A closeup of one of the spare make and break igniters for the Snow shows the fixed contact (bottom) and the swinging arm contact (top).  The shaft visible in the notch on the top of the igniter housing extends from the swinging arm contact out the back of the assembly.  When installed in the engine, the shaft is connected via a linkage to a follower that rides a cam on the sideshaft.  The follower travels up a ramp on the cam to close the contacts and allow current to flow through the contacts.  When the follower reaches the top of the cam it falls off of a step on the cam causing the contacts to open suddenly.  As the contacts open a spark jumps the gap and ignites the mixture in the cylinder.

Over time the contacts burn and pit.  They can be refurbished by applying weld buildup and then grinding them back to shape.

The engineer operates the Snow from this stand.  The handwheel at the upper left controls starting air.  The pushbutton on the box at the upper center controls the ignition.  The handwheel at upper right is for the gas supply.  The lever sets the fuel mixture.  The small handwheel at lower center is for lubricating oil supply.

 A closeup of the mixture lever, its lock knob, and the position pointer on the lever.

This large handwheel at the off side of the engine is the main shutoff for engine cooling water.  Local valves regulate water flow to individual parts of the engine.