SL2017-645/JNN Fretting/Corrosion in Main Bearing Bore

This service letter gives important information regarding development of fretting/corrosion on main bearing caps. In service, we occasionally observe fretting/corrosion between the main bearing shell and the main bearing cap on engines without main bearing temperature sensors.

This service letter gives important information regarding development of fretting/corrosion on main bearing caps.
In service, we occasionally observe fretting/corrosion between the main bearing shell and the main bearing cap on engines without main bearing temperature sensors.

The fretting/corrosion is caused by relative movement between the bearing shell and cap during engine operation. The result is that water and oil can migrate between the bearing shell and cap through the sensor hole and cause the observed wear patterns on the bearing running surface.

As the extent and development of the observed corrosion are related to the presence of water in the lube oil, we recommend keeping the water content at an absolute minimum at all time, reference is made to SL13-582.

In case fretting/corrosion on the bearing cap is not addressed, it may cause severe engine damage due to bearing failure.

If you have any questions or comments, please forward your mail to This email address is being protected from spambots. You need JavaScript enabled to view it. with reference to this service letter.