19887.3IDI
Registered User
This says a lot right here: "that came with the engine from jasper" Being a production line rebuilder they have a reputation for things that work but cause issues like this. For one thing the rods came from a pile of rods, not from one engine. And they have been caught boring cylinders different sizes. So it could be you can't solve it without a teardown.
On another note my 6.9 was rebuilt by me, and the only thing that didn't get done was balancing. It has this exact shake you are describing and I have been through everything. It has been sitting around with 3,000 miles on it but I have done everything short of tearing it down again and it still does it.
I checked all the pistons while I had the heads off and they all said .040 on them and .040 was stamped on both sides of the block. It does kind of seem like a balance issue. If I disconnect the fuel shut off solenoid and have a helper crank the engine over while I hold my hand to the exhaust it feels even then.
What about a torque converter could that cause this? Would it hurt anything if I unbolted the trans and start the engine to see if that is the cause?