New versus used engine to replace 2008 Camry engine

Curious about this 2AZ-FE engine, what is the cause of the apparent piston/ring problem? Seems unusual for something like this to occur at Toyota. Some form of metal contamination making the parts weaker than they were predicted to be? A dimensional problem in the parts not caught by the manufacturing engineers? Or a fundamental design problem?

@GeorgeSanJose

I believe Toyota is better at covering up their f . . . ups than some other manufacturers. When I occasionally log onto the Toyota technical website, I see stuff that would blow your mind.

FWIW . . . here’s that information

http://www.rav4world.com/tsb/2011/T-SB-0094-11.pdf

References seem to correct problems with certain parts dimensions and head warp-age from what I can see there. Thanks for the link dB.