Installing push rod tubes with silicone seals
We recently installed to overhauled cylinders in our 108-2 with a Franklin 165. The biggest challenge of the whole ordeal was reinstalling the pushrod tubes with the new silicone seals. What a PAIN in the #!+$!
Does anybody have a process to make this easy?
When I installed mine I took the gaskets and just broke the edge that goes into the engine and cylinder on a bench grinder to give them a slight chamfer. I then used goop hand cleaner as a lube as it will burn off when the engine becomes hot. Next get a piece of dowel rod and whittle down the end. As you are pushing the tube into place the cylinder side should slide in fairly easily. Use the dowel to help the engine side into place. Yes it is a pain but I have not had any leaks so far on mine. The dowel should not be whittled to a point but enough so that it will fit between the tube and the case. Hope this helps.
Thank you for the tips. We basically used the same procedure but with different tools. However I lubed the seals with Aeroshell. The point you made about the hand cleaner burning off is good as the result may be a better seal.
It just seemed strange to me that there is no mechanical means of preventing them from coming out.
Although I have not flown the plane extensively since replacing the two cylinders it appears that we have no leaks after the 15 minute ground runup. Which is refreshing!
Basically they are held in place by the valve cover and friction. They are not under any kind of load they are just a tunnel for the pushrod to operate in so we don't sling oil all over the place.
I have found the silicone push rod cover seals unnecessaily difficult to install. I think they are often slightly oversize. However if you insist on using them the best lube for inserting them is the Dow Corning DC4 silicone that every aircraft owner needs to have a tube of it. Avaiable from spruce and probably your local industrial bearing supplier. But I still prefer the original black rubber packings as being easier to install,. When I installed mine in 1983 using the silicone it was more than 5 years and 500 hrs before I ever noticed some seeping.
Franklins develop oil leaks, mainly on the push rod tubes mostly because only Franklins have solid aluminum cylinders with steel liners which expand and contract more with every heat cycle than do the steel cylinders with aluminum screwed on heads that the others use.