Because it's supposed to. Some turn clockwise, some counter clockwise. Why? You would have to ask the design engineer but I suspect it has to do with patent rights. A Buick and an Olds. engine could be the same design and if the distributor turns in a different direction, it can be claimed as a different design.
Clockwise.
Rotor turns counterclockwise.
Depending on the make of the helicopter, some will rotate clockwise and others will rotate counter-clockwise. However, the main rotor and tail rotor will spin opposite of each other. If the tail rotor spins clockwise, the main rotor will spin counter-clockwise. The main rotor also spins for lift, the tail rotor for control.
1-3-4-2 Rotor turns clockwise. You can easily find this out on any engine by removing the distributor cap and turning the engine over while observing the rotation of the rotor.
Rotor turns clockwise.
Engine rotation is determined by sitting in the driver's seat. But engine rotation is of no consequence when determine firing order. It is the rotation of the rotor in the distributor that is important. That is easily found by removing the distributor cap and bumping the engine over and looking at the rotor. Does it rotate clockwise or counter clockwise?
The tail rotor is moving "perpendicular" to the main rotor, not "opposite". The tail rotor creates thrust opposite to the thrust of the main rotor, to keep the fuselage from spinning. Most helicopters spin the main rotor counter-clockwise looking from above, which puts a clockwise rotation on the fuselage. You need a tail rotor pushing the tail counter-clockwise to keep the fuselage pointed in the direction the pilot chooses.
The firing order is 1-3-4-2. The rotor rotates counter clockwise
To advance, rotate the distributor counter-clockwise. To retard, roatate it clockwise).
Ford V8 engines fire with the distrbutor rotor rotating couter-clockwise.
Counter clockwise
Rtr. turning clockwise. Rotate distributor counter clockwise to advance timing, clockwise to retard.