Hi360’ ... it didn’t occur to me both pistons rising and falling in tandem. The difference being which stroke they each experience. Hmmm
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Allow me to think out loud: as one piston is on its compression stroke (both valves closed), the other must be on its exhaust stroke (exhaust valve open). So In 4 strokes, the engine -as a whole - experiences a compression/spark-inspired combustion event every other stroke.
From a timing perspective, shouldn’t the point for each cylinder close to make contact on its respective compression stroke as that cylinder reaches either TDC or just before? In your explanation, you indicate points are open at TDC... I’m missing something.
The coil fires through induced voltage, there are two coils of wire within an ignition coil, a high current low voltage primary and a ha high voltage low current secondary so works opposite to what you would think, when the points close they charge up the primary side of the coil, when the points open the breakdown of the charge causes a change in the magnetic flux in the primary coil, this induces a current in the secondary coil as the windings are wound so they are concentric with the primary coil windings.
The ratio of turns in the coil is roughly 100:1 - the voltage induced is in a similar ratio. Depending on the number of turns in the primary and The number of turns in the secondary, the induced voltage secondary windings when the points open can be high (20,000 Volts).
If your ignition timing is correctly set the points will open at 14 degrees before TDC, close enough to be an indicator of piston position for kickstarting.