To make a long story short, I had a motor lean out a bit under boost (15psi with AFR's in the low-mid 12s) and it popped.



Pulling the motor down revealed a seal had fallen out of the rotor and munched itself. All pretty standard stuff. However, on each rotor face there is a small area where all the carbon had been blown/cleaned off. This was right next to the centre of the apex seals. There is one of these marks next to each apex seal but only on one side of the seal. At the point where the ignition fires this would be at the bottom of the combustion chamber.



My question is what causes the marks? I am suspecting detonation may of blown the carbon off. However, I always thought the flame front moved up the combustion chamber not down it. If this is the case I would have expected the marks at the other end of the rotor face.



Anyone have any experience on this?

got a pic? Could be chatter

Is the setup running wasted spark? If so then this late ignition takes place right before the apex seal passes over the leading plug.



I am pretty sure this is exactly what you see.

[quote name='ArmyOfOne' date='Apr 12 2005, 11:00 AM']Is the setup running wasted spark? If so then this late ignition takes place right before the apex seal passes over the leading plug.



I am pretty sure this is exactly what you see.


[/quote]



Ditto............on that https://www.nopistons.com/forums/pub...1047683683.gif https://www.nopistons.com/forums/pub...1047683827.gif

That makes perfect sense. I think that's exactly what it is. Guess I overlooked the obvious. Thanks fellas.

Sounds like the marks are from the oil injectors. Normal wear.

chuck