Please dont use my cam chain experiences to judge the cam chain job on these engines. it is MORE WORK than a petrol cam belt but it's not THAT bad.
Drain the oil
Remove gearbox brace frame and remove sump pan all easy access (ish). Biggest annoyance will be the exhaust pipe.
Clean and degrease the sump pan with rags and cheek for metal bits. Mine had a few tiny needle rollers. They are from worn out valve rockers.
Remove all four glow plugs.
Lock the crank (9mm pin into flywheel from front of engine).
Remove the crank end bolt (left and thread and
VERY tight). The timing is now screwed. Leave that pin in place and DO NOT TURN THE ENGINE. Put gaffa tape over it.
Support engine on scrap wood blocks and a jack. It's a clever beast because the bottom half main bearings are held in a single aluminium casting. Just avoid bending the windage cover.
Remove engine mount and its bracket to the engine block.
Remove cam chain/oil pump cover bolts and remove the cover. It comes out complete with oil pickup tube and strainer.
Clean the gasket face on engine side.
Use a holding tool into the cam sprocket to brace against while loosening the end bolt (normal thread).
Remove cam sprocket, crank sprocket, pulley hub, chain tensioner, chain guides and oil spray bar. All to be replaced.
Fit the new parts - cam sprocket, crank sprocket, pulley hub, chain tensioner, chain guides and oil spray bar. All to be replaced. Chain is free to rotate.
Tighten the cam sprocket bolt (not replaced). Use the same tool to hold it while torquing the bolt (torques are way back in this thread).
Pull the tensioner retaining pin to tension the chain.
You now have what should looks like a complete new cam chain kit but the crank sprocket is still free to turn.
Check the crank is still locked. Lock the cam using a FIRE engine cam lock. You could use two but the cams are geared together 1-to-1.
Fit a new oil seal to the cam chain cover. I had to drill the seal and use a wood screw and prybar to get mine out.
Check the head to block joint lines up flat. It it's slightly stepped (as mine was) apply some silicone instant gasket to the low side.
Ensure cover joint face is clean and refit using the new gasket. It has tube dowels so can't be fitted out of line. Fit all of the screws.
Insert the NEW belt pulley hub. Some kits dont include one. Part number is 73500417 (per forum
ePER).
Fit the new LH thread bolt and torque to 240 Nm though the GM standard is 150 plus 90 degrees. It's a heck of a load but the crank timing pin is at flywheel radius so has some leverage compared to a centre mounted lock tool.
Remove both lock tools and VERY carefully turn the engine 2 full turns. There's no compression so should be smooth.
Reassemble everything else. I used Loctite instant gasket on the sump joint face.
The sump pan is dirt cheap so if it's rusty just replace. I've primed and painted mine. I also used large head stainless socket screws to refit the cover as they are easy to fit and low cost. A dab of sealant under the head flanges avoids galvanic corrosion.