The first thing to check would be the glow plugs, 25 amp draw for each as a rough estimate (100 amps together). if you have access to a standard old test light then remove the feed wires to each plug and connect the earth lead to the positive terminal on the battery and connect to the top of the glow plug. if the light comes on the plug is dead. if the glow plugs are ok then suspect the valve clearances. NOT an easy job to adjust.
Another sneak is switch the ignition on wait for the glow plug light to go out, turn off the ignition, then turn it on again, do this two or three times before starting - if this improves the starting then replace the glow plugs.
Hope this helps, MRW
Mark
December 2010
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