Overview
ISO 13778:2017 - "Plain bearings - Quality assurance of thin-walled half bearings - Selective assembly of bearings to achieve a narrow clearance range" - provides guidance for selectively assembling thin-walled half bearings (in accordance with ISO 3548‑1) to control and reduce bearing diametral clearance. The standard addresses the combined effect of housing diameter, journal diameter and bearing wall thickness (tolerance “stack up” typically 50–60 µm), and describes grading and matrix schemes to achieve tighter clearances required for modern engine refinement.
Key topics and requirements
- Selective assembly principles: Methods to combine graded components so the effective diametral clearance meets a narrower specified range.
- Clearance calculation: Theoretical diametral clearance C = D_H – (2·s + D_J), where D_H is housing diameter, s is half-bearing wall thickness, and D_J is journal diameter.
- Tolerance stack up: Recognition that housing, journal and bearing tolerances accumulate; typical stack-up and need to reduce range for improved NVH and performance.
- Housing swell & thermal expansion: Effects of interference fit, bolt torque and material (e.g., light alloys) on bore expansion; guidance to measure and allow for swell and thermal effects.
- Measurement & identification: Accurate metrology (micrometre-level) for housings, journals and bearing crowns; practical marking methods (colour codes, bar/dot coding, etching) and data storage for assembly.
- Grading schemes: Six example fitting schemes increasing in complexity and precision:
- Scheme 1: No grading (standard process capability)
- Scheme 2: Bearings graded only
- Scheme 3: Bearings and journals/housings graded
- Scheme 4: Unmixed bearings (matrix scheme) - narrowest range example
- Scheme 5: Mixed bearings (matrix scheme)
- Scheme 6: Mixed bearings (fine matrix) - micrometre-level selection
- Trade-offs: Narrower clearance ranges require tighter component tolerances, more complex logistics and inventory control; schemes may be suitable for OEM assembly but impractical for aftermarket replacement sets.
Applications
- Used primarily in internal combustion engine main and rod bearing assembly where improved refinement and reduced bearing clearance are required.
- Applicable to bearing manufacturers, engine OEMs, assembly engineers, quality and metrology teams, and powertrain development groups planning selective assembly programs.
- Helps reduce NVH, optimize oil film performance and extend bearing life by controlling clearance distributions.
Who will use this standard
- Bearing suppliers implementing grading and identification processes
- Engine manufacturers designing assembly and quality assurance procedures
- Quality engineers developing measurement and tolerance control plans
- Metrology labs specifying measurement methods for housings, journals and bearing crowns
Related standards
- ISO 3548-1 - Thin-walled half bearings: tolerances, design features and methods of test (normative reference)
- ISO 4378-1 - Terms, definitions, classification and symbols for plain bearings
Keywords: ISO 13778:2017, plain bearings, thin-walled half bearings, selective assembly, bearing clearance, bearing grading, housing swell, tolerance stack up, matrix scheme, quality assurance.
