Being unfamiliar with the imperial system of units an engine volume of 360 cubicle inches might not trigger one’s imagination. However if we look at this value the metric way, this little powerhorse proves to encompass a cylinder capacity of 5.9 liter. Have you ever felt the excitation of throttling up a 5.9 liter automobile? …Right, so maybe that’s a first good reason to treat this engine with respect!
Another difference compared to the engine in most common cars is their manufacturing process. Instead of being built on high volume automated production lines, Lycoming engines are entirely hand built to particular airframe manufacturer’s specifications on a single assembly line in Williamsport, Pennsylvania. Furthermore due to their specific application, production volumes are much lower. It shouldn’t be a surprise that a new engine comes in at a cost of about $55.000. …Another good reason to show some dignity when putting your hand on the throttle.
A lot of information on the construction and sound operation of the IO-360-L2A can be found in both the Cessna and Lycoming IO-360 operator’s manuals. In addition, the Lycoming website contains an extensive database on both technical and operational recommendations on treating your engine the way it should be treated.
Do you still remember the limitations on engine speed drop when checking the magneto’s? …and what are we actually looking for when when performing the magneto check?
In order to initiate the combustion process in a gasoline engine there is a need for fuel, oxygen and an ignition source. Hence a cylinder needs to contain at least one working spark plug which ignites the combustible fuel and air mixture which is drawn into the cylinder during the induction stroke. It’s pretty simple: no ignition means no combustion …and no combustion means the affected cylinder is not driving the crankshaft hence propeller.
In order to increase engine reliability, gasoline engines have been equipped with 2 spark plugs per cylinder for decades. In case 1 plug fails, proper combustion is ensured by the second redundant plug. To improve reliability even further, those spark plugs are powered by two independent engine driven electrical generators, which are called magnetos. Each individual magneto serves all cylinders by a discrete set of ignition leads and sprak plugs. This is clearly shown in the wiring diagram above.
Nowadays most gasoline engines are fitted with electronic ignition units and a single set of spark plugs. However, with an eye on reliability, the IO-360-L2A sticks to the mechanically timed Slick magnetos which keep on sparking the plugs as long as the engine is running.
Since ignition in the IO-360-L2A is initiated by 2 spark plugs, the fuel-air mixture contained in the cylinders is ignited at two different locations within the cylinder. This causes total combustion within the entire cylinder volume to be reached at a faster rate causing an increase in torque and hence power. Simply stated: for a particular throttle setting, the RPM will be higher.
No reason for cold sweat, we won’t describe the construction of the magneto! The only important thing to remember is that each magneto does 2 things:
So, what is the magneto check all about? Let’s start with Lycoming’s procedure which corresponds to the procedure stated in the Cessna POH.
Having this check procedure in mind you might wonder why the RPM is supposed to drop when running the engine on a single magneto. The answer is simple: as the air-fuel mixture is ignited from a single spark plug, total combustion within the entire cylinder volume will be reached at a slower rate. For a particular throttle setting this causes engine torque and power to decrease. Simply stated: the RPM will drop.
So what might go wrong during the magneto check? If the engine stops when running on a single magneto, this indicates that none of the cylinders are being fired by that particular magneto. Most likely this is caused by the magneto failing to generate electrical power to feed the plugs. This might be due to a failure of the magneto’s generator, or a deficiency in the magneto’s control wiring originating from the magneto switch.
Please SHARE your experiences with any Magneto Issues you have ever encountered throughout your aviation career, we'd love to hear from you!