I have just pulled apart the TZi engine, my first XU.
Cetainly not in as good a condition as an XN motor of the same age, bearings look pretty worn and crank has a dull look although no scoring.
Interesting also to see the old style cast iron oil control rings.
One thing that really stands out though is the weight of the con rods, surely light weight rods would give a good benefit, has anyone investigated this?