ASE A1 Engine RepairCylinder Head and Valve TrainMedium
A technician is performing a valve adjustment on an overhead valve (OHV) engine with solid lifters. The service manual specifies a valve lash of 0.010 inches for the intake valves and 0.012 inches for the exhaust valves, measured with the engine cold. After adjusting the intake valve, the technician rotates the crankshaft to the next cylinder in the firing order to adjust its valves. What is the correct position for the camshaft lobe relative to the lifter when adjusting a valve?
- AThe lobe is on its opening ramp.
- BThe lobe is on its closing ramp.
- CThe lobe is at its highest point (full lift).
- DThe lobe is at its lowest point (base circle).
Show answer & explanationAnswer & explanation
Correct answer: D. The lobe is at its lowest point (base circle).
For accurate valve lash adjustment, the camshaft lobe must be on its base circle (lowest point), which means the valve is fully closed and there is no lift, allowing for proper measurement of the clearance.
Why the other options are wrong
- A. Adjusting on the opening ramp would result in an incorrect measurement, as the valve is beginning to open and lash is being taken up.
- B. Adjusting on the closing ramp would also result in an incorrect measurement, as the valve is still partially open or closing, and lash is not fully present.
- C. Adjusting at full lift would lead to an incorrect and excessively large lash measurement, as the valve is fully open.
Camshaft Base Circle
The perfectly round, concentric portion of the camshaft lobe that allows the valve to remain fully closed when the lifter is riding on it.
- Ensures the valve is fully closed.
- Used for accurate valve lash adjustment.
- Represents the lowest point of the camshaft lobe.
Memory trick: Base circle is the place, for lash to find its space.