Toobuilder
Well Known Member
I think we've all heard a tale of an airplane crashing on its first flight after a build or extensive restoration due to junk in the fuel lines. For some reason, this type of accident has always stuck with me and it guides my maintenance. Well, perhaps it's time for another reminder because I almost got bit by the same thing the other night.
Returning home from Vegas the other weekend, it was time for an oil change, so I figured as long as the engine was unbuttoned, I'd install that second P-Mag that's been on the shelf for the last year. Oil changed and Bendix magneto in the trash, the engine run showed an immediate improvement in starting and idle quality. On shutdown however, the injection servo is dripping fuel from the lower impact tube. Not good. A quick call to Don at Airflow, and the servo is boxed and on its way for overhaul. Fortunately, I have another servo attached to the RV-8 that has darkened a corner of my hangar for nearly a year. It should be noted that I have replaced every fuel line on this RV from the fuel tanks to the flow divider, and most of them are SS hard line. And while I have yet to run a drop of fuel through this "new" fuel system, I have carefully cleaned and inspected each new line as it was fabricated. I was planning on running extensive fuel flow tests prior to flight on the RV, but for this quick servo change to a flying airplane, I did not think that was required. I checked the screen in the servo and looked it over pretty well however. Servo installed and the Hiperbipe now runs better than ever! Following a thorough ground run, I flew the thing for a total of about 1.2 hours with several touch and goes, a little acro, and plenty of high power operation - all without a hint of trouble. Sunday evening was perfect for flying so I decided to take it out for a little bit before dinner. Start and runup were all normal, however as I advanced the throttle on takeoff roll, the engine fell right on its face about the time the tail came up. I pulled the power and rolled to a stop with about half the 2600 ft runway remaining.
OK, long story short: One cylinder goes cold at anything over 1200 RPM; comes back at idle. So I pulled all the injectors and did the "bottle flow test", which quickly revealed a partly plugged injector on the cold cylinder. I pulled the metering orifice out of the offending injector and sure enough, there was a tiny sliver of metal in it. Once cleaned, the injector came back to life. I figured I should take the flow divider apart and check it out too, and it had a bigger curl of metal under the lower cover. I'm guessing that this sliver of metal must have hitched a ride over from the RV and escaped my notice.
Moral of the story: Keep stuff clean and make sure you really flush all lines before you fly! Also, it may take a little time for the junk to move far enough to cause problems. I would say that you guys with brand new airplanes should not consider yourself out of the woods after your first few flights! Finally, timing is everything! Had this chunk of crud waited another 30 seconds to migrate to the injector, I may have been headline news instead of a casual forum post.
Returning home from Vegas the other weekend, it was time for an oil change, so I figured as long as the engine was unbuttoned, I'd install that second P-Mag that's been on the shelf for the last year. Oil changed and Bendix magneto in the trash, the engine run showed an immediate improvement in starting and idle quality. On shutdown however, the injection servo is dripping fuel from the lower impact tube. Not good. A quick call to Don at Airflow, and the servo is boxed and on its way for overhaul. Fortunately, I have another servo attached to the RV-8 that has darkened a corner of my hangar for nearly a year. It should be noted that I have replaced every fuel line on this RV from the fuel tanks to the flow divider, and most of them are SS hard line. And while I have yet to run a drop of fuel through this "new" fuel system, I have carefully cleaned and inspected each new line as it was fabricated. I was planning on running extensive fuel flow tests prior to flight on the RV, but for this quick servo change to a flying airplane, I did not think that was required. I checked the screen in the servo and looked it over pretty well however. Servo installed and the Hiperbipe now runs better than ever! Following a thorough ground run, I flew the thing for a total of about 1.2 hours with several touch and goes, a little acro, and plenty of high power operation - all without a hint of trouble. Sunday evening was perfect for flying so I decided to take it out for a little bit before dinner. Start and runup were all normal, however as I advanced the throttle on takeoff roll, the engine fell right on its face about the time the tail came up. I pulled the power and rolled to a stop with about half the 2600 ft runway remaining.
OK, long story short: One cylinder goes cold at anything over 1200 RPM; comes back at idle. So I pulled all the injectors and did the "bottle flow test", which quickly revealed a partly plugged injector on the cold cylinder. I pulled the metering orifice out of the offending injector and sure enough, there was a tiny sliver of metal in it. Once cleaned, the injector came back to life. I figured I should take the flow divider apart and check it out too, and it had a bigger curl of metal under the lower cover. I'm guessing that this sliver of metal must have hitched a ride over from the RV and escaped my notice.
Moral of the story: Keep stuff clean and make sure you really flush all lines before you fly! Also, it may take a little time for the junk to move far enough to cause problems. I would say that you guys with brand new airplanes should not consider yourself out of the woods after your first few flights! Finally, timing is everything! Had this chunk of crud waited another 30 seconds to migrate to the injector, I may have been headline news instead of a casual forum post.
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