Piston Damage

["Bruce Hevner" <scramblr@xxxxxxxxxxxxx>]

> But actually my pistons broke chunks off the top ring land.  The dish 
> and the valve relief in the 1970 390 comes very close to the top ring 
> groove.

This kind of damage is usually due to detonation and or insufficient ring
end gap. I have seen this type damage MANY times on stock motors where the
EGR valve stops working. There is also inaudible detonation. Just because
you can not hear it "ping" does NOT mean you are not having detonation.

>From http://www.speedomotive.com/building%20tips.htm
"Top Ring End Gap is often a major player when it comes to piston problems.
Top ring butting under high load and heat conditions can destroy the piston
top land. Most top land damage on race pistons appears to lift into the
combustion chamber. The reason is that the top ring ends butt and stick
tight at top-dead-center. Crank rotation pulls the piston down the cylinder
while leaving at least part of the ring and top land at top-dead. Actual end
gap will vary depending on the engine heat load."

Bruce Hevner