Damn, that sucks, you worked your *** off in the cold to get 'er together too. Hope you find an even better engine next time.

Sorry to here that your new replacement engine has failed . Its never fun to have to redo a job .

Sad part is that was a good motor, that'* why you picked it up.

I'm thinking of a few things that might have caused it. The 3M cleaning discs that I use come with a warning on them about aluminum and the correct pad for the metal, as well GM put out a TSB type of warning to all mechanics that specificially said not to use those as they could get into the motor and destroy bearings. While no mechanic in the world took that seriously or stopped using them, GM did publish it for a reason. That material is hard enough that it would destroy bearings if it gets into the oil supply.

ps. by the time I got to motor #3 I had a routine of cheap walmart oil for two changes in the first 2-5 minutes of start up and then another in about 100 miles to swap back to synthetic. The next change was maybe at 500 miles. Tell me I wasn't spooked or worried...

I did not use the 3M pad, I used a brass scrapper.

I think next engine is going to get several oil changes.

I started questioning everything I did and every part I used.

So far you questioned the cam. Said to me you thought it was loose in the bearings and possibly starving the bottom end. I suppose, yet they had good oil for a while.

You are questioning the flex as being off balance etc. Yet it'* a rod bearing not a main bearing. The mains hold the crank in place and should take the brunt of something being off balance. I've seen cracked flexplates and bad harmonic balancers run for quite a while w/o hurting a bearing. Expecially a rod bearing.

Likely..it'* simply a piece of bad luck or a transplant that didn't take.

That is possible. However, I want to start testing things. That'* why I want to test run out on the flex plate when it'* out. I'm also going to tear the block down to find the problem. The bad area seems to be in the #5, #6 area.

Positive all the wires were on the right cylinders?

100% positive.

Ok, I've seen some close enough that cause a vibration and it'* very tough to notice. Still thinking about that vibration you talked about.

My build up went like this
Pulled motor, Ooopsied, installed.
Pulled it again to fix 180 degree off flex. Oops again
It died in 200 miles
Put in another motor drove 10 miles (found out it had been on a shelf for over 2 years)
Put in the third, by now I was proficent, and my forearms hurt from swapping the valve springs.

I've got things to look at, that'* for sure. But like you said, a engine with nearly 200k on it may have just not been up to the challenge.