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Gasoline Engine Timing

Gasoline engines have only two possibilities for their ignition, electronic or magnito. The magnito ignition timing is factory set and has virtually no adjustment. It's typacally set around 26 to 30 degrees. Electronic ignition is actually an aftermarket item and is adjustable. The adjustment varies with the engine-maker since they make the adapters for their specific engine. Regardless of how the mechanical portion is made, the actual ignition point is the same.

         Most engines using unleaded gas will time between 26 to 34 degrees. A few "hotter" engines using high octane will time up to 36 degrees. Methanol burning engines will time as high as 38 degrees and on rare occasions go as high as 40 degrees when idling isn't needed.

        The very first thing required for accurate timing is to know exactly where TDC (Top Dead Center) is. The second item needed is a way to index (in degrees) the rotation of the crankshaft. The last thing required is in fact, a good functioning ignition.

        Let's assume your ignition is working, by that I mean it sparks relaibly. So let's proceed to go through the sequence to properly get your timing right...

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#1: finding TDC
TDC is located at the extreme top of the cylinder with the piston as high as it will go. The best way (and most accurate) is to locate TDC with a dial indicator located in the sparkplug hole.

#2: rotation degrees
This will require a degree wheel of some sort that will mount on the crankshaft, or prop hub. I use a Helix 360 degree wheel. It doesn't have to be 360 though. You will also need some sort of fixed pointer mounted on the crankcase or engine mount.

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#3: time it
Turn on the ignition with a sparkplug resting on a grounded spot, and the degree wheel set to ZERO at TDC rotate the engine in the direction of the prop (normally counter clock-wise). Observe when the sparkplug fires in relation to the degree wheel. Adjust the magnet ring or sensor base to the proper setting.   

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       A lot of things go into determining where the timing ought to be for each engine. The ideal way to determine this is to time it while it's running. But most engines won't allow this. So, you will have to set it and take some RPM readings as well as observing the throttle-up accelleration. A very good starting point is +28 degrees. This is a safe and reliable point for most engines.

Make adjustments in very small increments around 2 degees or so. When you're done lock everything down TIGHT. 

* * * Electronic VS. Magnito * * *

PROS to Magnito
virtually no maintenance
no timing issues
easy airplane setup

CONS to Magnito
they are usually heavy and require a flywheel of some sort with large magnets
fixed average timing
they can be difficult to start by hand

PROS of  Electronic
easy starting (hot spark at any RPM)
can set timing for optimum performance
can have spark advance
fairly light weight

CONS of Electronic
requires a battery & maintenance
electronics are somewhat delicate
they can and will go out more often than a magnito and are sensitive to vibration