Engine work: Ignition

The ignition systems on most small planes are dated technology that are relatively reliable, but require frequent maintenance and don't deliver very good performance. When I got the project, it had 2 magentos - Slick brand 4370 on the left ignition and a Slick 4371 on the right ignition. Kind of like nuke plants, there are 2 (or more) of everything. In case one ignition breaks, you have another one. For those not in the know, each ignition system delivers a spark to each cylinder. If you're good at math you'll realize that this means a 4 cylinder engine has 8 spark plugs. Sounds great, until you find out that some of these spark plugs can cost $50 each, or more.

So what's the answer? Fortunately, engines in airplanes work the same way the ones in your car do. Except your car has better performance than the typical airplane engine because it has fancy electronics that use solid state sensors. Well, cars abandoned distributors sometime in the 90's (I think?) and went to electronic ignitions. These are finally being adapted to airplanes. Now, why go with electronic ignition? Well, for one the maintenance is non-existent... you don't have to rebuild it every 500 hour (or less). You don't have power being robbed from the crank and accessory case. The spark advance is variable with manifold pressure (as it should be). Mags run fixed spark advance timing so your engine won't run optimally across the rpm range. They are lighter (weight reduction is a big deal in small planes). It uses regular car spark plugs (about $2.50 each). Oh, and it makes the engine run smoother, easier to start, and the spark is more efficient so you can reduce the mixture to run lean of peak and save gas. Of course, there's no free lunch. The downside? Unknown failure modes, electronics could shit the bed, sensitive to heat, might have electromagnetic noise (bad for navigation radios), and ... it needs power to run. The mags run straight off the engine.

I chose an E-mag air PMag model 114. The reason I went with this brand instead of something else was:

• long time on the market
• good performance reviews
• no need for electrical power (internally powered)
• plus, they are a Texas company!

So, last weekend I pulled the old Slick 4370 magneto off the left side of the ignition to make way for the PMag. The 4731 will stay because it is the impulse magneto, which basically means it has extra pieces parts that allow it to start the engine. This means I can start the engine with either the left side 4371 magneto, or with the new PMag, or ideally both. Plus, I needed the accessory case drive gear  from the old 4370 for the new PMag. Some people replace the 4371 since it has more moving parts and needs a 1 inch spacer (weight). I figure I'll start here, and maybe down the line upgrade the left one.