December 2000 - January 2001

Modification and Inspection:

Photos of the pistons were sent to Revmaster for inspection. The suspected "damage" was actually a hole left in the piston during the manufacturing process. An old photo confirms these holes were there prior to my having run the engine. Revmaster advises although the engine appears to be running lean there appears to be no damage.

The fuel screens and vent were checked clear and fuel flow checks close to 20 GPH.

Fuel flow through the mixture control at full rich was found to be 10.8 GPH (1/2 tank 3 point). By increasing full rich needle position (sacrificing ICO) this has been increased to 13.6 GPH.

The carb air temp probe was removed from the throat of the carb and a plug installed. The probe was then installed in the new carb air box. I felt there was a possibility its proximity to the POSA needle could affect air flow over the needle and thereby mixture.

A new O-ring was installed on the mixture control.

Cylinder heads were re-installed and valve clearances checked. Plugs cleaned and gapped.

Oil and filter changed.

The Revmaster alternate air source was replaced with a conventional carb heat system. In operation, the Revmaster system was providing only about 15 deg C rise over ambient. This would be considered insufficient for a conventional carb (which the POSA is not of course). The box and muff were fabricated from .040" aluminum. The new system should provide a much greater temperature increase. I am curious to see if the engine cools any better with the removal of the original intake. I suspect there may have been air flow from the main air inlet backwards thru the alternate filter at flight speeds. This would tend to reduce the pressure differential across the cylinders. By sealing the carb intake to the cowl this possible leak is eliminated.

I found the cabin heat nominal for our winter temps here (Translation - I was freezing my … off). To increase the heater muff output a spring was wound around the exhaust under the heater muffs for both cabin and carb heat (anyone who has ever flown here in the winter will wonder why I didn’t do this in the first place). This is a trick straight out of the Bingelis books.

Speaking of heat, it was also necessary to come up with some method to pre-heat the engine before starting up. The ductwork and heater are commonly available in most hardware stores.

The areas of the cowl which were modified to improve cooling (and clearance) were filled, primed and painted. By carefully masking the affected area and using 1000 grit wet dry sandpaper (in addition to polishing compound later) to blend the repair you can achieve good results without having to repaint the entire panel. I used a hobby shop style air brush for the colour coats and found it quite good.