Why do you get blue smoke from a diesel engine?
Blue smoke from diesel generator occurs because of oil being burnt in the cylinders. It isn't normal for oil to get into the combustion chamber and so blue smoke is a sure sign that something is wrong with your engine. You should contact someone qualified to have a look at it.
What are the common causes of blue smoke from diesel generator?
As mentioned blue smoke occurs because of oil in the combustion chamber - its not supposed to be there, so just how could oil get into the combustion chamber? Lots of ways - examples would be a faulty injection pump, faulty lift pump, worn cylinders, worn piston rings, bad or valves or valve stem seals could all cause the oil to get into the cylinder and give you blue smoke.
Worn Piston Rings
In the case of the piston rings being worn the oil that lubricates the cylinders will pass past the piston rings and into the cylinder, where the heat from the diesel combustion will cause it to burn and release the blue smoke.
When your cylinders wear down, it leaves a small gap between the piton ring and the wall of the cylinder. In this case changing the piston rings wont help and you will end up with the gap remaining and oil will leak pas the piston ring into the combustion chamber where it will burn and cause blue smoke.
Fuel dilution in the oil
If the oil gets diluted with diesel, it will become thin, allowing it to pass between the piston ring and cylinder wall. This would also apply if oil had been added to the fuel system accidentally and the diesel was contaminated with oil.
Bad Valve Stem Seals
Bad or damaged valve stem seals will cause the engine to suck oil down the valve guide into the cylinder. Again in the cylinder the oil will combust and cause the blue smoke to be emitted from the engine exhaust.