ASE A1 Engine RepairCylinder Head and Valve TrainHard
A technician is inspecting the camshaft lobes of an engine that exhibits a consistent misfire on one cylinder. Using a dial indicator, the technician measures the lift of the affected intake lobe and finds it to be significantly less than the specified value. The corresponding exhaust lobe's lift is within specification. What is the most likely cause of this specific issue?
- AWorn camshaft bearing.
- BCollapsed hydraulic lifter on the exhaust valve.
- CWorn intake rocker arm.
- DWorn intake camshaft lobe.
Show answer & explanationAnswer & explanation
Correct answer: D. Worn intake camshaft lobe.
A significantly reduced lift on a specific intake camshaft lobe, while the exhaust lobe is fine, directly indicates wear on that particular intake camshaft lobe. This wear would prevent the valve from opening fully, causing a misfire.
Why the other options are wrong
- A. A worn camshaft bearing would typically affect the entire camshaft's rotation or multiple lobes, not just a single intake lobe specifically.
- B. A collapsed hydraulic lifter on the exhaust valve would affect exhaust valve lift, not intake valve lift.
- C. A worn intake rocker arm could reduce valve lift, but the primary cause of reduced *lobe* lift is wear on the camshaft lobe itself. If the rocker arm was worn, the lobe lift would still be correct, but the valve lift would be reduced.
Worn Camshaft Lobe (Reduced Lift)
Excessive wear on a specific camshaft lobe, resulting in reduced valve lift and duration, leading to poor cylinder breathing and a misfire.
- Causes reduced valve lift.
- Leads to engine misfire, rough idle, reduced power.
- Diagnosed by measuring lobe lift with a dial indicator.
- Requires camshaft replacement.
Memory trick: Low lift on one lobe, cam's worn, it's known.