Howdy folks. Got another mess that I'm hoping to pick your brains on.

Engine is out of an 83 300SD. When cold it's mostly fine, as it warms up there's a vibration that is very obviously matched to engine RPM. Rises as I accelerate through a gear and goes back down when I shift, then rises again with the next gear. Idle I notice no difference, revving while sitting I notice no difference. With the clutch engaged and drivetrain loaded, either on the throttle or coasting down using engine braking, there's significant vibration. Put in the clutch and let the engine idle while the vehicle is still moving and in gear, vibration goes away. Power is good, throttle response is good, no unusual noises. None of this for the last 16k miles.

No inspection port to check out the clutch/flywheel, which would be my preference at this point. Considering dropping the transmission this weekend, unless one of you says "nope that's classic rod bearing behavior". Have a lot going on and will probably have to wait on any of this until after the move. At least then I'll have a nice shop to work in.

Thanks everyone.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap