A technician is installing a new crankshaft in an engine block. After installing the main bearings and torquing the main bearing caps, the technician attempts to rotate the crankshaft by hand and finds it binds or is very difficult to turn. Which of the following is the MOST likely cause?
- AIncorrect main bearing oil clearance (too tight).
- BOver-torqued connecting rod bolts.
- CMisaligned main bearing caps.
- DInsufficient crankshaft end play.
Show answer & explanationAnswer & explanation
Correct answer: A. Incorrect main bearing oil clearance (too tight).
If the crankshaft binds or is very difficult to turn after torquing the main bearing caps, the most likely cause is insufficient main bearing oil clearance. This means the gap between the crankshaft journals and the bearings is too small, creating excessive friction and preventing free rotation. Misaligned main bearing caps (option D) could also cause binding, but incorrect oil clearance is a more direct and common cause of this symptom.
Why the other options are wrong
- B. Over-torqued connecting rod bolts would affect the connecting rods and pistons, not the crankshaft's ability to turn in the main bearings.
- C. Misaligned main bearing caps could cause binding, as they would distort the bearing bores, leading to local areas of insufficient clearance. This is also a strong possibility but typically manifests as localized tight spots rather than overall binding.
- D. Insufficient crankshaft end play would cause resistance to axial movement, but not necessarily rotation.
Crankshaft Binding
Crankshaft binding occurs when the crankshaft cannot rotate freely due to excessive friction between its journals and the bearings, often caused by incorrect clearances or misalignment.
- Common causes include insufficient oil clearance, housing bore distortion, or foreign material.
- Requires immediate diagnosis and correction to prevent severe engine damage.
- Always check crankshaft rotation by hand after installing main caps and before connecting rods.
Memory trick: Tight clearance 'C'runch makes a 'C'rankshaft stuck.