So I recently ended up purchasing an 07 250, I purchased the truck non running and found out it had a destroyed flex plate.

I removed the transmission, replaced the flex plate, started the truck, and it ran rough, sounded like metal on metal in the flexplate area. Checked the torque on the torque converter nuts and it was all in spec, but I also noticed oil on the flexplate.

I'm thinking something is obviously wrong with the engine and likely caused the first flexplate to crack- but what would cause this? Everything else in the engine seems pretty solid, injectors, oil pressure, etc, just this lower end problem.

I'm replacing the whole drivetrain in the truck just to be on the safe side, but I want to correct this engine and keep it on the shelf for the next truck- anything standing out? Spun bearing make the crank out of balance perhaps?

 

Typically, the transmission not bolted correctly to the engine, making the flex plate flex unevenly, they are not supposed to; incorrectly installed torque converter, damaging the pump also.

 

Torque converter was seated properly, I made sure to check that after I removed the transmission, truck drives fine.

What do you mean by the transmission not bolted to the engine correctly- all the bolts went back in with no issues, I didn't notice anything out of the ordinary, and it's not my first trans/engine R&R

 

If there is any debris that gets caught between the mounting surfaces on one side, the transmission main shaft centerline is off compared to the crankshaft centerline.

 

Interesting - I didn't notice anything when it went back together.

I'm debating if I want to just replace the engine/trans and be done with it (I have a known good donor) or if I want to drop the trans again and try and figure it out. Trans is a bear to get in and out with just a floor jack in the garage, and I'd hate to remove it only to not figure out and have to take it back out.

I did start the truck without the trans installed, and noticed it did have a slight shake to it, but figured that was because of the lack of transmission being installed.

 

I wouldn't dismiss the shake. If the previous owner had a hydrolock condition they could have bent a rod. That imbalance could set up a harmonic that could crack the flexplate. I've never had the issue.

 

The truck was purchased from insurance auction as a theft recovery. It was recovered but had a bad flex plate.

I've only seen hydrolocks from either injectors hanging open, or coolant. Injectors are all functioning perfectly, and coolant was full. I'm sure it was stolen, and then abandoned when they cracked the flexplate, towed to insurance auction, and sold. Engine fired off instantly and had no signs of hydrolock upon flexplate reinstall.

The only thing I thought of is perhaps a partially spun bearing or something along those lines that would have caused it, but I'm not sure.

 

You don't know the long history, and we can speculate all day. You don't know it's history, did it have a hydrolock, injector fixed, or an EGR cooler and replaced, the owner had the issue and left the keys in it to become an insurance problem and not his. Again speculate all day. If you want an answer you're going to have to pull it down.

 

How do you "KNOW" all the injectors are working correctly?
IDS would tell you if you are having a contrition issue.
Two tests to run under IDS Uncompensated Power Balance and Relative Compression Test.

 

You'll get a little shake, rattle, roll (often a whole lotta shakin going on) when you run these without the trans installed - perfectly normal, but you have something else going on -- I'd first check the crankshaft end play (.015-.020 (0.508 mm) tops, preferably less) , suspect (like you) it has a bearing, out of round or other mechanical, structural integrity issue. The fact you had oil leaks back there is supporting evidence - ALL Powerstrokes over time show hardened/worn rear seals and some leakage, but if accompanied by excessive metal on metal noise as described, then it's certainly something lower end integrity related.