Rotax 503 Exhaust Gasket Leak

I’ve been chasing a messy issue on my Titan Tornado. Every time I fly I end up with sticky black oil on the tail of the airplane. The black goo is all over the engine and it is difficult to tell where it’s actually coming from. I finally decided to remove the engine and address the problem. I was convinced that a tear down was in order to replace the main seals on the crankshaft, but it turns out the problem was much easier to fix.

As you can see above, the goo was leaking out all over the exhaust side of the engine. It was also all over the rear cylinder head and cooling shroud. Where ever it was originating it was getting into the shroud and being blown everywhere.

Once I removed the exhaust manifold the issue was clear. If you look at the front exhaust flange area on the left cylinder you will notice that there is oil above the exhaust port where the gasket was. The only way for oil to get there is if the gasket was not sealing. I did notice when I removed the exhaust manifold that the bolts on that cylinder were not tight. I cleaned everything up using mineral spirits which worked great. Then, I ran a file over the mating flange on the exhaust manifold and found it was not even close to flat. After 15 minutes of filing I smoothed the surface with 220 grit paper on a piece of plate glass to get a flat surface. To remount the manifold I first loosened the cylinder/head bolts on both cylinders. Then I mounted the manifold and tightened it down. Finally I re-torqued the head bolts. This should give a good seal and keep the airplane clean. I used Locktite on the exhaust manifold bolts to help keep them in place. Now I’ll have to see how this holds up. I’ll update this as time goes on.