Pro Piston Set | 2RZ & 3RZ

• 1995.5-2004 2RZ 2.4L Engines (Boosted)

CP Forged Piston Set 

Cylinder Honing Specifications (CPN & CPN2 Rings)

For engine builds utilizing CP Pistons CPN and CPN2 piston rings, achieving the correct cylinder wall finish is critical to ensure rapid ring seating, optimal oil retention and maximum compression sealing.

• Honing Method: Plateau Honing
• Target Cross-Hatch Angle: 35-40 degrees

Following these exact parameters ensures proper micro-texture on the cylinder walls, which reduces friction while maintaining an adequate oil film.

Recommended Honing Media & Finishing Procedures

To achieve the required surface roughness targets on gray cast iron engine blocks or Nikasil cylinders, honing equipment manufacturers recommend a two-stage process using specific abrasive grits.

Stage 1: Initial Honing Abrasives

Select one of the following stone types to establish the baseline cross-hatch pattern and depth: 

• Conventional Stones: #220-#280 grit
• Diamond Stones: #325-#550 grit

Stage 2: Plateau Finishing

After the initial hone is completed, you must smooth the cylinder walls to eliminate jagged peaks, folded metal, and torn material left behind by the coarser stones. Finalize the bores using one of these three methods:

• A fine-grit conventional abrasive (#400-#600 grit)
• A sweep of the bores using a flexible honing brush
• A specialized nylon-bristle plateau honing tool

Technical Note: Always verify with your honing equipment manufacturer that your specific stone grits will accurately produce the required surface roughness targets:

Rz Surface Finish: 59 - 138 μin (1.5 - 3.5 μm)
Ra Surface Finish: 15 - 35 μin (0.4 - 0.9 μm)

CP Piston Ring End Gap Recommendations

Critical Safety Note: Failure to properly check and set the piston ring end gap can result in catastrophic engine failure.

The guidelines provided below are general industry recommendations. The optimal ring gap varies significantly depending on your specific engine configuration and application. Enhanced clearances are typically required for high-stress environments, including forced induction (turbocharged or supercharged), nitrous oxide systems, filled blocks, and endurance racing. Determining and verifying the final correct end gap is the sole responsibility of the engine builder. 

For additional technical support, please contact customer service directly at 949-567-9000.

How to Calculate Your Ring End Gap

To determine your required ring end gap, first locate your specific driving application in the target specification chart.

-Note: All metric cylinder bore measurements must be converted to inches before applying the gap factor.

Step-by-Step Calculation

1. Convert Bore to Inches: Divide the metric bore size (mm) by 25.4.
2. Apply Application Factor: Multiply the resulting bore size in inches by the specific application clearance multiplier provided in your spec sheet.

Example Calculation (81mm Bore for a Standard Street Application):

• Step 1: 81mm / 25.4 = 3/189 inches
• Step 2: 3.189 x 0.005 = 0.016" target end gap

Piston Ring Specifications & Gap Measuring Procedures

The following instructions outline the standard technical procedures for verifying piston ring end gap. Because high-performance or specialized applications may require unique clearances, always consult the included engineering charts and diagrams prior to final installation.

Step-by-Step Ring Gap Measurement

1. Torque Plate Installation: If applicable to your specific engine build, install a torque plate onto the block and torque it to factory specifications. This simulates true cylinder distortion and bore roundness during actual engine operation.
2. Squaring the Ring: Carefully insert the piston ring into the cylinder bore. Ensure the ring is positioned below the deck surface and completely square to the bore walls. (See Figure 1)
3. Measuring the Gap: Insert a precision feeler gauge (or an equivalent ring-gap measuring tool) into the gap to measure the distance between the ring ends. (See Figure 2)

-Important: If your measured ring gap is less than the minimum specification required for your specific bore size, it will be necessary to file-fit the rings to achieve the proper end gap. Failure to do so can cause the ring ends to butt together under thermal expansion, leading to severe cylinder scoring or catastrophic engine damage.

