Crankcase leak test for paramotors

by Had Robinson

Leaking main engine seals are rare. However, leaks in the main seals, particularly, will make the engine harder to start and can lean it out at the high end.  Just the same, 2 stroke engines are messy and there will always be some oil and gunk on the engine.  It must not be excessive where it drips while running.

This method uses a soap solution to test for leaks.  If the flywheel has not been removed, that part of the engine may need to be submerged in water.  The same would apply to the drive side main seal if it has a clutch that has not been removed.  Because the engine will be internally pressurized, we do not need to be concerned about water entering any part of the engine.  The only part of the engine that does not need to be submerged or tested for leaks is the exhaust port.  If water gets into the reed valve opening, it is of no concern because it will not get any further than the valve.

Remove the engine from the frame and then remove the exhaust system, spark plug, cooling shroud (if present), carburetor, and redrive (if present).

Top 80 ONLY  This step is suggested for the Top 80 and any other motors which have an internal crankcase port that is used to power the fuel pump.  Remove the carburetor and ROTATE the gasket between the carburetor and reed valve 180 degrees.  Reattach the carburetor.  This will block the port going into the carburetor and prevent possible damage to the fuel pump diaphragm in case the crankcase becomes over pressurized.  If you are very careful and are certain you will not over-pressurize the crankcase, this step may be skipped.

The engine can be pressurized through the spark plug opening (Top 80) or through the crankcase pulse port used to power the fuel pump.  For the Top 80 (and any other motor which does not have an external pulse port), use the fitting of an engine compression test tool.  Most of them have a check valve to hold the compression test value so it can be read.  It might take a little ingenuity to fit it all together so that it works for you.

The best way to pressurize the crankcase is through an external pulse port (see photo below).

testing a paramotor crankcase for leaks

Use leak detector solution (or a liquid soap solution) and apply it all around the main seals (black arrow in photo) and, if desired, around the reed valve body and where the cylinder attaches to the crankcase.  This engine had 100's of hours on it and the main seals were still good.

Pressurize the crankcase to about 3 psi.  Any leak of the seals will be immediately seen.

If you cannot access the main seals, you will have to partially submerge the engine in water (while maintaining crankcase pressure) and look for bubbles.  If you do not or cannot maintain crankcase pressure when partially submerging the engine in water, there is a good chance water will enter the engine!  Water will not harm a coil in good condition.  However, keep as much of the secondary wire as you can and the spark plug cap out of the water.  You do not want any water in the spark plug cap.

Replace any seals or gaskets that leak.  Reassemble the engine.

Note:  When replacing the cooling shroud on a Top 80, put copious amounts of RTV between the large washers on the cylinder head studs and shroud.  This will help cut down the wear of the shroud at these points due to severe engine vibration.

Turkey Vulture