I have a very small amount if oil, a couple drops, leaking from the lower exhaust studs on two cylinders. Why?
Actually, it is logical.
8 of the 16 studs screw into inserts in the crankcase where the holes are drilled through. O-rings on the inserts keep oil away from the studs. If O-rings are bad, oil can travel up the studs and leak at the bottom of the cylinder head. Below are a couple of photos showing the result on my airplane last year.
I've attached the Rotax Service Instruction that RFSchaller referred to above. This was the solution to my leaks.
The same leak was happening at several studs. We think the reason was because the cylinder barrels had been loosened from the crankcase for a previous repair that involved removing the cylinder heads (at about 88 hours). Our theory was that the O-rings had hardened a bit in use and wouldn't completely seal when the heads were retorqued.
Actually, it is logical.
8 of the 16 studs screw into inserts in the crankcase where the holes are drilled through. O-rings on the inserts keep oil away from the studs. If O-rings are bad, oil can travel up the studs and leak at the bottom of the cylinder head. Below are a couple of photos showing the result on my airplane last year.
I've attached the Rotax Service Instruction that RFSchaller referred to above. This was the solution to my leaks.
The same leak was happening at several studs. We think the reason was because the cylinder barrels had been loosened from the crankcase for a previous repair that involved removing the cylinder heads (at about 88 hours). Our theory was that the O-rings had hardened a bit in use and wouldn't completely seal when the heads were retorqued.