Diesel injector pump problem

[Pinchers]

Ok well my truck developed a fault at the weekend, I was driving with no problems and stoped the engine, When I went to start the truck up again about an hour later, it turned over and ran with a lumpy/coughing idle, reduced power, blue smoke. It had all the same symptoms of a problem i had a wee while ago. I thought i would get stuck in and just take the pump out before trying the more easier options first. Ive just had the delight of stripping out the fuel pump in the dark and cold to discover i have sheared my second drive shaft on the pump...

See pics below, the one on the right is the one i just removed. There is no more than 500miles between the pump being swapped. When i fitted the last pump everything was torqued up acording to the workshop manual. The truck was running well with no problems.

Can anyone give me any ideas why i have now sheared two drive shafts?before i fit my 3rd pump.

[wishbone]

Maybe check the idler gear behind the timing case cover has been installed properly - it has a pair of 'sprung' thin gears attatched to it that have to be pre-tensioned before installing.

Also there should be a bit of endfloat on the pump pully. Did you check it was within tolerance (0.15 - 0.55mm) ?

Edit: Remembered today there's a bearing on the pump drive gear too - maybe thats seized ?