Problems, Problems, Problems...

I haven’t blogged for a while due to a combination of things; and one of those has been continuing mechanical problems with the Cheetah. For a few weeks, I had thought we were catching up with her and then I made the “mistake” of trying to get ahead of the performance curve by adding a PowerFlow exhaust to the engine. That was when all hell broke loose, some of which had nothing to do with the PowerFlow and the other part of which we’re trying to understand and figure out whether the PF had anything to do with it.

The major bugaboo has been the right fuel tank leak that developed. I caught it during a preflight month’s ago. The Cheetah, like all Grumman singles, has a wet wing that contains gas by using a sealant. Sometime in a Grumman’s life, you can expect the tank to start leaking and the sealant to need replacing. Well, this became our time, though the presence of two spatulas left in from previous attempts and now retrieved from our wing indicates that the airplane has suffered from this problem before. (The logs are down at my mechanic’s shop so I can’t check them to see when this was a previous problem.) Bill’s on his fifth attempt to solve the problem, though to his credit he’s only charging us for one. His son-in-law, Robby, an Aircraft Inspector, indicated to me that this kind of trail and error was par-for-the-course when repairing fuel tank leaks. A Traveler owner down at Galveston just dealt with the same problem, though he managed to get his fixed on the fourth attempt. It’s frustrating ordeal for all of us, me because of the months of flying time I’m losing and Bill because of the money he’s losing. We believe we have it fixed wth this fifth attempt. I hope so. I just topped that tank of and with av-gas over $5 per gallon, it’s going to be an expensive test if we’re wrong.
I wish that was all that has been going on, but it’s not. Two things manifested itself with the installation of the PowerFlow exhaust system. Both mags began “popping” during the mag checks, and the left mag will often “surge” (drop 300-400 rpm and then recover and repeat it again) when the engine is run on the left mag alone. At first we thought it was a common heat-related failure induced the mag, but we saw it with a cold engine after changing out to a “new” mag. We have checked the switch, the wires, and the plugs using testers and can’t find a problem. Bill and I are both suspicious of the ignition switch, but there is also the possibility that the PF has uncorked a more serious problem with the engine.

Secondly, for the one or two short flights I have been able to make after we installed the PowerFlow, the engine oil temperatures have shot up to the high side of the green. It looks like this was induced by the PF system, and there was an article in the AYA Star (the Grumman owner’ group newsletter) that unfortunately appeared after I had installed the PF and discussed just a such an induced problem with the system in Tigers. Right now, though, with the mag drop problem we’re experiencing, I can’t say anything for sure about the cause. Once we get the engine operating correctly, then I’ll take a look at the oil temp and decide where to go from here. The article suggested opening more exit area at the bottom of the cowling, something I would do only after reworking my baffles and resealing every air escape hole in the top of the cowling I can find.