Grounding plugs

[calvin]

When checking compresion on motors without kill switches does it matter if the plugs are still in the boots or out..the reason some have questioned weather it harms the coils..on older points motors?

[Mark75H]

It can damage the coil on any motor.

Not grounding the plugs makes the spark seek an alternate path which will damage the insulation of the coil. Providing a path to ground pervents the search for an alternate.

[russhill]

Sam,
I gotta keep you honest. I agree with some of what you say but it's a little too broad for me. "It can damage the coil on any motor." CAN? Yeah, I guess it CAN; I've heard this all my life. However I've never seen a coil demonstratively ruined because of not grounding.

Also what you say applies only to a magnito ignition engines. Switch "off" on a battery ignition causes no harm or no risk to anything. A magnito with a kill switch could be exposed to risk you cite dependant on the circuitry of the kill switch.

I also think if you'e going to play the "coil protect" game, I prefer going directly to the ground, not via a spark plug. For example on a spilled engine washed with fuel, a fire could be caused by the spark in the spark plug.

[Mark75H]

I like what you said Russ :)