Pro Piston Set | 2RZ & 3RZ

• 1995.5-2004 3RZ 2.7L Engines

CP Forged Piston Set

Cylinder Honing Quick-Reference

Achieving the correct cylinder wall finish is critical for rapid ring seating, optimal oil retention, and maximum compression sealing. When preparing a gray cast iron engine block or Nikasil cylinders for CP Pistons CPN and PCN2 high-performance ring sets, ensure your machine shop follows these exact specifications.

To achieve the required surface roughness targets on a gray cast iron engine block or Nikasil cylinders, equipment manufacturers recommend a two-stage honing process: 

Stage 1: Initial Honing 

Use either of the following stone types to establish the baseline cross-hatch pattern.

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

Stage 2: Plateau Finishing

After your initial hone with either conventional or diamond stones, you must smooth the cylinder walls to eliminate jagged peaks, folded metal, and torn material. Finish the bores using one of the following methods.

• Fine-Grit Abrasive: Use a fine-grit conventional abrasive (#400-#600 grit).
• Flexible Brush: Sweep the cylinder bores with a flexible honing brush.
• Plateau Tool: Use a 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

The guidelines provided below are general industry recommendations. The optimal rung gap varies depending on your specific engine configuration and application. Enhanced clearances are required fir high-stress environments, including forced induction (turbocharged/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.

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

How to Calculate Your Ring End Gap

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

Conversion Formula & Example

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 factor 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 = 0.0016" target end gap

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

Piston Ring Installation & Gap Measuring Procedures

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

Step-by-Step Ring Gap Measurement

1. Torque Plate Installation: If applicable to your engine build, install a torque plate onto the engine block and torque it to factory specifications to simulate true cylinder distortion.
2. Squaring the Ring: Insert the piston ring into the cylinder bore. Ensure the ring is positioned below the deck surface and completely square to the bore.
3. Measuring the Gap: Use a precision feeler gauge (or an equivalent ring-gap measuring device) to measure the distance between the ring ends.

-Important: If your measured ring gap is less than minimum specification required for your specific bore size you must carefully 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 engine damage.

Piston Ring Filing Procedures:

When file-fitting piston rings to achieve the proper end gap, accuracy is critical. Incorrect filing techniques can damage the ring surface or cause improper cylinder sealing.

Step-by-Step Filing & Orientation Guidelines

1. Use the Correct Tool: Always use a dedicated manual or electric piston ring-gap filing tool. Never use a standard hand file or grinder.
2. 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 the premium outer facing or coatings.
3. Squaring the Ends: Ensure the ring ends remain completely square and parallel to one another during the filing process.
4. Top Face Orientation: Before final installation, check the ring faces for any markings: 

• -If the ring has a dot or laser-etched writing, install the ring with this marked side facing UP toward the cylinder head.
• -If the ring features a taper hook-groove style (scraper ring), ensure the hook groove faces DOWN toward the oil pan.

Bore Size vs. Ring Gap Expansion:

Performance ring sets are manufactured to precision tolerances for specific bore diameters. For every 0.001" the cylinder bore us oversized or worn beyond the intended specification, the ring end gap will naturally increase by 0.00314". Always measure your exact cylinder bore before modifying your rings.

Oil Ring Installation:

Most CP Pistons oil ring assemblies consist of a three-piece design: two thin steel rails and one center expander ring.

• Rail End Gap Clearance: Ensure the end gaps on both the top and bottom oil rails are a minimum of 0.015".
• Rail Alignment: The rail ends must never butt together or overlap during installation.
• Expander Care: Do not cut, file, or modify the center expander ring in any way. The expander relies on its factory-engineered tension to properly support the rails and control oil flow.

Product Disclaimer & Limitation of Liability

Due to the extreme conditions inherent in high-performance racing and engine applications, 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, including any implied warranty of merchantability or fitness for a particular purpose. It is expressly understood and agreed between CP Pistons/Pankl and the purchaser-as a core condition of doing business and part of the consideration of sale-that the purchaser accepts full responsibility for selecting, inspecting, and purchasing all products. CP Pistons/Pankl provides the purchaser with a full and complete opportunity to examine all parts, inventory, and services prior to use or installation.

Limitation of Liability

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

• Damage to or loss of other property or equipment.
• Loss of profits, revenue, or business opportunities.
• Costs associated with purchased or replacement goods.
• Claims made by the purchaser's customers or any third party.

These limitations apply to any and all claims that may arise from, or result from, the sale, installation, modification, or use of these parts.