ASE A1 Engine RepairCylinder Head and Valve TrainMedium
A technician is performing a visual inspection of a camshaft with a dial indicator. The maximum lift measured on an intake lobe is 0.250 inches, and the base circle runout is within specifications. The service manual specifies an intake valve lift of 0.400 inches. What is the most likely cause for the discrepancy in measured lift?
- AThe dial indicator is faulty.
- BThe camshaft lobe is excessively worn.
- CThe valve spring is weak.
- DThe rocker arm ratio is incorrect.
Show answer & explanationAnswer & explanation
Correct answer: B. The camshaft lobe is excessively worn.
A significant reduction in camshaft lobe lift (0.250 inches measured vs. 0.400 inches specified) with a normal base circle runout strongly indicates that the camshaft lobe itself is excessively worn. This directly reduces the amount the valve is lifted.
Why the other options are wrong
- A. While a faulty dial indicator is possible, the question implies a valid measurement. If it were faulty, it would likely show inconsistent readings or obvious errors.
- C. A weak valve spring would cause valve float at higher RPMs but would not directly reduce the maximum lift provided by the camshaft lobe.
- D. An incorrect rocker arm ratio would cause a consistent, but different, lift from specification, not a drastic reduction from a specified camshaft lift (which is typically measured at the lifter or cam). If 0.400 is specified at the valve, and 0.250 is measured at the cam, the cam itself is worn.
Camshaft Lobe Wear
The deterioration of the camshaft lobe profile, typically leading to a reduction in valve lift and duration.
- Reduces valve lift and duration.
- Causes loss of engine power.
- Can result in rough idle and misfires.
Memory trick: Low lift, worn-out shaft.