Piston Ring Filing Procedures:

When file-fitting your piston rings, accuracy and correct technique are critical to ensure a proper seal and prevent cylinder damage.

• Use the Right Equipment: Always use a dedicated manual or electric piston ring-gap filing tool.
• Filing Direction: Always file the ring end in an inward direction (from the outside face of the ring toward the inside). Filing outward can chip or damage premium outer coatings.
• Keep it Square: Ensure the ring ends remain completely square and parallel to one another during the filing process.

-Bore Size Note: Performance ring sets are manufactured to precision tolerances for specific bore diameters. For every 0.001" the cylinder bore is oversized or worn beyond its intended specification, the ring end gap will naturally increase by 0.00314".

Compression Ring Installation & Orientation

Before installing your compression rings, closely inspect the ring faces and edges for markings, bevels, or grooves.

Top Compression Ring:

• Marked Rings: If the ring features a dot, laser etching, or writing, always install the ring with this marked side facing UP toward the cylinder head.
• Unmarked Rings with an Inner Bevel: If the ring is completely unmarked but features a cut bevel along the inside edge, install the ring with the bevel side facing UP toward the cylinder head.
• Completely Unmarked/Uniform Rings: If the ring has no dot, writing, or inner bevel, it is symmetrical and can be installed with either side facing up.

Second Compression Ring Installation & Orientation

Before installing the second compression ring, carefully inspect the ring faces and edges for markings, grooves, or bevels. Proper orientation is essential to ensure effective oil control and prevent compression blow-by. Install the ring according to the following guidelines.

• Marked Rings: If the ring features a dot, laser etching, or writing, always install the ring with the marked side facing UP toward the cylinder head.
• Taper Hook Groove Style (Scraper Ring): If the ring features a taper hook groove along its outer edge, the groove must always face DOWN toward the oil pan. (See Figure 4)
• Unmarked Rings with an Inner Bevel: If the ring is completely unmarked but features a cut bevel along the inside edge, install the ring with the bevel side facing DOWN toward the oil pan. (See Figure 5)
• Completely Unmarked/Uniform Rings: If the ring has no dot, writing, hook groove, or inner bevel, it is completely symmetrical and can be safely installed with either side facing up.

Oil Ring Installation & Specifications:

Most CP Pistons oil ring assemblies utilize a three-piece design consisting of two thin steel rails and a center expander ring. Proper installation is critical to ensure optimal oil control and prevent cylinder wall scoring.

• Rail End Gap Clearance: Ensure the end gaps in both the upper and lower oil rails are a minimum of 0.015".
• Rail Alignment: The ends of the rails must never butt together or overlap during installation. 
• Expander Modification: Do not cut, file, or modify the center expander ring in any way. The expander relies entirely on its factory-engineered tension to properly support the rails and maintain correct tension against the cylinder wall.

Product Disclaimer & Limitation of Liability

Due to the extreme stresses and severe operating conditions inherent in high-performance and racing environments, all CP pistons/Pankl products and services are sold strictly "as is" and "with all faults."

Exclusion of Warranties

There are no warranties, express or implied, given for these products. This includes any implied warranty of merchantability or fitness for a particular purpose.

As a core condition of doing business and part of the bargain of sale, the purchaser expressly agrees that they assume all risk. The purchaser takes full responsibility for selecting, testing, and verifying that the parts are appropriate for their specific application. CP Pistons/Pankl provides all buyers with a complete opportunity to inspect and examine all parts, inventory, and services prior to purchase and installation.

Limitation of Liability

CP Pistons/Pankl shall not, under any circumstances, be held liable for any special, incidental, or consequential damages. This strict limitation of liability includes, but is not limited to:

• Damage to, or operational failure of, other engine components, property or equipment.
• Loss of anticipated profits, business revenue, or commercial opportunities
• Costs associated with down time, labor or acquiring replacement goods.
• Third-party claims made against the purchaser by their own customers.
• These liability exclusions apply absolutely to any and all outcomes resulting from the sale, installation, modification, or track use of these high-performance parts.