National Aeronca Association Bulletin Board

7AC cylinder damage
A75 Continental
Annual time.
Removed wires from all four top plugs. AI installed plugs last year.
Applied a 7/8” deep socket on a conventional ½” socket wrench. Nothing moved.
Found a cheater pipe. Applied slowly increasing force at about normal breaker bar length.
Judged that excessive force was required to loosen the plugs. Three of them abruptly loosened with a cracking or popping sound.
The right rear plug did not break free. Instead, whatever it is located in began to rotate. I turned it about one revolution and decided something was very wrong.
Work stopped.
Initial impression:
Overtorqued plugs and/or insufficient anti-seize compound.
I don’t know if the sleeve the plug is located in is a threaded or shrink fit device.
How do I approach it?
Meanwhile there are four bottom plugs to remove. How to do that?
I suggest using a torque wrench. It should require no more than 30 ft/lbs. If it exceeds that, what do I do?
Perhaps run the engine. It might be easier to remove the plugs from a hot engine. This worked for me when removing a tight oil filter cover bolt from a motorcycle once.
Thanks for all advice.
Jim Heidere
1946 7AC
N7125

Try it hot. As for the plug you moved but can't get out, you sheared the brass dowel that hold the brass plug adapter (that's screwed in) in place. You're going to have to either take it out or if the plug comes loose, drill out the dowel and replace it.
I think your mechanic should re-calibrate his torque wrench or arm.

Thanks Al
Jim

Jim,
Al nailed it. You will need to pull the insert and redowel it. The Continental Service manual has the proceedures. The inserts come in oversizes if you require one.
You might take a 18MM tap and clean out the remaining holes.
Most people tend to overtighten the plugs and everything else.
Paul

Thank you Paul.
Jim

Al, Paul,
I really appreciate your help. Some followup questions?
Who makes the aluminum bronze inserts?
How snug do they need to be when screwed into the cylinder? Obviously the dowel pin has to line up with a groove in the insert.
Do you use Lock-Tite on the threads?
You referred to the Continental service manual. Can you give me a complete title and maybe I can find one online? I have found the operators manual which only describes the cylinders.
Jim Heidere
N7125

Jim,
The operating manual has the info, pg 31 item2.b.(6) has the replacement procedure, and pg 46 has the installation specs.
Clean it up, smooth out the interface and install it with some green sleeve-lock. I'll keep looking for the spec's on the dowel hole.
Paul

Thanks again. I am indebted.
Jim