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Home of the crankshaft: the crankcase
The crankcase is the bottom part of the engine. It is followed in the vertical sense only by the oil sump. It contains the crankshaft. This component being subject to considerable forces, the construction of the crankcase must be correspondingly robust.
The five layers of the engine
An engine casing is divided into five parts:
- valve cover
- cylinder head
- cylinder block
- oil sump.
The valve cover seals the upper part of the cylinder head. The cylinder head contains the valves and the camshaft. The cylinder block contains cylinder bores with the pistons. Ultimately the crankcase carries the crankshaft with its connecting rods. The oil sump is the lubricant reservoir, sealing the engine at the bottom.
To enable safe containment of the highly strained crankshaft, the crankcase is equipped with massive bearings. They support the crankshaft at every rotation speed. At its front end the crankshaft protrudes slightly from the crankcase. The timing belt disc or the timing chain pinion is attached to its external pins. For this reason the crankcase must have a reliable sealing at this end. This is usually a high-quality O-ring containing an annular spring. High-grade engines have several consecutive O-rings installed.
The crankcase is definitely not a wear part. The only thing that can cause it to fail, is a violent impact. This can be external though mostly occurs internally. Possible causes for a ruptured or burst crankcase are:
- piston fracture
- crankshaft fracture
- tension cracks due to overheating
- the underbody hitting an obstacle
A defective crankcase generally means extensive engine damage. It is noticed by sudden engine failure and massive loss of oil.
A definite diagnosis should be made prior to engine repair. Oil leaking from the crankcase does not necessarily mean a crack. Usually it is only a clogged engine ventilation. This is a hose, connecting the crankshaft with the valve cover. If this cause has been excluded, several other options remain. The replacement of a crankcase is synonymous with a complete engine overhaul. Theoretically it is possible to replace the crankcase of an installed engine, though not recommended. Complete disassembly of the engine makes the work a lot easier. It allows a total inspection for other damage and its simultaneous repair. First, the cause for the crack in the crankcase must be determined. If it is a tension crack as a result of an overheated engine, you should consider yourself lucky. Once the crankshaft or a connecting rod is fractured and has penetrated the crankcase hull, the repair becomes much more complicated. Therefore ideally the entire engine is disassembled. Cylinder head and valves should be replaced or overhauled on this occasion. When the engine is completely removed from the car, these repairs are easily and quickly done. This occasion should therefore be taken most advantage of. Installing a new crankcase implies at least new bearing cups for the crankshaft and the pistons. This requires removing the pistons and they should additionally be equipped with new compression rings and oil scraper rings. These only cost a few bob and make the car as good as new. If you really want to do it right, use the occasion to polish and hone the cylinder bores.
Laser honing for a better life span
Honing is inserting a cross grinder in the cylinder bore. This optimalises piston lubrication. Alternatively to the traditional cross grinding there is laser honing. Small abrasions are burnt into the cylinder wall. They enhance the lubrication performance considerably. The oil consumption decreases, resulting in a longer engine mileage.
Purchasing a crankcase
The crankcase is only available at the original supplier's. The manufacture of this component with its exact fit and oil lines is very complicated and a lot of work. As a new component a crankcase costs between 300 – 500 EUR (± £270 – £450), depending on the car it is used for.