The difference in the design of TU3 and XU engines is negligible.
In the TU3 engine, the bearings of the main journals of the crankshaft form one single (as the lower part of the cylinder block of the axially divided crankshaft), while in the XU engine, the bearings of the main crankshaft journals are mounted separately (cylinder block indivisible). Therefore, the method of sealing the crankshaft is different.
On the TU3 engine, the valves in the cylinder head are mounted at an angle, so that the two-way valve levers protrude, while on the XU engine, the valves are installed vertically and actuated directly through the tappets.
The TU3 engine has a different oil circuit compared to the XU engines.