Why Apex Seals Fail

[vex]

Originally Posted by Barry Bordes

A couple of observations.

Detonation can be a cause of breaking apex seals but it is not a root cause.

Leaning out at high boost and too much advance can be a root causes, but how many of us run conservative maps and still have problems? There is something else going on.

Also, no one has brought up the warping of apex seals. Using OEM I haven't seen this. Can anyone share their experiences with this problem?

Barry

My only experience of warping apex seals comes from when I was running OEM 3-piece seals. They didn't warp enough to cause failure before the 'fire control ring' let go, but they tended to warp concavely (ie The center of the seal moved to be closer to the eccentric shaft). I doubt this would cause the failure we're seeing. Convex warping may prove more of an issue; and may be indicative of the material selected for the seals.

Also the leaning out of the AFR does not necessarily have to be in positive pressure to cause the issues of thermal induced mechanical interference. Note that the SAE paper only took the motors up to 5000 RPM for 45 seconds. They were not in positive pressure, but were loaded. The result can be the same and is dependent upon the AFR and the resultant flame front temperature.

If you look at the picture I posted previously, I would assume that the peak temperature would appear at the peak temperature at normal operation (assuming timing remains constant and the fuel itself is adjusted). This means if we're running lean AFR at normal timing the result is going to be increased temperature at the Leading spark plug boss, where we may, or may not have appropriate energy transfer.