Ignition question/issue....
 

Can some of you folks answer a few possibly somewhat silly questions?

1) Which mag is right and which is left on our IO-360-G engines? Is it left and right as viewed from behind the engine or standing in front of the engine at the spinner?

2) If I put the mag switch on "R" on the rear engine and cylinder #5 drops off line, which plug is bad? Is it the top one or the bottom one? Also, I assume in this case, I am turning off the left mag when I put the switch to "R". Is this true?

Thanks for the help.

I'll be a little more detailed with my issue when I have more time to type.

Ed

The mags are left-right as viewed from behind the engine looking at the prop.

The right mag fires the top plugs on the right side and the bottom plugs on the left side. IOW, the mag fires the top plugs on it's own side, bottom plugs on the other side.

In your example, the top plug on #5 is bad.

If wired correctly, when you select LEFT, the right mag is turned off.

Does that help?

Thanks Walter and yes this does help.

The behavior of number 5 on the rear engine is somewhat interesting to me. I'm not sure what to think. About every 20 hours or so I will lose number 5 on the right mag, rear engine. I do ignition checks at altitude and today was the day that number 5 dropped off on the right mag.

My M/O is to just pull both plugs (because I never knew if it was the top or bottom plug), clean them up, test them (always test good), put them back in and go fly. The problem goes away for 20 to 25 hours and then reappears. The eleven other cylinders do not do this but it is always number 5 on the rear. I think last time I rotated the plugs in number 5 to see if the problem would follow the plug. It appears it did not but I can't remember for sure if I did in fact rotate the plugs. Needed to take better notes as it was about 4 months ago.

Anyway, tomorrow the top plug on number 5 is getting replaced with a brand new one and I'll see what happens.

Thanks Walter.

Ed

What you are experiencing is the incipient failure of the plug. I have a bushel basket full of plugs that are bad, but TEST good on a bomb test. Replacing plugs that act like this at your earliest convenience is a very good idea.

Plug was replaced today with a new one. It even tested bad this time which I was happy to see.

Thanks for the help Walter.

Ed

Any time. Remember that the best way to test an ignition system is during an in-flight, high power LOP mag check. Weak plugs will show themselves very early on. Change 'em before they interfere with your family trip to grandma's house!

Yep....this one was caught on my usual in flight mag checks. Ground run was fine before take-off. 15 min later at 9,500 feet, the plug was just along for the ride. :o)