ASE A1 Engine RepairEngine Block AssemblyMedium
A technician is inspecting a crankshaft. The service manual specifies a maximum runout of 0.002 inches (0.05 mm) for the main bearing journals. The technician measures the runout on a journal as 0.0035 inches (0.089 mm). What is the MOST appropriate action?
- AInstall new main bearings with the crankshaft.
- BMachine the crankshaft journals to reduce runout.
- CReplace the crankshaft.
- DInstall shims under the main bearings.
Show answer & explanationAnswer & explanation
Correct answer: C. Replace the crankshaft.
Crankshaft runout exceeding specifications indicates a bent crankshaft, which cannot be repaired by machining or shimming and requires replacement to ensure proper engine operation and longevity.
Why the other options are wrong
- A. New bearings will not correct excessive crankshaft runout; they will wear prematurely.
- B. Machining reduces journal diameter, but does not correct a bent crankshaft causing runout.
- D. Shims are not used to correct crankshaft runout; they are sometimes used for bearing clearance adjustments, but not in this context.
Crankshaft Runout
Crankshaft runout is the amount of wobble or deviation from true rotation of the main bearing journals, indicating a bent shaft.
- Measured with a dial indicator on main bearing journals.
- Exceeding specifications often requires crankshaft replacement.
- Can lead to excessive bearing wear and engine vibration.
Memory trick: Runout too high, a new shaft you must buy.