One of the things that came out of the OMC paper
   was how they suggested checking the condition
   of the engine. They recommended the aircraft engine
   static air leak check where regulated air is introduced
   into the combustion chamber through the spark plug
   hole with the rotor in top dead center. The rate of air
   leakage is measured as a pressure drop across a fixed orifice
   in the pressure line. This will be very familiar to all you
   A & P's out there. You can buy the necessary equipment
   off the shelf from the aviation suppliers at relatively
   low cost. I have one I bought to check my O-470. You need
   to lock down the engine so it cannot rotate. Be careful
   doing this with a prop installed as being hit by the prop
   as it comes around under the influence of air pressure
   and a failed lock down can really hurt you.

   The static air leak test is applied to all three rotor faces.
   If two of the three readings indicate high leakage an apex
   seal is bad. If only one reading indicates excessive leakage
   a side seal is bad.

   Mazda recommends recording the pressure as you rotate the
   engine. This requires rather expensive Mazda test equipment and
   the numbers depends on the speed of engine rotation.

   Taking the Shrader valve out of a standard compression
   tester is hit or miss and does not give a good indication
   of side seal functioning.
   --
   Paul Lamar ...No rotor no motor.

Here is a possible method for checking any other seal leaks. When I was
designing calipers for a company that I worked for we used to check
bleeder screws on the calipers we assembled to make sure they were ok to
ship. We put pressurized helium into the fluid port and had a sniffer
that made an annoying noise when it smelled leaks. It was nice to
because it was a variable sound based of leak amount. You can do this
with any gas sniffer out there. Not so useful for compression checks but
a decent way to see if your housing seals are going bad.

Rob Woods


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