VII. Electric Testing
The primary reason for electric testing any spark plug is to determine if the ceramic insulator is dielectrically sound, i.e.,
there are no hidden fractures or pin holes through which the applied high tension ignition voltages could be diverted to
ground instead of firing the plug.
The above electric testing of spark plugs can be accomplished by using the indicator portion of the Model AV11-1 Spark
Plug Cleaner and Indicator Unit as follows: See Section III, Page No. 10 for Unit Installation and Cleaner Operation.
Operation
NOTE
The indicator will provide a quick and accurate dielectric soundness check of aircraft plug
insulator with exception of firing end and approximately 1/8" of sleeve end. These areas should
be carefully inspected for chips and cracks with an AV24-1 Magnifying Inspection Light.
1. Select a pair of Indicator Adapters corresponding to the thread size of spark plugs to be tested - 14 MM to 18
MM. Use a 7/8" spark plug gasket under each adapter and moderately tighten into test chambers.
2. Screw aircraft spark plugs, one into each chamber, without any seat gaskets, full length of threads, finger tight
only. Slight air leakage is necessary to maintain best sparking ability of plugs.
NOTE
Plugs must be clean and properly gapped to engine manufacturer's specifications. Spark plug.
gap sizes should not exceed .025 for satisfactory test results.
3. When checking shielded type aircraft spark plugs, insert correct type terminal contactor into the ceramic
shielding barrel of each plug.
A. Type CL-235 Short Contactors are for low altitude type spark plugs with 5/8 - 24 threaded shields.
B. Type CL-238 Long Contactors are for high altitude type spark plugs with 3/4 - 20 threaded shields.
4. Place H.T. voltage contact arm onto the exposed end of terminal contactor in one plug.
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