The engine is quite nice to work on (having rebuilt my JTD mjet) , cam belt is quite easy to do along with the aux belt.
They can make 200hp+ without any high spec rebuilds, and still return 50+mpg easily.
The major thing to watch out for is an overdue cam belt
change, they seem to fail way before the due date. Change along with the water pump
, as the bearings in the pump are rubbish and wear very quickly and can seize leading to belt failure.
Mine is the 140ps spec (M-Jet before JTDm) my average mpg since new MAF and resetting my ecu is 63mpg (~500+miles), failing MAF causes all sorts of wierd engine running, no power under 2krpm, smokey on WOT..
EGR valve is a common problem (recirculates exhaust gas ro reduce NOx emissions) This valve soots up and jams part open causing poor running ect, but easy diy dissassemble and clean.
So far I love the JTD 16v engine.
I want one for my kitcar!