Taken from your 1st post I also noticed that the timing chain looked as if it was off one link but I’m not entirely sure.

The first thing to do is to rebuild the engine. There is really no point speculating about how or why it broke. Rebuilding the engine properly will take care of any mechanical issues. Once that is taken care of get it tuned. Pick the tuning product of your choice and find a tuner. If you are pressed for cash find a good used engine from the bone yard or check the classifieds to help locate one.

JMC

 

Just changing the exhaust doesn't require a new tune, but you removed the cats and didn't put the O2 sensors back in. That requires a tune a tune to turn them off.

Your location will tell you who/where you can go to for tuning. Or you can order a handheld tuner from someone like Troyer Performance with tune/s pre-installed based off of your mods.

 

Those 02 sensors for the rear don't feed the engine any liable information for oky/fuel mixtures it only tells you if you have plugged cats or there is a problem with them. The car companies probably wouldn't out them in if the government didn't make them do it. You said plain and simple the exhaust is the indirect cause of the problem and I am saying that your wrong. I have the 02 simulators bought for the 02 sensors in the rear. A decrease in back pressure wouldn't effect my engine severly enough to cause engine damaging detonation.

 

At this point any more discussion about what may have caused the engine failure is a waste of bandwidth. Regardless of the outcome you need to replace the defective parts and inspect the remaining parts to insure that they don't fail. Once the engine is pronounced fit for use you can then proceed to reinstall it and get a data log to be sure you are running a program that will not cause it to self destruct all over again.

JMC

 

While I agree with JMC that trying to educate you is a waste of bandwith, I can't resist posting some common sense which I've cut and pasted from a random site on the web.

"The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before."

 

damn double post

 

did you ever check the ring gap?

 

Did you ever figure out what went wrong with your engine?

 

I worked for over 10 Years as a professional motor cycle mechanic and rebuilt lots of blown up 2 stroke engines. I have never seen one that did not mark up the aluminum combustion chamber. It looks to me like there was something wrong with the piston to begin with, a crack or something. From the pictures it looks normal and very much like the other cylinders except for the missing piece. You’re lucky that loose piece didn't take something else out. In addition a lean running engine will usually take out one of the hotter, rear cylinders first given everything else is equal.

 

I would like to hear what happened.

 

I work at a Ford Dealership here in Ontario canada and have put in many reman. engines and then had them come back with casting flaws from the rebuilder , this could simply be a problem with parts installed into your engine

 

Hard to tell from pictures, but didn't it look like they caught a ring inserting that one piston?

 

yep.