crankcase joint seal
 

I am getting ready to reassemble my lyc 0320 d3g the overhaul manual has 3 ways to seal the case joint, silk string and pob sealer, rtv102 and permatex.
I dont have the silk string and pob sealer but I do have a tube of rtv 102. Has anyone used rtv for this step? and what were the results?
Thanks
Gregory Targonski

Permatex 3D
 

When I overhauled my engine some months back we used the Aviation Grade Permatex 3D along with the silk string. I found the Permatex at an O'Reilly Auto Parts. Its the same stuff Aircraft Spruce sells. Even has the words Aviation on the pint I bought.

I used the silk thread and Hylomar Sealant as recommended by Aircraft Specialty Services on my IO-540.
http://www.aircraft-specialties.com/...&SUBMIT=Search

His advice
 

My AP/IA said the silk thread is the key. The permatek (or whatever you use) is just there to hold the silk thread in place.

He's been assembling engines for 60+ years (FWIW).

0-320 case seal
 

For what it is worth, I have been going some issues with an )320 that was leaking at the case 1/2's. After talking to a number of A&P's I am told that the process is very tricky in getting the halves together properly. You have limited time to perform the operation and the silk thread can very easily slip off the flange (which is what happened to mine) in which case it will leak. The secret I have been told is to rehearse the procedure numberous times before hand so you will see all the required angle deflections and twists needed.
Good luck Dr Targonski

I helped a friend of mine put the heads and banks together on a Merlin. Over the years one thing P-51 operators have had trouble with is coolant leakage there. The engine builders (Nixon, Roush) have found what works best on sealing mating surfaces is good old-fashioned proseal. That's what I've been using on case halves and haven't had any trouble with it. Silk thread is a pain to deal with, POB #4 will eventually dry out, the Loctite product (hylomar?) sets up quickly so you have to be in a hurry to put the case halves together.

Bob,
Hylomar was actually developed by Rolls Royce Aircraft. It's a thick blue paste which never dries out. It's most commonly marketed by Permatex in most auto parts stores. It allows you to take your time putting the case halve together, as it won't dry [ever].
It's not the same thing as Permatex #2 or Aviation Permatex [neither of which Lycoming recommends]
I can well believe that ProSeal would work great.
Charlie Kuss

serpentine o-ring
 

I recall reading a kitplanes article a number of years back about a shop that had STCs for a bunch of engines to machine a dovetail groove around one case half for a serpentine o-ring. I thought it was a neat idea although my IO-375 will not have such an o-ring (based on Bart's recommendation).

The idea still appeals to the engineer in me.

Ly-Con in Visalia, CA are the guys doing the O-ring mod.

I will have to seal up my case halves as soon as my ECI kit arrives. My concern with using ProSeal is that you may have a terrible time getting it apart at overhaul.

AERO and ECI recommend Silk and Permatex. I have that ready to go, but always interested in a better solution.