Connecting Rod Bearing Selection

Important: If crankshaft bearing failure is due to other than normal wear, investigate the cause. Inspect the crankshaft and the connecting rod bearing bores.

Notice: Do not shim, scrape, or file bearing inserts. Do not touch the bearing surface of the insert with bare fingers. Skin oil and acids will etch the bearing surface.

1. The connecting rod bearings are of the precision insert type. The connecting rod bearings are available in standard and 0.25 mm (0.0098 inch) undersize. Undersize refers to crankshaft diameter. The undersize bearings are marked with red paint (1).
Standard Connecting Rod Bearing Size: 1.355-1.365 mm (0.0534-0.0537 inch)
Standard Crank Pin Diameter: 49.982-50.000 mm (1.9678-1.9685 inch)
0.25 mm (0.0098 inch) Undersize Connecting Rod Bearing Size: 1.605-1.615 mm (0.0632-0.0635 inch)
0.25 mm (0.0098 inch) Undersize Crank Pin Diameter: 49.732-49.750 mm (1.9580-1.9586 inch)





2. Measure the connecting rod journal for taper (3 minus 4) and out-of-round (1 minus 2).
Maximum Crankshaft Taper: 0.01 mm (0.0004 inch)
Maximum Crankshaft Out-of-Round: 0.01 mm (0.0004 inch)
3. Regrind or replace the crankshaft if the taper or out-of-round exceeds specifications.

Notice: Refer to Fastener Notice in Service Precautions.

4. Install the connecting rod cap to the rod and tighten the nuts to 45 Nm (33 ft. lbs.).
5. Measure the connecting rod bearing bore for taper and out-of-round.
6. No taper or out-of-round should exist. If taper or out-of-round exists, replace the connecting rod.





Important: The crankshaft and the lower crankcase assembly must be installed and properly torqued before measuring the connecting rod clearances.

7. Starting with the number one connecting rod, remove the connecting rod cap nuts.
8. Remove the connecting rod cap by wiggling the connecting rod cap left and right.





Important: Do not turn the crankshaft while the gauging plastic is installed.

9. Lay a piece of gauging plastic across the crankshaft connecting rod journal (avoiding the oil hole).
10. Carefully place the connecting rod cap onto the connecting rod. The arrow on the rod cap should point towards the front of the engine.
11. Install the two connecting rod cap nuts.
Tighten the connecting rod cap nuts to 45 Nm (33 ft. lbs.).
12. After reaching the proper torque, remove the two crankshaft connecting rod cap nuts.
13. Carefully remove the connecting rod cap from the connecting rod.
14. Measure the gauging plastic at its widest point.
Standard Oil Clearance: 0.039-0.057 mm (0.0016-0.0022 inch)
Maximum Oil Clearance: 0.08 mm (0.0031 inch)
15. If the oil clearance exceeds the maximum replace the bearing with a new standard size bearing.
16. If the oil clearance exceeds the maximum with a new standard size bearing replace the crankshaft or regrind the crankshaft. Regrind the crankshaft. Regrind the crankshaft so that the finished crankpin diameter equals the measured connecting rod bore diameter minus 0.048 mm (0.0018 inch).





17. Install a new 0.25 mm (0.0098 inch) undersize bearing to the connecting rod.
18. Install the connecting rod cap and torque the nuts to 45 Nm (33 ft. lbs.).
19. Measure the connecting rod bore diameter with the undersize bearing installed.
20. Measure the crankpin diameter.
21. Ensure that the oil clearance is within specifications.