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Working on Truck Engines


The utility vehicle diesel engine differs from the motor car diesel engine in size and in weight. There is no electric glowing, and seldom, a flame starting system. The cubic capacity is about four times higher and has, with some manufacturers, always the same displacement (e.g., 2 litres) per cylinder regardless of whether the engine has six or eight cylinders. The cylinder block is made of cast iron with replaceable wet sleeves.

How it works

In the motor car area, short engines are hardly ever repaired, crankshafts may sometimes not be exchanged at all. This is different in trucks, where the replacement of pistons and also cylinder sleeves often occurs. However, not wear and tear, but leakage, is sometimes the cause.

The coolant jackets of the sleeves are sealed to the crankcase by O rings. In this case, a defect becomes clear if when draining the engine oil, water comes out first. If one unscrews the oil sump and applies pressure to the cooling system - depending on the manufacturer, approx. 1-1.5 bar pressure - one can determine the defective cylinder. It is possible, but generally not advisable to repair only the damaged cylinder.

The removal of piston/connecting rods and sleeves is actually no problem. Due to the head gaskets usually used nowadays, the cleaning of the sleeves from above is normally successful. If this is done in the built-in state, a certain amount of grease should be applied from above onto the piston edge so that foreign particles are prevented from falling between the piston ring/-shaft and the cylinder wall. Before the removal of the cylinder sleeves, one measures the overlap on the top compared with the cylinder block at several places.

The new O rings can be also simply installed if one avoids sharp edges. Using a little grease, the sleeves are carefully re-inserted. Now, it would be nice to be able to check that the O rings have not slipped out of place. A relatively simple method of doing this, is the measuring with an inside caliper without calibrating it beforehand. It concerns after all, only small differences, with which a concave misshapen sleeve would be indicated.

If the O rings are correctly seated, the same overlap can again be observed. Sometimes rings are used afterwards, placed in an axial direction, between sleeve and cylinder to absorb vibrations. If compression rings are to be removed from the piston, the use of a piston ring expander is highly recommended. Today's piston rings, with molybdenum coating, are not as brittle as they used to be, but are at least, just as sensitive. Oil scraper rings are not quite as critical.

Professionals advise against the installation of the pistons using a squeeze-band, because the relatively sharp edged tranfer from the tool to the cylinder can lead to damage. An old wet sleeve, which at the upper end has been bevelled, to make the insertion easier, is helpful here. Before the cylinder head bolts are tightened - exactly to torque and normally an additional quarter turn-, one should consider using new bolts . Expanding-shaft bolts look like reduced-shaft bolts, however, are not as elastic. One can re-use them providing they have not yet reached a certain length. Also in this case, please follow the manufacturer's data. 10/09