[brianwallis]

Hello folks, I just returned from some factory training from a very nice gentleman from Continental and he says... if you see RTV around the base of the cylinders(maybe it was the casehalves), that is a grounding condition... Because the RTV 1. clogs up the oil lube holes on the rockers or somewhere thereabouts (gotta read my notes) and the RTV around the base of the cylinder somehow eliminates the 14 thou of stretch of the through bolts on the case. It causes the Crank to wear on the case and makes metal and failure soon. Just thought you would like to know. Apparently RTV may be used around the base of Lycomings when changing cylinders but not continental. Hope this helps,
Brian Wallis
ps any additional input is welcome!
ps... again.. ah yes I do recall him saying application between the casehalves was the problem area... I've seen JB weld but not rtv... (not on anything I've signed off!)

 

[osxuser]

I would NEVER use rtv on an engine (aircraft or car). If you've ever seen how it interacts with oil and gas, you'd know why. There are much better alternatives if you need them. (Like proseal) I don't know why you would want to use any extra sealant when replacing cylinders anyway, the nice base seals should work fine (use new ones every time of course!).

 

[John Clark]

NEVER near a fuel system!

RTV's reaction in gasoline is something to behold. Squeeze a little out of the tube, let it set and then put it in some gasoline. A few days later it will be many times the original size. A pal of mine "sealed" the gauge sender in a car (fortunately.) The little bits that squeezed into the tank expanded and stopped up the fuel system big time.

John Clark
RV8 N18U Flying 200+
KSBA

 

[mahlon_r]

The only sealant allowed on the cylinder base of a Lycoming engine is the cylinder base o-ring with nothing else on it, but maybe a light film of oil. Any type of flexible sealant between the cylinder deck and the cylinder base is asking for big trouble. The objective is a rigid metal-to-metal parting surface connection. Any movement that could be allowed even the smallest amount of movement between the cylinder and the crankcase will allow the cylinder to move outward against the cylinder base nuts every time the cylinder fires. This will eventually allow excessive crankcase fretting at both the main bearing parting surface and also the cylinder base to cylinder deck surface. The later causes the cylinder base studs to fail from the continual pounding they are taking...sort of like a jack hammer working against the cylinder base nuts trying to break the cylinder base studs. If one of the studs fails which is inevitable the rest will shortly follow, this will cause eventual departure of the cylinder and the other situation of excessive case fretting at the main bearing bores can cause excessive oil leaks and main bearing shell movement which could lead to failure there.
I would not recommend any sealant between the cylinder decks and crankcase, of any aircraft engine, other then the cylinder base O-ring supplied for that purpose.
Maybe your instructor was referring to sealant between the crankcase halves? Lycoming does allow the use of a thin film of RTV 102 flexible sealant between the cases on assembly, but even that practice can be dangerous if not done properly. We use silk thread and POB #4. Perfect Seal there.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."