[Robert-7]

Have a couple of questions regarding gas engine sparkplugs:

Should you get a spark/ark discharge in the silicone spark plug cap boot to ground (the outside metal cap) when the boot is not connected to the sparkplug? RCFG claim the output voltage in their RCGF ignition system (Rcexl) is 12 – 16 kV

What should the electrode gap be on a NGK BMR6A sparkplug?

[Oilsands]

Yes you can get a spark to jump from the center to the cap, but it is safer to install a spark plug and let it jump across the electrodes.

The gaps are normally around .020" or the width of an exacto blade. You could go a little wider and still be ok, but that is about the norm.

[Arceenut]

Having an excess gap (center to shell must be well over 20 - 30 thou) can cause extremely high voltages and can damage the ignition system, particularly the coil. The high voltages may break down the insulation in and around the coil and cause shorting.

[Oilsands]

Some ignitions may have issues, but some do not. I put a plug in mine just to be on the safe side, although it is not always easy to get the plug back out of the cap. If it has a c-clip around the base of the cap, I remove it which make it easier to get the plug back out. Then reinstall the clip before putting on the plug mounted on the motor.

[Robert-7]

Thanks for Oilsands and Arceenut for your responses. Originally I thought I had a leak in the silicone spark plug boot to ground BUT according to the folks at BP Hobbies (where I purchased the engine) say that to have the center pin in the plug cap arks to the metal cap/earth is normal when not attached to a sparkplug with this engine’s “High Energy” ignition system. So I have for now accepted this as fact and there is no sparkplug cap short. So I am going to start another thread that moves on to another problem with this engine.