ASE A1 Engine RepairEngine Block AssemblyMedium
A technician is installing connecting rod bearings. The service manual specifies a crush height for the bearings. What is the primary purpose of this crush height?
- ATo provide a sacrificial layer that wears down over time.
- BTo prevent the bearing from rotating within its housing.
- CTo allow for thermal expansion of the bearing material.
- DTo create the correct oil clearance between the bearing and the journal.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent the bearing from rotating within its housing.
Crush height, also known as 'bearing crush,' is the slight protrusion of the bearing shells above the parting line of the connecting rod or main bearing cap. When the cap is torqued, this crush ensures a tight, interference fit that prevents the bearing from spinning or walking within its housing, and also helps improve heat transfer.
Why the other options are wrong
- A. The bearing material itself provides the sacrificial layer; crush height is for retention and heat transfer.
- C. While thermal expansion is a factor in engine design, crush height's primary role is mechanical retention, not solely accommodating expansion.
- D. Oil clearance is determined by the difference between the journal diameter and the installed bearing's inside diameter, not crush height.
Bearing Crush Height
Bearing crush height is the slight amount by which a bearing shell extends above the parting line of its housing, ensuring a tight fit when bolted together.
- Prevents bearing spinning or 'walking' within the bore.
- Improves heat transfer from the bearing to the connecting rod or engine block.
- Too little crush can lead to bearing movement and failure; too much can distort the bearing.
Memory trick: Crush 'C'elebrates 'C'onnecting rod fix.