Kubota engine rebuild problem

[jimd333]

The engine is a two cylinder diesel (Z500).
It's forty years old and has been rebuilt before.
I recently changed the piston rings. On startup, the engine lit off and immediately seized. I was told by Kubota that the connecting rod cap bolts are YTT ( yield to torque) bolts and shouldn't be reused as these were used at least two times before.
I removed the end caps and found no metal or damage, and while the crankshaft now turns, I believe the number 1 piston is hitting the cylinder head.
I was hoping not to have to remove the cylinder head again. Has anyone experienced a "spun bearing " before?

 

[ROUSTABOUT]

Removed end caps or rod caps? If it was rod caps, you'd see the bearing problem right then. Are the Pistons turned the right way? Are the rod caps? I mark everything before I take it down. Are the rod caps on the rod they came off of?

 

[jimd333]

Yes, rod caps is what I meant. It's too late to mark now, but I was working with a flashlight last evening. The number stamps on rod caps looked to be properly oriented with the rod.
What should I look for next? Should the bearing be replaced? Can I get this done without removing the cylinder head? Thank you.

 

[ruffdog]

I removed the end caps and found no metal or damage, and while the crankshaft now turns, I believe the number 1 piston is hitting the cylinder head.

Is the piston hitting the head or a valve? Is there an foreign object smashed between the head and piston?

 

[Tinhack]

Is the piston hitting the head or a valve? Is there an foreign object smashed between the head and piston?

Yep, they don't stop on their own.

I have the same engine in my Kenbota. It started life as a G3200 lawnmower with 1300+ hours. It's still running strong. The only thing I did was clean it, paint it and changed to a "real" alternator. It's no longer a lawnmower.

 

[jimd333]

Is the piston hitting the head or a valve? Is there an foreign object smashed between the head and piston

Yes, the valve is being struck. I have very limited time to work on this, but will check in soon. Of course, everything is out of sequence! Thanks.

 

[alexpops]

Timing marks lined up? New valve springs? Pushrods/rockers in same places? Pistons in the same orientation? Lash set? What changed other than the rings?