You may have a "point" there, Pete; the detonation could result from a combination of factors. This much I know: the ATU slot gets slammed violently against the pin on both sides when the malfunction occurs. There's sudden rpm change every time you shift gears, engine brake, or declutch, for example--ATU spins at high rpm with camshaft, camshaft slows suddenly, ATU doesn't, impact results. Lay on throttle after the shift, etc., and impact results on the other side. The slot widens. Maybe under steady throttle your spring-tension hypothesis holds and the points cam is held to the advance side under cruising conditions as well--Hell, I don't know, I just know what's there when I open 'em up and what usually happens to the piston when that little rascal does a comealoose!
