87WhiteComet

Can you index spark plugs on a rotary engine? And if so which way do you face the plugs?

Sgtblue

iTrader: (16)

With the construction of plugs that I've personally seen used in the rotary, I don't think it will make a difference.

RX744CSP

iTrader: (4)

I have to agree with Sgtblue. Indexing a plug on a piston motor generally places the negative electrode on the opposite side of the plug from the intake port, reason being the flow of the cooler denser intake charge toward the hotter leaner exhaust port. The theory is that the open side of the electrode facing the intake port allows for a quicker and more complete ignition of the fuel/air mix, as compared to the other way around which would face the open side toward the exhaust port and the intake charge diluted by remaining combustion gases. This works because the plug actually protrudes into the combustion chamber.

Rotaries 1) don't have the flow characteristics of a piston/valve combo and 2) the spark plug doesn't protrude into the combustion chamber, it's actually recessed away from it slightly.

If you look at the average rotary plug, the negative electrodes are arranged to give what's referred to in boating as a 'surface gap'. This puts the spark as close as possible to the combustion chamber, which is as close to 'indexing' as you'll get on a rotary.

87WhiteComet

I wasn't sure if there was any particular way to face the spark plug in a rotary and I totally had forgotten what the plugs looked liked since I sold my FC a while back. So to answer my own question the answers no.