ISO 18669-2:2025

Overview

ISO 18669-2:2025 - "Internal combustion engines - Piston pins - Part 2: Inspection measuring principles" defines the measurement principles used to inspect piston pins for reciprocating internal combustion engines. It applies to piston pins with a nominal outer diameter (OD) from 8 mm to 100 mm and is intended for road-vehicle engines and other applications (with agreed modifications where appropriate). The standard complements ISO 18669-1 (general specifications) and aligns inspection methods with GPS and NDT practices.

Key topics and technical requirements

• Scope and applicability: Measurement rules for piston pins (OD 8–100 mm); adaptable for non-road applications with purchaser/manufacturer agreement.
• General measuring conditions:
  • Instrument resolution ≤ 10% of the tolerance of the measured dimension.
  • Measurement uncertainty to follow ISO 14253 series.
  • Measurement systems analysis reference: AIAG / IATF 16949.
  • Reference temperature for OD: 20 °C ± 1 °C.
  • Apply the principle of independence per ISO 8015.
• Outside diameter (OD):
  • Reference method: precision caliper with spherical probes (radius 1.0 mm) applying ~1 N force.
  • Stated measurement uncertainty: ±0.0005 mm (per ISO 14253).
• Form and surface characteristics:
  • Cylindricity: Multiple polar diagrams per ISO 12180-2 (least-squares reference cylinder, Gaussian filter, stylus tip radius 1.0 mm, UPR 1–50).
  • Circularity: Polar macro-form per ISO 12181-2 with similar parameters.
  • Circumferential waviness, edge drop-off, concentricity (ID vs OD), runout, end-face features, surface roughness, case depth, hardness and material defects are defined with measurement principles or referenced test methods.
• NDT and hardness references: Links to ISO 9934 (magnetic particle), ISO 15548 (eddy current), ISO 16810 (ultrasonic), and hardness standards (ISO 6506/6507/6508).

Applications and users

ISO 18669-2:2025 is used by:

• OEMs and engine builders for production and incoming inspection of piston pins.
• Tier-1/2 suppliers manufacturing pins and components for internal combustion engines.
• Metrology laboratories and quality-engineering teams implementing inspection measuring principles, measurement uncertainty and measurement systems analysis.
• NDT and failure-analysis teams assessing material defects, case depth and grinder burn.
  Typical uses: production quality control, supplier agreements, design validation, R&D and root-cause analysis.

Related standards

• ISO 18669-1:2021 (Piston pins - General specifications)
• ISO 12180-2 (Cylindricity), ISO 12181-2 (Roundness)
• ISO 14253 (Inspection by measurement)
• ISO 21920 series (Surface texture)
• ISO 9934, ISO 15548, ISO 16810 (NDT methods)
• ISO 6506/6507/6508 (Hardness tests)

Keywords: ISO 18669-2:2025, piston pins, inspection measuring principles, internal combustion engines, outside diameter, cylindricity, circularity, measurement uncertainty, GPS.