Cylinder Leakage Test

Tools Required

J 35667-A  Cylinder Head Leakdown Tester

With the use of air pressure, a cylinder leakage test will aid in the diagnosis. The cylinder leakage test may be used in conjunction with the engine compression test, to isolate the cause of leaking cylinders.

CAUTION: Refer to Battery Disconnect Caution .
1. Remove the battery ground - negative cable.
2. Remove the spark plugs. Refer to Spark Plug Replacement in Engine Controls.
3. Install the J 35667-A  .
Fig 1: Measuring Cylinder Leakage
Courtesy of GENERAL MOTORS CORP.
4. Measure each cylinder on the compression stroke, with both valves closed.
IMPORTANT: It may be necessary to hold the crankshaft balancer bolt, to prevent piston movement.
5. Apply air pressure, using the J 35667-A  . Refer to the manufacturer's instructions.
6. Record the cylinder leakage readings for each cylinder.
IMPORTANT:
• Normal cylinder leakage is from 12-18 percent.
• Make a note of any cylinder with more leakage than the other cylinders.
• Any cylinder with 30 percent leakage or more requires service.
7. Inspect the four primary areas, to properly diagnose a leaking cylinder.
8. If air is heard from the intake or exhaust system, perform the following procedure:
   • Remove the valve rocker arm cover of the suspect cylinder head.
     • Ensure that both valves are closed.
     • Inspect the cylinder head for a broken valve spring.
   • Remove the suspect cylinder head and inspect. Refer to Cylinder Head Cleaning and Inspection  .
9. If air is heard from the crankcase system at the crankcase, oil filler tube, perform the following procedure:
   • Remove the piston from the suspect cylinder.
   • Inspect the piston and connecting rod assembly. Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection  .
   • Inspect the engine block. Refer to Engine Block Cleaning and Inspection  .
10. If bubbles are found in the radiator, perform the following procedure:
    • Remove both cylinder heads and inspect. Refer to Cylinder Head Cleaning and Inspection  .
    • Inspect the engine block. Refer to Engine Block Cleaning and Inspection  .
11. Remove the J 35667-A  .
12. Install the spark plugs. Refer to Spark Plug Replacement in Engine Controls.
13. Install the battery ground - negative cable.