since 1940

Lycoming Aircraft Engine Nose Seal Leakage. Crank seal leaking

Lycoming LW-11997 crankshaft nose seal

Continued problems with nose seals leaking on Lycoming engines may be caused by the fit between the crankcase and crankshaft. If you have inspected the crankshaft seal to confirm the proper type, installation, crankshaft surface finish, crankcase pressurization, but still have a seal problem, then it's time to start looking elsewhere. Buying an exchange or welded crankcase and replacement crankshaft means the crankshaft may not be mated properly to the crankcase. Three subtle engine conditions may make it impossible to seal the crankshaft, These are:

 1. Excessive clearance between the main crankshaft bearing and crankshaft journal which allows more oil to leak out of the bearing shell, thereby delivering more oil to the crankshaft oil slinger.

 2. A bent oil slinger. As the crankshaft rotates, the slinger wobbles, thereby becoming an efficient oil pump.

 3. Not enough clearance between the front slinger face of the crankshaft and the crankshaft nose seal retainer. Lack of clearance will trap oil and sling it forward into the seal. If you have any of these conditions, it requires complete engine removal and disassembly to correct. How do you inspect for these conditions without disassembling the engine?

With the nose seal removed, pull the crankshaft forward. The crankshaft thrust face will now be against the crankcase thrust face. There should now be 2 to 7 thousandths clearance between the crankshaft slinger and the nose seal retainer. Slip a piece of paper in behind the nose seal casting on the crankcase and see if it fits between the casting and the crankshaft slinger. If it does not fit, you do not have the proper clearance. Rotate the crankshaft, making sure it stays forward and see if the clearance oscillates. If it does, the slinger is bent and will pump oil into the seal. If you do not have at least 2 thousandths (preferably not fewer than 5 thousandths) clearance, how do you change it? The Lycoming overhaul manual explains how to grind the face of the oil slinger until you get the proper clearance. Any time you inspect a crankshaft for run-out, also inspect the crankshaft slinger and check the clearance between the slinger and crankcase when you lay the crankshaft into the case during re-assembly.

4. A rare condition may exist where the crankshaft seal leaks or is pushed partially out and there is aluminum in the engine oil. This occurs when there is a failure of the crankshaft thrust face. One cause is a crankshaft who's "white layer" is left remaining on the thrust face after Nitriding. This surface wears into the crankcase bearing surface.
 
 

Copyright 1995 by Sacramento Sky Ranch Inc. All rights reserved. 

 

Copyright 2003 by Sacramento Sky Ranch Inc. All rights reserved.  Prices subject to change without notice. Not responsible for typographical or misprint.
Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.