Rotating Cylinder Liners: Searching For Reduced Piston Ring Friction

Friction is the enemy of every engine. It robs power, increases wear, and burns more fuel. According to Lake Speed, Jr. — a.k.a. The Motor Oil Geek — a significant portion of this friction — about 40 percent — comes from the interaction between piston rings and cylinder walls. These two components alone are responsible for almost half of the total friction inside an engine. So, how can rotating cylinder liners REDUCE friction?

That’s where Lake Speed Jr. comes in. A leading expert in tribology (the science of friction and lubrication), Lake is passionate about finding ways to reduce friction and improve engine efficiency. In a recent discussion, he delved into a revolutionary engine design—a rotating cylinder liner—that takes lubrication science to the next level.

Understanding the Three Stages of Lubrication

To explain how lubrication works in an engine, Lake uses a simple analogy: water skiing.

Boundary Lubrication:

“If the boat is not moving, the water skier is submerged in the water and that’s the boundary condition, essentially,” says Speed. “There is no hydrodynamic wedge, there’s no fluid film to support the skier, he sunk in the water.”

Mixed Lubrication: 

“As the boat begins to pull the skier out of the water, you’re somewhat dependent upon the velocity of the boat lifting that ski,” Speed explains. “That skier’s gear, the water ski, and the life jacket are still supporting some of that skiers load.”

Hydrodynamic Lubrication:

“Once the boat reaches enough speed, now it’s got the full film,” says Speed. “It’s the fluid effect of that relative motion between the ski and the water that’s supporting the load of the skier.”

Every engine experiences all three lubrication stages during operation. Piston rings go through this cycle with every stroke, which means friction and wear are unavoidable — or at least, they used to be.

Why Piston Rings Cause So Much Wear

Inside a running engine, the piston rings move up and down thousands of times per minute. The problem? They don’t always stay in the hydrodynamic lubrication phase.

The most efficient condition for a piston ring and the cylinder wall is in the middle of the piston’s stroke. “At mid-stroke, the piston is moving quickly. There is very little pressure behind it, so the piston ring rides in a nice film of oil, no friction, no wear,” Speed explains

As you approach top dead center or bottom dead center, you start to change conditions, and friction increases dramatically. “Coming to the top of the cylinder, the pressure goes up, the speed goes down,” explains Speed. “So from about minus 30 degrees before top dead center to about plus 45 degrees after top dead center in a typical engine, the piston rings start touching the liner and grinding against the liner, increasing the friction coefficient by a factor of 10, perhaps more.”

Once the piston comes to a stop and changes direction, you reach the maximum point of both friction and wear between the two surfaces. “Exactly at top dead center, the connecting rod is perfectly perpendicular, but slightly after top dead center, you have the peak cylinder pressure and the combination of the peak cylinder pressure and the angularity of the connecting rod creates a very high contact force between the piston skirt and the cylinder,” Speed elaborates.

The result? More wear at the top of the cylinder than in the middle. This is why engines lose performance over time — the rings are constantly wearing down the cylinder walls, increasing friction and oil consumption.

Rotating Cylinder Liners

cylinder liners

That’s where Speed introduces a game-changing innovation: a rotating cylinder liner. Instead of the liner staying still while the piston moves, the liner spins at a controlled speed. This does two major things. The first is reducing metal-to-metal contact. “By rotating the liner, you’re moving the piston rings out of boundary condition,” speed explains. That rotation keeps the piston ring lubricated with a hydrodynamic wedge, even at zero vertical piston speed. “The idea is you’re rotating this liner and you’re doing it in series at constant speed,” says Speed. 

The Stribeck Curve

Speed references the Stribeck Curve, a graph that shows how friction changes with different lubrication conditions. The key takeaway? Friction is highest in the boundary phase and lowest in the hydrodynamic phase. By making the liner rotate, the engine spends more time in hydrodynamic lubrication and less time in boundary lubrication. This means less wear, lower fuel consumption, and better overall efficiency.

How Much Friction Does This Actually Reduce?

Dr. Dimitri Dardalis, an expert in tribology, helped test the rotating liner engine under real-world conditions. The results were significant. Friction was shown to be reduced to 0.8 bar at 7 bar IMEP. He also espouses the fuel savings offered, saying, “At idle, the engine is going to be consuming about 40 percent less fuel.” That fuel saving is extrapolated into potential cost savings. “In a tiny little engine like this operating as a generator, you can be saving $50,000 a year without too much trouble,” says Dr. Dardalis. 

Why This Matters for Engine Longevity

Every time an engine runs, its piston rings are fighting friction. Over time, this leads to increased oil consumption, loss of power, and eventual rebuilds. By introducing rotating cylinder liners, the engine doesn’t just last longer — it runs more efficiently from day one. This breakthrough has real-world applications in everything from racing engines to commercial fleets. Less friction means less wear, more power, and better fuel economy.

Speed is passionate about turning lubrication science into real-world performance gains. His work on piston ring friction and engine efficiency proves that even small innovations — like a rotating line — can make a huge impact on how engines perform.

As Speed himself says, “This is like tribology in action, and I love tribology. This is so freaking cool. This is amazing. It’s an engine focusing on tribology. Most engines focus on the thermodynamic side. Here, we’re only focusing on the tribological side of the engine, leaving the thermodynamics exactly the way it came from the factory.”

For anyone looking to maximize engine efficiency, reduce wear, and save money on fuel and maintenance, this innovation is worth paying attention to. The idea of rotating cylinder liners is a game-changer in friction reduction — and now, thanks to Lake Speed, Jr. and Dr. Dimitri Dardalis, the science proves it.

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