While discussing maintenance issues with other Lancairians, I have found that many are not aware of a particular maintenance check on the nose strut which should be done at least annually.  It involves a potential leak path for the strut oil to escape undetected.  This of course can lead to such unpleasant things such as loss of shimmy damping followed by broken mounts and engine and prop rebuilds etc.

The interior of the strut tube can slowly fill with strut oil if one of two very small O-rings starts to leak.  The O-rings are located in what is called the guide key retainer.  You can see the guide key retainer if you look up inside the nose strut with the fork removed.  There are a few versions out there.  Some are steel and rectangular, while older versions are triangular and are made of aluminum.  There are two 5-40 screws that penetrate through the wall of the strut tube and are screwed into the guide key retainer.  Counter bores in the guide key retainer capture two tiny O-rings that hold back strut oil.  Because these screws are in the shimmy damper area, they are submerged in oil.  Therefore, if there is a leak, the strut will not loose noticeable pressure, just oil.  The interior of the strut tube should be checked for oil leakage.  If the leak is bad, accumulated oil will run out as soon as the fork is loosened.  If the leak is light the inner walls of the tube will be damp with oil.  Replacing the O-rings requires a complete tear down.  Unfortunately the guide key and guide key retainer are at the very core of the strut. 

This is one of those items that should not be overlooked as it could cost you (or your insurance company) a bundle.

 

 

Chris Zavatson

N91CZ

360std

www.N91CZ.com