How to Choose the Correct Size Bearing
Jun 12, 2025|
Selecting the right engine bearings (main bearings and connecting rod bearings) is critical for engine performance and longevity. Here's a step-by-step guide to ensure you get the correct size bearings for your engine.
1. Measure Crankshaft Journal Dimensions
A. Use a Micrometer
Measure main journal and rod journal diameters at multiple points.
Check for:
Out-of-round (difference in diameter at the same position)
Taper (difference between ends of the journal)
Standard size example:
Main journal: 2.559" – 2.560" (65.00 – 65.02mm)
Rod journal: 2.098" – 2.099" (53.28 – 53.30mm)
B. Check Crankshaft Condition
Standard (STD) – No machining, original size.
Undersize (e.g., 0.010", 0.020", 0.030", 0.040", 0.050") – If the crank has been ground down.
A. Standard vs. Undersize Bearings
processing and testing equipment.
| Crankshaft Condition | Bearing Size Needed |
|---|---|
| Unmodified (STD) | Standard (STD) bearings |
| Machined (e.g., 0.010" under) | 0.010" undersize bearings |
| Severely worn (needs custom sizing) | Oversized bearings (rare) |
B. Check Bearing Clearance
Typical clearance:
Main bearings: 0.0015" – 0.0025" (0.038 – 0.064mm)
Rod bearings: 0.0010" – 0.0020" (0.025 – 0.051mm)
How to verify:
Use Plastigauge (plastic gauge) to measure installed clearance.
Measure with a dial bore gauge (more precise)
3. Choose Bearing Material
Aluminum (OEM, quiet, good heat dissipation)
Tri-Metal (copper-lead) (Performance, handles high loads)
Bimetal (steel-backed) (Economy rebuilds)
4. Final Verification Before Installation
✅ Check markings (STD, 0.010, 0.020, etc.)
✅ Test-fit bearings (use Plastigauge for clearance)
✅ Lubricate before assembly (use engine assembly lube)
Common Mistakes to Avoid
❌ Assuming all bearings are the same (Honda B vs. K series differ!)
❌ Mixing brands/types (e.g., Clevite mains with King rods
❌ Ignoring oil clearance (too tight = engine seizure, too loose = knocking)
Know your engine model and crankshaft size.Measure journals accurately .Select STD bearings accordingly!