Diesel engine overhaul costs a fortune

MOTORING

Overhauling a petrol engine is not as costly as a diesel engine because its manufacturing costs in terms of the materials used are much lower.

This is not so with a diesel engine. Daniel Katumba a senior mechanic in Rubaga says diesel engines operate at a slightly higher temperature and are mostly used for heavier work.

Though due to recent advances in technology they are now employed in salons and medium commercial vehicles.

He says diesel engines need to be more robust than petrol engines because they encounter higher cylinder pressures.

The principal parts affected are cylinder block, and crank case cylinder head, pistons gudgeon pin, connecting rod crank shaft and main and big end bearings.

Making the parts heavier and more robust causes greater frictional and inertia losses and, hence an increase in fuel consumption and slower acceleration. It also means using more expensive construction materials.

Pistons may be made from cast, Iron or a cast iron body may be used in conjunction with a steel heat-resisting crown, but the majority of engine manufacturers prefer an aluminum alloy.

Henry Mivule another mechanic in Matugga says the piston is sturdier than its counterpart in the petrol engine because of the high pressures.  It tends to be longer particularly when the crown has a cavity or toroidal recess.

Mivule says the connecting rod is made out of high-tensile alloy steel such as manganese molybdenum. Crankshafts of the diesel engines are made from high-tensile steel alloys like chromium molybdenum.

According to Mivule main bearings are made from lead, bronze or copper. Lead steel backed bearing shells give the required degree of hardness and plasticity and yet have a high load carrying capacity.

Due to the high manufacturing cost, this also affects the cost of square parts for a diesel engine.

For instance, overhauling an engine model diesel of 3L (this is common in the commuter Hiaces and Hiluxes) will cost one about sh700,000 to sh1.2m (in buying the necessary requirements for the overhaul).

Katumba says diesel engines are very economical in terms of fuel saving to distance covered, and can serve faithfully in their span, but if it comes to engine overhaul you really have to spend money for quality work.

He says it is not advisable to do a partial overhaul on the diesel engine. For better performance and longer service life, full overhaul, including phasing and calibration operations on the injector pump and the injectors, is necessary.

Do not expect to overhaul your diesel engine at the same cost of the petrol engine. Normally it costs twice as much.

It is advisable to always resleeve your diesel engine to standard size for longer service life especially the 2L and 3L which are so common in Uganda today.

Engines that are resleeved but overhauled will within a short time behave as though overhaul was not done.