Mercury D7FZ-6211-A Bearing - Connecting Rod

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Tight fitting bearings leave insufficient bearing oil clearance and will result in oil starvation. Dirt or foreign particles trapped behind a bearing insert result in high spots on the bearing, which lead to failure.

Lack of lubrication (or lubrication breakdown) has a number of interrelated causes, including excessive heat (which thins the oil), overloading (which squeezes the oil from the bearing face), and oil leakage or throw-off (from excessive bearing clearances, worn oil pump, or high engine speeds). Blocked oil passages, usually the result of misaligned oil holes in a bearing shell, will also oil starve a bearing and destroy it.

Correcting the root cause of bearing failure is crucial before reassembling the engine to prevent recurrence.

Retaining the old bearings is valuable as they may provide insights into the engine's condition.

Driving habits can have a definite effect on bearing life. Full throttle, low speed operation (lugging the engine) puts very high loads on bearings, which tends to squeeze out the oil film. These loads cause the bearings to flex, producing fine cracks in the bearing face (fatigue failure). Short trip driving leads to corrosion of bearings because insufficient engine heat is produced to drive off the condensed water and corrosive gases, which form acid and sludge that attack and corrode the bearing material.

Factors such as insufficient lubrication, the presence of dirt or foreign particles, engine overloading, and corrosion can cause bearing failure.

The old bearings should be retained for close examination as they may reveal valuable information about the condition of the engine.

When examining the bearings, remove them from the engine block, the main bearing caps, the connecting rods, and the rod caps, and lay them out on a clean surface in the same general position as their location in the engine. This will enable you to match any bearing problems with the corresponding crankshaft journal.