BillC Posted August 20, 2014 Report Posted August 20, 2014 Hi all, I've been getting a thin black streak along the left side of my '79 201 starting at the left cowl flap hinge line. The streak goes back to the midpoint of the pilots window on the side of the fuselage. I added some illuminating dye to the oil and used a UV Black flashlight to show where the "oil"(?) was coming from. After an hours flight I checked the engine for a telltale sign. There were NO oil leaks. The odd thing is that the streak itself does NOT illuminate. Therefore it cannot be from engine or prop oil. I'm thinking that the cowl flap hinge may be 'working' and leaving the black streak. The streak does not smell like oil. My oil was just changed and is very clean so something else is causing this black streak. I washed the engine and inside of the cowl very well before troubleshooting this problem so it's not from previously spilled oil either. Has anyone else had this problem and did you figure out what it was? Thanks, Bill
Andy95W Posted August 21, 2014 Report Posted August 21, 2014 Similar to a smoking rivet (or fretting corrosion). As the metals in the hinge wear, the metal erodes into aluminum dust which is then carried with the slipstream by the lubricating oil from the hinge. Over time, the wear isn't just caused by using the cowl flaps, but by the vibration that is now taking place between the worn parts. I'll bet it happens even more after flying through rain. Not a real cause for concern, but you should probably assume you'll need the hinge repaired/replaced in time. Possibly sometime in the next 5 years/thousand hours or so? In the meantime you'll just have to keep wiping up the residue. 1
Hank Posted August 21, 2014 Report Posted August 21, 2014 Happened to me on the left side. The cowl was rubbing and some Teflon tape made it quit.
BillC Posted August 21, 2014 Author Report Posted August 21, 2014 Thanks guys. Co2, I'll give it a good inspection tomorrow. Thank. Jim, I haven't flown in the rain since this started. Good idea about the teflon tape, Hank. I'm due for some new tape. Good explanation Andy. That makes perfect sense. It breaks my heart to see my polished baby with a streak. I'll be ordering a new hinge tomorrow. Thanks again, Bill
jlunseth Posted August 21, 2014 Report Posted August 21, 2014 It even has a name, "chafe leak." They are common. A little Simple Green Extreme on a cloth will wipe it off.
N201MKTurbo Posted August 21, 2014 Report Posted August 21, 2014 Wow I wish my plane only had one streak. How do you do it? 2
jlunseth Posted August 21, 2014 Report Posted August 21, 2014 Plexus works well, too. Or just the cloth, but that usually leaves a smudge.
BillC Posted January 23, 2015 Author Report Posted January 23, 2015 Sorry for not following up on my mysterious "oil" streak. After adding the oil dye and using a strong black light I found the streak on the left side of the fuselage, beginning at the left cowl flap, was not oil from a leaking engine. Since the 'oil' did not illuminate under the black light, I examined further and found it was the left cowl flap chaffing at the two bolt hinges. Apparently the black dust from the 'working' flap aluminum was making black dust and adhering to the oil vapor and making it's way out along the bottom cowl onto the left side fuselage. I removed the flap, installed clear teflon tape to the rubbing parts of the flap and installed new hardware. The streak is gone! Easy fix that may help others get rid of that fuselage streak. Perhaps M20J has the same problem as I with the streak on the left side of the fuselage. Andy hit it right on the head. Thanks. 2
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