That's so right!

But first before doing that I would try to look in with a borescope. Both the injectorholes and the glowplug holes are very small in diameter and you better use a model where the lens can be twisted so an average home mechanic usually doesn't have one. It' so much cheaper than taking the head off, maybe unnecesary.

Some other thoughts: camshaft sensor is needed only when starting the car and would have probably earlier, even during a long time, caused startting problems. Especially with warm engine. So this is maybe not the fault but worth mentioning. The same goes with the crank shaft sensor.

It is also possible there is a leak in the fuel system, air or internal injector leak, quite easy checks. The motor needs fuel(pressure), rpm and electricity to the injectors to be able to start. These all are relatively easy to check. But I suppose the people working on the car have already made these checks..... And I really assume it is made sure the car battery is in good shape also. The starter can't do it's job if it isn't feeded with healthy power. 50 rpm too low and the ecu says no! CRD is a very demanding car in this aspect.

 

If the car was only cranked and the belt jumped, I doubt there is damage to the valves. People have been driving these crd's with damaged rockers. The knocking noise is something a person with their right mind should not do, but the car starts and runs with a pair of cracked rockers!

So when the car was cranked and it didn't start there should have been a very markable rattle and knocking audible.

The car starts with atleast echaustecha two cogs off. Smokes and makes rough noise from exhaust, but starts and runs. Cranking and not starting, no strange noises, valve damage... I doubt!

I would take a look inside with a borescope (with twisting lens tip) before taking the engine apart or getting rid of the car.

 

Simon in his first post writed something about the belt change was done "timing marks checked" or something like that. It is probably not anyway related to this starting problem, but just by saying the valves are bent makes me thinking...

The car has two timing marks, atleast the IV versions: on the high pressure pump and on the crankshaft pulley. Maybe he was quoting his mechanic inaccuratelly, but I just want to ask and make clear the mechanic is familiar with this VM engine. You can change the belt without removing the bolts on the camshafts, but is it absolutely certain he had the cams locked in right position or he had the locking plate if he took off the bolts? That is something you need yo do if changing the waterpump also. It is possible to do the hole thing without the locking plate and the cam locking pins, but you have to be very, very careful with the cam positions and check every now and then if the locking pins are removed or not used at all.... It is possible! The hardest thing is the crankshaft. You need to lock it properly. The cams can easily be checked thru the locking pin holes and there is ways to tighten the cam bolts also. But you have to have the crankshaft propely secured! The timing mark on it (TDC + 90 degrees) is some what unclear to tell from the front of the engine.

So any mechanic with no experience with this kind of proscedure can easily make it just a little wrong.

 

More about the timing marks and belt change.

The belt should be removed ONLY when the camshafts and the crankshaft are in right position. And there is no way to avoid locking the crank. And it's done by the flywheel. When the downstairs is locked you can freely play with the upstairs, even if you don't have all the right tools.

There are timing marks also on the cam pulleys a but you should totally ignore them when changing the belt if you are also loosening the cam bolts for waterpump change. The marks on the pulleys can be very misleading. There is probably also old "timing marks" done with marker pen. Ignore them. Cams tend to move after the belt is removed, especially the intake cam. So you need to have the locking pins OR make sure thru the locking pin holes when assembling the belt that the they sit right. The cam ends have these notches which should be pointed towards each other. The exhaust at 3 o'clock and the intake at 9 o'clock. You just can't see them when the pulleys are in place and you can't tighten the bolts keeping the pulleys not moving, not without a proper locking tool.

The only way to keep the pulley marks positioned is to lock the pulleys with the right pulley lockig device. You can purchase it starting from $600 or maybe you can lend it from somewhere. But you probably figure out something else or just tighten the tools with impact tool and check thru the peeking holes later and turn the cams. The cams are alwas correct when the they are in the pin hole pisition. The locking pins CAN'T be used as the only tool to lock the motor when the bolts are tightened. It is even wise to remove the cam pins if you don't have a proper lockin tool available, you really don't want to bend them when inside.


​​​And when you think you're done rotate the motor by hand from the crankshaft three rounds. If the motor spins freely you can turn the key. Then check the belt tightness once more.