First of all, thanks to the many people who responded to Buly's message. I'm sorry I wasn't able to call everyone back. I was on the phone for a couple of hours with various helpers, but failed to explain to all of them that I was an idiot. In my own defense it had been a very long day.
With regard to mogas, epoxy tanks and filters, let me try to clear up any misunderstandings and provide whatever information I can to assist others avoid the same issues....
Yes. My MGS 335 built tanks failed to hold up to ethanol in mogas. The symptoms of failure are (or were in my
case) fairly benign. After about 4 years there was evidence of softening of the inner strake skin. This first showed up as faint lines along the curve of the strakes where we bend the skin. There were no leaks or "gummy stuff" found in the fuel or filters. At about 5 years, reaching through the filler holes to squeeze the inner skin proved that the
inner skin has significantly softened. I decided tht the tanks needed to be rebuilt. I removed the strake tops and discovered that the entire inner skin was soft. Interestingly, in the areas where there were 2 BID tapes the tapes were soft, but the skin under them was undamaged - it seemed to me that the ethanol had weakened the skin very gradually, and had just about got through two layers. A leak was clearly imminent.
To cut a long story short, I removed the bulkheads and removed the inner skin down to foam. I then rebuilt the strakes from the inside with plans layups using EZ-poxy and built and installed new bulkheads. When this was all cured I constructed inner tanks in each of the three sections of each strake using vinyl ester resin and 1 UNI. These inner tanks have lids which were added to the underside of the strake tops prior to re installation. Perhaps the inner tanks may be superfluous based on others experience with EX-Poxy (Perry
Mick, for example). I just didn't want to do this (roughly 80 hrs) job again so a I used a "belt and braces" approach.
The strake "lids" were reinstalled and taped. Last week I completed the refinishing of the strake tops filled the tanks, taxi tested, and cleaned the filters. There was very little crud in the filters. I then test flew the airplane for 1.5 hrs and cleaned the filters again prior to my planned cross country flight from Rhode Island to Florida. I made a fuel stop for mogas at SFQ in VA, then topped up again at BNL in SC. On my first use of the right tank after the BNL fillup The engine immediately ran rough at reduced rpm. Switching off the right tank did not rectify the situation. (each tank has a separate pump & filter. The feed is T'd at the rail and I always switch both on, then switch off the one I'm moving from). This means that the engine was never running on just right tank. Theoretically it should have been getting
fuel from the left. Apparently it was not.
The engine ran rough at around 3500 rpm max throttle from then until touchdown at 17FL. Switching fuel pumps and injectors had no effect. I'll cover the emergency landing in another post. After landing I turned to back-taxi on the 7500' runway and found that the engine ran perfectly. I suspected filter blockage, but was puzzled as to why running on left tank did not solve the problem. On inspecting the filters I found the left one to be clean, and the right one completely blocked with about a cubic MM of epoxy dust material. Failure of the engine to start after filer cleaning was simply my error in forgetting to switch the manual tank isolation valve. Once I switched this valve the engine started and ran as normal on the last leg from 17FL to LNA.
My guess is that the pressure surge from initializing the right pump cause some epoxy dust to be forced through the (post pump) Earls stainless filter
and on to the injectors' screens. This is the only way that the left pump would have failed to correct the problem. As for the sudden "arrival" of the crud after finding clean filters twice - Here's my theory, for what it's worth - When at the hangar I fill the tanks from 5 gal fuel containers. At SFQ and BNL I used the airport pumps. These pumps are VERY high volume / high pressure. You can fill a Cozy tank in just a few seconds. I think that the high volume fuel insertion caused turbulence in the tanks that hadn't occurred with my normal filling method, and forced crud out of the corners into the sumps.
Anyway, thanks for all the good wishes. I'm safe & sound back in South Florida, and apart from this inconvenient little incident, the engine purred like a kitten the entire way.
John Slade
Turbo Rotary Cozy N96PM
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