Usage:
All Caterpillar Engines
Fretting is the transfer (movement from one to the other) of material between two surfaces which make contact with each other. During fretting, material breaks away from one surface and becomes fused (fastened together by heat) to the other surface.
It is caused by small but rapid movement of the contact surfaces, like main bearings and caps or saddle bores, or connecting rod bearings and rods or rod caps. This rapid movement is permitted by oversize bores, cap bolts which are not tightened correctly and/or not enough bearing crush. Decreased bearing crush and oversize bores that permit fretting will come as a result of normal engine use.
Fretting generally takes place on the most heavily-loaded bearing half. For example, the material probably will be on the lower main bearings and bearing caps, or the upper rod bearings and connecting rods. Also, steel from the bearings generally transfers to the cast iron surfaces of the main bearing caps and/or saddle bores.
When a bearing has been damaged by fretting, the fretting material must be removed before the installation of new bearings.
Fretting in main bearing and cap.
First, use only a pencil grinder to remove the fretting material from the surfaces. When fretting material is removed from a main or connecting rod bearing bore, make sure all of the material is removed. It is better to remove a very small amount of the component surface than to have some fretting material left on the surface. Even a very small amount of fretting material left on a surface can decrease the oil film between the bearing and surface, which can cause damage to the new bearing.
Clean the area with a brush, soap and water to remove all debris.
After a pencil grinder has been used to remove the fretting material, use a 1P3537 Dial Bore Gauge to measure the bearing bore to make sure it is in specifications. This must be done with the caps installed and the cap bolts tightened to the correct torque.
If the bearing bores or rod bores are not in specifications, they must be reconditioned. It some times will be necessary to install a new connecting rod and cap.
During assembly, make sure the cap bolts are tightened to the correct torque.