Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsStarting System Diagnosis and RepairHard
A technician is checking the starter motor's pinion gear and flywheel ring gear for engagement. What is the typical clearance between the pinion gear and the flywheel ring gear when the pinion is fully engaged?
- A0.200 - 0.300 inches (5.00 - 7.60 mm)
- B0.100 - 0.150 inches (2.50 - 3.80 mm)
- C0.010 - 0.020 inches (0.25 - 0.50 mm)
- D0.040 - 0.080 inches (1.00 - 2.00 mm)
Show answer & explanationAnswer & explanation
Correct answer: C. 0.010 - 0.020 inches (0.25 - 0.50 mm)
The clearance between the pinion gear and the flywheel ring gear (often called pinion-to-ring gear clearance or overrunning clutch clearance) is critical for proper engagement and disengagement. The typical specification is a small gap, usually around 0.010 - 0.020 inches (0.25 - 0.50 mm). This allows for proper mesh without binding.
Why the other options are wrong
- A. This clearance is far too large and would result in the pinion not engaging the flywheel at all, or only barely touching.
- B. This clearance is excessively large and would prevent proper engagement, causing grinding or no-start conditions.
- D. This clearance is too large and would likely lead to incomplete engagement, grinding, or improper cranking.
Pinion-to-Ring Gear Clearance
The small gap maintained between the starter pinion gear and the flywheel ring gear when fully engaged, crucial for proper operation.
- Ensures smooth engagement and disengagement.
- Prevents binding and excessive wear.
- Typically measured in thousandths of an inch or fractions of a millimeter.
Memory trick: Small gap for gear mesh, keeps the starter fresh.