Originally developed by MAHLE in the late 1960s, Nikasil is the trademarked name for nickel silicon carbide electroplate coating. Originally designed for the Wankel rotary engine, Nikasil is used on aluminum engine cylinders to eliminate the need for sleeves. A Nikasil-coated cylinder wall is diamond-hard, allowing aluminum pistons to glide inside the aluminum cylinder with matching thermal expansion characteristics with superior heat conductivity. Used by the likes of Porsche, BMW, Jaguar, and Ducati in the past, and now commonly used for marine, motorcycle, and extreme-performance race engines, Nikasil plating requires a different honing and machining process from typical cylinder bores.

YouTube Motorcycle enthusiast Chuck Harder recently visited Powersports Engine Solutions and shared a video of his tour to show the ins and outs of Nikasil machining and plating. One of the first things any engine builder needs to know about Nikasil-plated cylinders is that you cannot hone them with a traditional stone or dingleball hone. Nikasil is diamond-hard and requires a diamond hone, otherwise, you are creating a brutally rough finish inside the bore.

A stone hone cuts the nickel, but the silicon carbide remains. It may look cross-hatched, but it is actually just a very rough finish. “Nikasil is one of the hardest substances on the planet,” says Dana Kirby of Powersports Engine Solutions. When you look under a microscope, Nikasil is like a mountain range: lots of peaks and valleys. That helps it hold the oil, but it is not very smooth. When you run a stone hone over Nikasil, you are cutting the peaks of the nickel, but it just bounces over the silicon carbide. The silicon carbide has a Rockwell hardness of 90 or 95 and requires diamonds to cut it effectively.

The red line on the left of the screen is the shape of the bore, clearly not smooth, and it has a nasty taper.

Running a hone through a Nikasil cylinder is a useful way to determine its condition, as it immediately reveals the high and low spots, making it easier to assess the cylinder’s state and identify any areas that need attention. The only proper way to fix high and low spots in a Nikasil cylinder is by using a CNC boring machine, which can find and fix the high spots, taper, and out-of-roundness. In just 30 seconds, the diamond hone can remove about a half-thousandth-of-an-inch of material, so it is fast and effective. Nikasil coatings are typically about four-thousandths of an inch (.004) thick.

The cost of a hand-operated hone is around $600, and then you need diamond cutting blades, which can cost thousands. This means that you technically can hone them at home, but it comes with a significant cost that far exceeds what it costs to have them machined at a shop like PowerSports Engine Solutions, which has well over $100,000 in stones alone.

A cylinder that came in for honing and cleaning had marks under the top ring line and significant wear on the side and bottom, indicating a low spot that would cause oil burning, making it unusable, as-is. This can be repaired with honing and fresh Nikasil plating.

What Is The Nikasil Removal And Replating Process?

When an engine block comes in, it gets dipped in an acid that eats the Nikasil, but not the aluminum. You have to remove all of the steel from the block, as the acid will destroy everything that isn’t aluminum. Next, the aluminum block bore is honed in the CNC machine to diagnose the issues.

Next, the cylinder is dipped in nitric acid for about an hour to remove the Nikasil. This allows you to see the wear and damage, which can then be repaired. Because the cylinders are aluminum, the bore can be welded up and then honed to size and replated.

Much like chrome plating, Nikasil is an electroplating process, where the part is submerged in a chemical tank with only the cylinder bore exposed to the silicon carbide electrolyte fluid. Then, a nickel anode plate is placed inside the cylinder and connected to the positive pole, the cylinder is attached to the negative pole. Electricity flows through the fluid anode (nickel plate) and cathode (cylinder), leaching nickel ions, along with silicon carbide from the electrolyte, onto the cylinder surface. This process takes about an hour, depending on the desired Nikasil thickness.

The chemical baths strip away the old Nikasil, while leaving the aluminum bore unaffected. The bare aluminum cylinder is then replated in a specialized electroplating process.

Once plated, the part is removed, washed, and then put through the machining process, where it is brought back to final spec. The Nikasil coating is extremely tough and requires grinding down before honing, a process that takes around three hours of labor to complete, including stripping the old coating, recoating, grinding, and final honing.

Power Sports Engine Solutions aims to bring old-school plating and machining techniques into the modern era, not only to keep vintage Nikasil-plated engines in service, but also to improve the process and end products. Watch the full video here to learn more about Nikasil plating and repairs.