++safety Alert++

FMild · #1 10-26-13, 01:41 PM

Jim,
I'm by no means an expert but I've learned alot about my "D" model (non-turbo'ed) in the last two years with malfunctions due to the a/c sitting awhile. The most relevant one to your situation was after doing some work with the fuel selectors moved to "Off" I couldn't get the front engine to start. I'd prime it & it would pull away from the starter but then die. Turns out the fuel selector didn't make it all the way from "Off" to "Left." The little ball/spring deal which gives the feedback of the detent was gummed up and I truly wasn't getting it into the detent. They need to be lubed well & watch for track wear on the plate if they're not which will cause more problems.
That being said if you didn't move it at all then the only apparent culprit is the valve itself. I understand from the manual that you have an extra return line to the sump but that wouldn't cause it all to burn from one tank. I would suspect you have an internal failure in the valve itself which allowed the valve to port fuel to the front engine. I'm interested to see what you find.

B2C2 · #2 10-26-13, 02:32 PM

Having studied the fuel system in the parts manual, I would have to agree with that. The only path I can see for the fuel to be cross fed is via the valve assembly. I am not familiar with the internal construction of the valve. I looked around on the web and couldn't find an exploded view of the internals, so I can't suggest a specific mechanism, but it seems like something has to be broken inside the valve assembly causing fuel to be drawn from the opposite tank for this to happen.

Jim Smith · #3 10-27-13, 10:22 AM

Ed, I did actually think "wow is this situation so unique I've stumped everybody or no one else has ever had this occur!"

I've come to the initial conclusion that the only way this can occur is through a fuel valve. However, with the balls in the valves being spring loaded and the plane stationary when the problem materialized, I just can't see how they could fail in such a manner that would cause a complete change in fuel flow. Maybe a little leakage one way or the other but not a complete change. I exercised the valves through all of their positions when I checked for proper positioning and detents, and will do my one hour test flight this week and report back to everyone if the problem persists or has 'corrected' itself. Quite frankly, I sure hope it hasn't 'corrected' itself without me taking any corrective action.

hharney · #4 10-27-13, 08:22 PM

Jim
Just be careful as you do your flight test. Be sure to only make one engine/fuel change at a time, keeping power to one engine without changing both.

A fatal Skymaster accident earlier this year was a test flight just after having worked on the fuel system. Just be careful.....

Jim Smith · #5 10-28-13, 03:19 PM

Going to be just running on the mains and then see if I had greater fuel burn out of one side, and none out of the other, as occurred on the last flight. Thanks for the concern. I'll be staying very close to the airport!

Jim Smith · #6 10-29-13, 08:22 PM

Hey guys. Flew today and burned 15 gallons. Both sides took an almost equal amount upon refueling. Not sure if exercising the valves corrected the problem or this condition only occurs after burning more than 50 gallons. The problem occurred after 50 gallons used (67 total). I rarely go that high without refueling. I'll continue flying and be watching the fuel gauges for uneven burn and topping off after each flight. I'll keep everyone advised.

Jim Smith · #7 10-31-13, 04:24 PM

After analyzing of the conditions and circumstances, discussions with several fine mechanics and Skymaster specialists including Owen Bell and Don Neiser, we've all come to the conclusion the only way this could've occurred is through one of the fuel valves. How, we're not exactly sure. Possible trash, weak spring(s), bad o-ring(s), or internal corrosion. My valves look beautiful on the outside but are original and have never been rebuilt so who knows what the insides look like. There is the possibility that one valve was slightly out of detent but it would've been only ever so slight. My future course of action and recommendation to other owners is, during your preflight make sure you hear each valve click as you put it into position, if it had been previously moved out of position from the mains. The cables from the valve selector handles to the valves do tend to get some slack and play. Adjust if necessary. Additionally, even though I'm not aware of any Cessna SID or an AD, it would be prudent to remove your valves and go through and rebuild them if they've never been rebuilt. At the very least inspect them internally. Being a 1969, mine are 44 years old and I'd have to imagine there may be some stuff going on in there that probably isn't good especially where there's any rubber concerned. You can maintain your aircraft in tip-top condition and one thing like this, that isn't required to be rebuilt unless it's broken, can take you down. There have been too many Skymaster crashes attributed to fuel exhaustion and who knows if this could be part of the reason why. Also, if you have a fuel flow/totalizer system, these add a great level of confidence with fuel usage, but continue monitoring for uneven burning from your good old fuel gauges. Thanks to everyone for your input.