Re: 1959 Flying Scott 75hp motor

[amuller]

The point of grounding the plug wires is that if the magneto coils are "open circuit" high voltages can be created that can puncture insulation. Normally, the voltage is limited to that needed to spark across the plug gap. So whenever the motor is cranked over, as for a compression check, with the plug wires disconnected, the plug wires should be shorted to ground. I have a pair of plugs with wire taped to the shells and an alligator clip on the other end.
Of course if there is a magneto kill switch of some sort that will also work.

Lots of people do compression checks without bothering with this and get away with it, but…..