STORY Technology

How do we make... a crankcase?

Posted on June 23, 2025 by Katrin Auernhammer, Images by Robert Hack

The crankcase forms has to be able to withstand immense forces. That is why it is built to tolerances of just a few hundredths of a millimeter.
Friedrichshafen, Germany

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The crankcase is the skeleton of the engine – it houses the cylinders, numerous hoses and pipes run through the component, and countless heavy engine components are attached to it. However, it not only supports the other components, it must also withstand the immense forces generated by combustion and piston movement. In addition, oil heated to over 100 degrees Celsius flows through the crankcase. Extreme pressures and temperatures are one reason why a great deal of precision is required during production to ensure that a crankcase can withstand the stresses. Tolerances of a few hundredths of a millimetre are just as important. Production requires a great deal of expertise and experience. So how is a crankcase made?

A 20-cylinder crankcase from the 4000 series weighs 2.4 tonnes in its raw state when it is delivered from the foundry. A layman might think that the crankcase is already ready for assembly. After all, it already has recesses for the cylinders. However, during assembly, it would quickly become apparent that the associated add-on parts do not fit. The crankshaft would grind, and the screws would not grip. Four production phases and four to five days of work lie between the anthracite-grey raw part and the shiny silver crankcase ready for assembly.

 

 

Milling cutters remove the skin


During this time, the crankcase passes through three machining centres. The crankcases are transported to the respective machining centre on a flexible base called a pallet. These look like large white boxes, more reminiscent of a garage or a container. But they are computer-controlled high-tech devices. The universal spindle unit is located on the side of the machine's machining area. It guides the tool over the component. Depending on the machining step, the unit automatically selects the right milling cutter or drill bit. The crankcases are then machined in seven different clamping positions: under a shower of cooling water and lubricants, tools remove chips and trim the bores to the correct diameter. To ensure that all areas can be reached, the crankcases are clamped in different positions on the pallets. ‘These devices ensure that the raw parts do not tip over, even when they are rotated by 45 or 90 degrees,’ explains Erich Fundinger, foreman for crankcase production in the 4000 series. The milling cutters and drills can take up to four hours in a single machining centre to machine large surfaces. They remove a total of 300 kg of chips. Precision is important here: the tolerances for the housings are only 0.02 millimetres deviation in the axis position from bearing to bearing for the crankshaft and camshaft bearings.

 

Milling cutters machine the blank casting under a deluge of coolant-lubricant fluid, shaving off metal until the exact dimensions are obtained.

 

Handfinished for final inspection


As versatile as the machining centres are, they cannot do everything to make the crankcase ready for assembly. In addition to a new engine platform, employees must repeatedly intervene between the individual clamping operations, for example, to install a bearing cover. ‘The machines do a lot of the work automatically, but there is always a trained employee on hand who can intervene if a problem arises,’ says Fundinger. Experience is also necessary for deburring: employees use small milling cutters to remove unevenness from the machined edges by hand. ‘Deburring can take up to three hours,’ says Fundinger. Employees use an endoscope to inspect areas in the crankcase that cannot be seen from the outside for deburring. Dirt and chips are removed in a subsequent washing cycle. Employees use a measuring machine to technically inspect the crankcases. The machine measures all functionally critical features and checks whether the machined surfaces are within the tolerances. This is followed by a detailed visual inspection: employees examine each crankcase closely, looking for chips or other residues. Packaged in corrosion-proof packaging and fitted with sealing plugs for water channels, cylinder liners and camshaft bearings, the crankcases are temporarily stored for a few hours until they are installed in the assembly line to form a complete engine of the mtu 4000 series.

 

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