Tension spring? W124 250TD

[MB250TD]

My W124 250TD (5 cylinder non turbo diesel estate) is producing some white smoke on acceleration, and at idle there is a new, although barely detectable rattle just behind the radiator. Might this be a broken tension spring? A well informed colleague suggested that it might be from the sound. If so, does anyone have an idea of how big a job is this to put right?
Thanks for your help.

 

[Dieselman]

Difficult to say.
If the rattle is heavy then it may be the timing chain tensioner which could be checked by checking for a slack chain.
The white smoke is more indicative of incomplete combustion. Check the head gasket is good.
It could be that the advance mechanism has a broken spring but that would cause the timing to be very advanced so would cause knocking especially at idle.

 

[MB250TD]

Thanks Dieselman,
The head gasket is fine. The car runs fine, and white smoke does not last when warmed up. It does idle more erratically than normal and makes more knocking noises than normal. Maybe the advance mechanism broken spring idea is in the right direction. Is this a big job?
Thanks

 

[Dieselman]

Remove the vacuum pump from the front of the engine and have a look. To remove the advance mechanism you will need to set the engine to TDC and remove the chain tensioner.
You will need to hold the chain in position while the mechanism is off the car.

Having re read your previous post are you sure this sin't either a bad injector or duff glowplug?