I am plotting out the re-assembly of my 2.2 wbxer, and thought I would ask about 
a bit of Lycoming/Continental lore that I was recently exposed to. 

For those who are unfamiliar with these engines, they are horizontally-opposed, 
air-cooled four cylinder engines, used to power many, if not MOST light civilian 
aircraft. Structurally, they are very similar to our versions of infernal 
combustion units�that power our VWs. Vertically-split on the center-line, 
separate cylinder jugs, etc. They, and their maintenance,�fall under the purview 
of the exceedingly conservative (mechanically) FAA.

When sealing the case halves together on these engines, two things are 
used.�Permatex Aviation sealant and silk thread. (Permatex is the only FAA 
approved sealant.) But that's not my point. The interesting thing is that a silk 
(real silk, not polyester) thread is carefully laid down on one side of the 
sealing surface, in the sealing compound, before the halves are fitted together. 
Does anyone know if this trick has been tried on any of the VW cases, and if 
not, why not? There must be some advantage, my guess is in filling the small 
crevices that machining processes leave, that the sealing compound alone can't 
cope with. The thread itself can't be thick enough to interfere with the fit 
between the halves, can it? If this is an improvement for oil sealing, I am all 
in favor of it! It may just be there to keep the halves far enough apart for the 
Permatex to work properly, or maybe as a method to keep the halves from 
"working" against each other at the seam.

Enquiring minds want to know...