Subtopic: Selection, operation, maintenance and repair of I.C. engines
Question Statement:
During a routine maintenance diagnostic compression test on a tractor engine, a cylinder shows low compression pressure. A small quantity of heavy engine oil is squirted through the injector hole into the cylinder (wet test), and the compression gauge reading increases substantially. This diagnostic result indicates:
Options:
(A) Leaking cylinder head gasket
(B) Worn or stuck piston rings / worn cylinder wall
(C) Burned exhaust valve seat
(D) Cracked cylinder head
Answer Key:
B
Step-by-Step Solution & Explanation
- **Wet Compression Test Principle:**
- Heavy engine oil momentarily coats and seals the clearance gap around worn piston rings and the cylinder liner bore.
- If compression pressure increases significantly after adding oil, the loss of compression is confirmed to be due to **worn piston rings or worn cylinder bore**.
- If compression remains unchanged, the leakage is through valves or a blown head gasket.