Wednesday, August 13, 2008
Lesson from Tandy
This afternoon after I got the Bomber and the Airborn cleaned up from flight testing, I unbolted the SuperTiger G21/35 from the Fubar 600X airframe and removed the crankcase pressure line. While this line into the tank was not completely stopped up, it had a thick sticky residue on the inside. So I hooked up a line from the engine's crankcase pressure fitting and ran it into a bowl of water as shown below. With the glow plug removed, I spun the prop, but there were no bubbles produced in the water. This indicated that the pressure fitting screwed into the upper left corner of the back plate was stopped up.
I removed the pressure fitting from the back of the engine and found it was completely clogged up with a dark brown "grunt" that looked a lot like hardened varnish. Hanging dormant for four years had allowed the small .018" hole in the fitting to become sealed over. After soaking the pressure fitting in Acetone for about an hour, I used a .018" drill bit and reamed out the hole in the pressure fitting as shown below. Then I cleaned up the pressure fitting inside and out.
I screwed the pressure fitting into the upper left corner of the back plate and reinstalled the engine in the Fubar airframe. I filled the fuel tank with alcohol and put on the prop, but left the glow plug out. I put a black tubing extension on the fuel line and ran the end into a bowl as shown below. I spun the prop and the crankcase pressure pumped the tank completely dry! Wa-La, the problem is now fixed.
The lesson learned in this exercise is that if you let an engine set unrun over a long period of time (years), you need to clean out the small .018" hole in the pressure fitting before you try to run it again. Now I need to go back out to the field soon and test fly the Fubar 600X. I also need to practice the climb out on both the Airborn and the little Bomber until I can keep them in the groove up to the 35 second engine cut off time and also work on my transition..........................Tandy