How much does a Diamond Flex-Hone® cost compared to standard tools?
Diamond Flex-Hone® tools are priced at approx. 3 to 5 times the cost of a standard SC tool of the same size. For typical motorcycle cylinder sizes (75–100 mm), expect an additional €40–80. Keep in mind: an SC tool on Nikasil is worthless – it produces zero material removal. The extra cost for diamond is therefore not optional but a necessity.
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