The Importance of Light Checking Piston Rings and Verifying Oil Control Ring Tension During Engine Break-In

Proper piston ring seating during engine break-in is essential for ensuring optimal performance and longevity. In engines with Nikasil-plated cylinder bores, this process is even more critical due to the unique properties of the Nikasil surface. Our latest YouTube video walks through the steps for light checking piston rings and verifying oil control ring tension to achieve a perfect break-in. Here’s a detailed guide based on the video.

Why Proper Cylinder Preparation Matters

Nikasil-plated bores are highly durable, but they do not wear in the same way as iron cylinder bores. Proper surface preparation, including achieving a plateau hone, is critical for ensuring the rings seat correctly. If the surface finish or cylinder concentricity is off, the rings may take longer to seat—or fail to seat entirely. This can be verified with a profilometer, in this case a Mitutoyo SJ-210 using Traceboss software.

Likewise, cylinder geometry must be verified using a bore gauge to ensure cylinders are within tolerance with no more than .002" of ovality and taper.

Step 1: Light Checking Piston Rings

Light checking involves ensuring the rings create a light-tight seal with the cylinder walls, confirming proper fit and sealing potential.

1. Preparation:

   • Ensure cylinders are properly honed and cleaned.
   • Gap the piston rings according to specifications.

2. Performing the Light Check:

   • Place the piston ring in the cylinder bore.
   • Shine a light behind the ring and inspect for light passing between the ring face and the cylinder wall.
   • A light-tight fit indicates proper contact and sealing.

3. Key Considerations:

• Top Rings: These are typically OD-lapped and rarely fail the light-tight test unless the ring size is incorrect.
• Second Rings: These are critical for secondary oil control. If they fail the light-tight test, the engine may experience increased oil consumption and smoke.
• Oil Control Rings: Light checking is not necessary, but radial tension is an important factor to verify.

Step 2: Measuring Oil Control Ring Tension

Proper oil control ring tension ensures effective oil management and prevents excessive consumption or blow-by.

1. Setup:

   • Clean and lubricate the cylinder and the oil control ring.
   • Install the oil control ring onto the piston and fit it into the cylinder.

2. Measuring Tension:

   • Use a fish scale, luggage scale, or trigger pull scale to measure the force required to move the piston through the cylinder.
   • Focus on measuring the constant force (not the breakaway force) applied during the movement.

3. Target Tension for Nikasil Bores:

   • Low-tension piston rings are common in modern engines, with an average radial tension of 8 lbs compared to 20 lbs for standard rings.
   • For Nikasil bores, aim for approximately 10 lbs of radial tension, as tension typically drops by 1 lb after break-in.

4. Adjusting Tension:

   • Experienced builders can fine-tune tension by swapping out rails or modifying oil rail expanders.
   • Applications may require more or less tension depending on specific engine requirements.

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Why These Steps Are Essential

• Light Checking: Ensures optimal ring seal, critical for compression and oil control during engine break-in.
• Verifying Tension: Prevents over- or under-tensioning, which can lead to oil consumption issues or ring failure.

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Final Thoughts

By light checking your piston rings and verifying oil control ring tension, you set the foundation for a successful engine break-in. These steps are especially important for engines with Nikasil bores, where surface preparation and precision are non-negotiable.

Regardless of whether or not you are rebuilding an aircooled or watercooled Porsche engine, be sure to download AND read out detailed Porsche engine assembly and break-in procedures and guidelines.

For a detailed walkthrough, watch our video: Light Checking Piston Rings and Verifying Oil Control Ring Tension. If you have any questions or insights from your own experience, leave a comment—we’d love to hear from you!

Watch the Video Now!