Firstly, Hi to all, i'm a new member from the uk and i have a 2002 mazda 6 2.0 diesel sport. I should probably be saying this in the new members forum but i'll admit i'm a bit impatient and thought i'd save time by saying hi in the forum i'm gonna use most.

Well the main reason i'm here is because i'm after some advice about my failed crankshaft.

Back in july i purchased my mazda 6 from a dealer, after getting used to the car i realised the car had fairly bad clutch judder which after a bit of research i realised was quite common on the 2.0 diesel especially considering mine had covered 70k. However a couple of months ago this judder turned to a bad rattle/knock from the engine so i stopped driving it. The garage i bought the car from said that at the time he didn't have a mechanic so i had to source my own mechanic then claim through warranty. Well the mechanic replaced the clutch and a rather faulty dual mass flywheel and after putting it back together the car still had a bad knocking sound.
At this point, the garage i bought the car from agreed to take the car back for repair as he now had a mechanic again. His mechanic stripped the engine down to find a crack in the crankshaft on the flywheel end. He's claiming previous mechanic must have damaged the crankshaft taking off the gearbox and flywheel so is refusing to pay for repairs, whereas the original mechanic who attempted the repair claims the car went out the same as it came in so is also refusing to pay.

So as you can see i have an expensive problem. My main question is:-

From anyones expert opinion, how can a crankshaft crack/break. Could it be through driving because i've been told that's very unlikely. Or has a negligent mechanic caused me a whole lot of grief.

Any help would be much appreciated thanks.