Spark plug colors and paranoia

[kevinh]

Hi ya'll,

I just removed, cleaned and gapped the plugs on my O-360-A1A. For the second time, I noticed that the cylinder two bottom plug was darker than the other three bottom plugs.

On the top plugs I'm running auto plugs and Lightspeed electronic ignition - those always look the same. The bottoms are aviation plugs driven by a mag.

I've also noticed that the cylinder two EGT has been running about 70 degrees higher than the other cylinders. The CHTs are all very close, with the rear cylinders being unsurprisingly a little bit warmer.

The engine only has 175 hrs on it.

Should I be concerned? What should I keep an eye out for?

Any advice would be appreciated.

Kevin

[RV6_flyer]

If the EGT is higher on the number two cylinder, maybe the massive electrote bottom plug is not firing.

On a dual mag engine, you rotate plugs top to bottom next in firing order. Since you have Lightspeed on the top, try rotating the bottom plugs to the next positon in firing order. If the high EGT follows the plug, the plug maybe bad.

[kevinh]

Originally Posted by RV6_flyer

If the EGT is higher on the number two cylinder, maybe the massive electrote bottom plug is not firing.

On a dual mag engine, you rotate plugs top to bottom next in firing order. Since you have Lightspeed on the top, try rotating the bottom plugs to the next positon in firing order. If the high EGT follows the plug, the plug maybe bad.

Thanks for the quick reply.

btw: If I run the engine just on the mag it still runs smooth (well - smooth for 1 mag). Could the plug still be bad?

I've moved the plug to a different cylinder, we'll see if the high temp moves with it.

[dan]

Originally Posted by kevinh

I've moved the plug to a different cylinder, we'll see if the high temp moves with it.

If not, you might check for an intake leak on the high EGT cyl.

[kevinh]

Originally Posted by dan

If not, you might check for an intake leak on the high EGT cyl.

Good call - thanks.