Compression & Cylinder Leakage Testing

Name ______

Compression & Cylinder Leakage Testing Lab #4

Calculate the displacement of the engine that the compression test was performed on in lab:

Compression Testing

The compression tester measures pressure by trapping the cylinder pressure by means of a check valve and indicating the pressure trapped above the check valve on the pressure gauge. The instrument is connected to the cylinder by removing a spark plug and using a compression adapter hose which is threaded in the spark plug hole. Compression tests may be made to determine whether or not the cylinder can compress an air-fuel mixture to a suitable pressure for efficient combustion.

Results:

Compression Ratio: ______

Cylinder 1: ______Cylinder 2: ______Cylinder 3: ______

Cylinder 7: ______Cylinder 8: ______

Questions:

1. What do the test results indicate concerning the condition of the engine?

2. Why is uneven cylinder pressure objectionable?

3. Why should the engine be brought to operating temperature?

4. What are possible causes of low compression? a. – b. – c. – d. – 5. Would you recommend an engine overhaul for this engine based on this one test? Why or why not?

1 Cylinder Leakage Testing

In the modern engine improved designs and higher compression ratios are providing greater power performance and economy, but the valves, rings and cylinder heads are being subjected to greater combustion pressures than ever before. These advances in engine design have increased the need for better and more accurate means of testing cylinder leakage. The cylinder leakage test will point out exhaust and intake valve leaks; leaks between cylinders or into the water jacket, or other causes of compression loss. The tester applies air to the cylinder at controlled volume and pressure and measures the percentage of air leakage. Even the smallest cylinder leak can be easily detected. In many cases unsatisfactory performance and rough idle are caused by combustion chamber leakage. Experience and research have established that a compression test alone may not show up this fault. It is normal for a small amount of air to escape past the rings into the crankcase. However, any leakage through an intake valve, an exhaust valve, head gasket block or excessive leakage past the rings indicates trouble which must be corrected before satisfactory engine performance can be expected.

Results:

Compression Ratio: ______

Questions:

1. Cylinder leakage on an engine in good condition should not exceed ______%

2. What test results would show the following:

a. Engine is in good condition?

b. Engine is in need of a rebuild/replacement?

3. Explain the following results: a. Air escaping through the carburetor

b. Air escaping through the exhaust pipe

c. High percentage of leakage through adjacent cylinders

d. Air escaping through the radiator

e. High percentage of leakage through the crankcase 4. How would you determine if the leakage was due to stuck rings?

2 5. Explain the purpose of this test and what can be determined about the condition of the engine by its use.