Page 26 - TTFebruary2018

Cracked Cylinders
During a routine inspection, a cracked cylinder was found requiring replacement. This was the latest AOG event related to a long series of cylinder problems.
by Kevin Ware
What previously was a smooth, aerodynamic engine cowl is now laying on the han- gar’s concrete floor with various parts never intended for public viewing being ex- posed in all their tangled awkwardness for any passerby to see. Within this jumble
of tubes, wires and other objects mounted on various odd-shaped brackets, there is a small spark plug opening, and next to that a half-inch black line from which there extends an ominous blue stain. The stain results from the fact that 100LL fuel has mixed with it a blue dye, and when it leaks out through a crack in a cylinder head, it leaves a trail of blue pigment running uncomfortably close to the nearby Mexhaust stack.
To make matters worse, Paul the mechanic says the No.1 cylinder on the opposite (right) engine also has low compression, but he has not (yet) been able to find a crack. The involved cylinders, of course, are located on the far back side of the engines and almost impossible to see unless gifted with extraordinary eyesight, a very bright light, plus a huge dental mirror, and un- matched mechanical ability. Nevertheless, in spite of this difficulty, Paul an airplane mechanic of great aptitude, had just managed to find at least the one crack during a routine exhaust inspection and oil change on my Cessna 340.
Given the possibility that there may be some carbon deposit within the cylinder on the right side that is interfering with compression, what he now wants me to do is fly the airplane for 30 minutes or so, running the right en- gine through peak EGT a couple of times, to see if it can be burned off. That sounds OK, until he also says I should not operate the left engine with the visibly cracked cylinder and leaking fuel at anything but very reduced power.
Luckily, a lightly loaded RSTOL C340 is quite a performer. After carefully making sure all the cowls are back in place, I taxi out for the required maintenance flight. Getting on the runway, I mentally brief myself on single-engine procedures, then gradually push the right engines throttle to the stop, while holding the left engine no more than 30 inches of MP. A bit of fiddling is needed with the rudder pedals to keep the airplane on the white line with the differential power setting, but otherwise the airplane accelerates just fine, and I shortly find myself at 5,500 feet out over the Cascades cycling the right engine, while the left is kept down to not much more than idle power.
24 • TWIN & TURBINE
February 2018