[BruceWilkie]

Preignition takes out pistons faster than you can imagine and in my case no warning. 3 times in one month on a 2 stroke I had pistons that looked like someone took a plasma cutter to the center. (plus "plasma" spray on cylinder walls and ports) In my case it was the aftermarket pipe I was using wasnt compatible with the porting I did. Changing to a race pipe from another manufacturer it never occured again. Tune up remained the same, performance was "maybe" better. My burn downs were occuring after a long pass off throttle shortly then back near full throttle. I'd hear a strange "gurgle" and the motor stopped near simultaneously. That motor then went 2 seasons without issue. Later experiments with timing could produce detonation that was quite audible yet broke nothing. Dialing in a different set of carbs I pinched a ring. Resolved that and used the sled more for trail use(aggressive) than racing. When I finally retired that sled after 7 years the chassis was whipped the clutches well worn and the roller bearings in the crankcase fit rather loose.

The 460 Ford I put together was (when I first tore it down) a great example of detonation effects. All 8 rod bearings were copper on top and fine on the bottom. The mains had copper on the lower shells opposite the piston travel. Lots of miles on a pinging engine is my conclusion. Motor came out of a 76 Lincoln. Chances are the owner never heard it or just ignored it. The car had been retired with a burnt up trans.