Precision Measurement Supply - Fixtures, Tooling And Measuring Devices For Professional Engine Builders

Differential Pressure Cylinder Tester
Operating Instructions

  1. Remove all spark plugs, air cleaner, radiator cap and oil filler cap.

  2. Rotate the piston of the cylinder being tested to the TDC position on the compression stroke (make sure both valves are closed).

  3. Connect line from air compressor to quick-disconnect coupling on the side of the regulator.  Caution:  DO NOT connect compressor to ship hose.  Be sure line pressure on compressor doesn’t exceed 300 psi.

  4. Insert spark plug adaptor into the quick-disconnect coupling located on the end of the whip hose of the regulator.  Note:  The spark plug adaptor is not yet placed in the spark plug hole of the cylinder head.

  5. With the spark plug adaptor connected to the whip hose, air should now be flowing through the regulator.  Adjust the INPUT pressure on the regulator (left-hand gauge) to any of the input pressures covered on the comparison chart (70, 80, 90, or 100 psi).  Note:  You should use an input pressure that is AT LEAST 10 psi less than the pressure on your compressor.   EXAMPLE:  If your compressor will only hold a pressure of 90 psi, then set the input pressure on your left-hand gauge at 80 psi.  It is important that you maintain the same exact input pressure reading on all cylinders tested.

  6. Remove spark plug adaptor from whip hose of regulator and install it into the cylinder to be tested.  Note:  With the adaptor removed from the whip, the input pressure may or may not remain where you set it – this is normal because the regulator only functions properly with air flow.

  7. Connect the whip hose to the spark plug adaptor that is now in the spark plug hole.

  8. Make the necessary adjustments to the regulator to maintain the proper input pressure (left-hand gauge).

  9. The RELATIVE PRESSURE of the cylinder being tested is automatically indicated on the right-hand gauge.  EXAMPLE:  If you are using 80 psi input pressure and your right-hand gauge reads 74.4 psi, by checking the comparison chart, you will find that you have a 7% leakage.

  10. Record leakage and repeat test on remaining cylinders.

Evaluating Results: Due to running clearances and normal wear, you can’t expect a cylinder to have zero leakage. However, all cylinders should read within a few percentages of one another. A difference of 5 or 6 psi between cylinders is okay, but if you get out to 10 or more psi difference between cylinders, you should find out what is causing the problem and correct it. 

Listen For Escaping Air: Air escaping from the crankcase or breather is an indication of leakage past the rings. Air escaping out of headers indicates a defective exhaust valve or seat. Air escaping from carburetor or intake manifold indicates a defective intake valve or seat. If air bubbles are present in the radiator or coolant, check for a leaking head gasket or a cracked head or block. 

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