Minor Oil Leak - Opportunity for P.M.

687.8 hours

Over the last couple of flights I've noticed a slight amount of oil was being blown around the cowling and I've cleaned it up and let it leak again to determine the source.  My worry was that it was the Lycoming 13792 Crankshaft Oil Seal (AEL13792 from ECI) on the front of the engine.  Having replaced one of those before on a different plane, I wasn't looking forward to it.  I prepped myself for the repair and got a couple of seals, and also bought the PlioBond #20 (8 oz. can) that is required to get it back in and sealed.  The only thing I didn't have was the ST-383 tool that is recommended by this Procedure (Lyc S.I. 1324C) After doing a bunch of leak snooping, I stumbled upon a spot that seemed much more like the area that the oil was coming from.  It is a plug on the front of the engine for the Prop Governor idler shaft, and is seen in this diagram as part number 6....Lycoming number 70455.

Below are a couple of photos of the plug before it came out.  As it turned out, the seal used was one of the copper crush type seals, and my only other oil leak was from one of those.  The 70455 p/n is a more standard fiber gasket washer, so I replaced it with the one in the Lyc parts manual.  I also used Loctite 515 on the threads, as recommended by Bart at Aerosport. This stuff was a little bit hard to come by, so if you ever need to do a task like this, perhaps you want to prepare in advance by getting a tube when you're visiting the right supplier.  I got it from a local bearing supply house for about $6....it's a non-hardening anaerobic sealant, but from the sounds of it, Loctite 515 is not replaced by many other types of chemicals.  The closest one I could read about on the net was Permatex #51813 Anaerobic gasket maker.  I didn't wan to risk it, so I got the real deal.

The entire job took just under 3 hours, to pull the cowl, the prop, the ring gear, and then the plug.  Then time to clean it all back up, and put it all back together.  Sure enough, the old seal wasn't torqued super tight, and it obviously had loosened (not by turning out, just by temperature cycling) over time, so it looks like it probably was the culprit.

While everything was apart, I had recently purchased a new Gates 7375XL alternator belt (11A0955) (13/32" x 38-1/8" (10mm x 967mm)) as a spare, so having nearly 5 years on this engine now, I decided to throw that on and use my original belt as the spare.

Additionally, I replaced the prop o-ring (Hartzell C-3317-228), and kept the old o-ring as a tool kit spare.

So with that all done, it was a little bit of forced worth, that accomplished a little preventative maintenance along the way. I was thrilled to see that the area on the crankshaft just outside of the front oil seal was almost completely dry, with no signs of an oil leak.  Those seals just make me nervous in that you have to stretch the new seal over the prop hub, and I wasn't excited about that.


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