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Your Crankshaft worn out? » Read more about common malfunctions • Repair • Replacement manual
Pacing the engine with the crankshaft
The crankshaft is the crucial component, which converts the linear movement of the piston into a rotational movement. It is located deep inside the engine block. Its replacement is tantamount to a major engine rebuild.
Crankshaft operating principle
The crankshaft is a one-piece rod provided with a sturdy step profile. The connecting rods are attached to the individual indentations, which are in turn bolted to the pistons in the cylinders. An engine always has just one crankshaft, regardless of how many cylinder banks it has. The crankshaft protrudes from the engine block, at least in the direction of the clutch. This is the point at which the force produced in the cylinder is converted into usable rotary motion. The shaft is used to control the camshaft and to drive auxiliary units. For this, it is either equipped with an internal gear to which a timing chain is attached. Alternatively, the motor can be controlled by a timing belt. In this case, the camshaft protrudes from the engine block on both sides. Also, a pulley is attached to the crankshaft in this case. The double-sided sealing is achieved by shaft seals. The units driven by the shaft are the generator, power steering pump, oil pump, water pump and the cooling compressor. This is usually done by toothed belts.
Fortunately, damage to the crankshaft is very rare. The shaft can become ground down at all points of contact or completely break due to material fatigue. Crankshaft damage is typically caused by material fatigue or a lack of lubrication.
However, an engine is designed in such a way, that bearings on the connecting rod and main bearings will fail first. This will become noticeable through a rough run and strong vibrations. However, if a crankshaft does break, a total destruction of the engine is usually inevitable. The great forces break through the housing and distort the overall architecture of the engine in such a way, that a complete replacement is the only option.
A simple yet slightly expensive trick can provide accurate information as to whether a crankshaft can be expected to break soon: The bearing shells of the connecting rod and main bearings generally consist of sintered bronze. An analysis of a sample of the oil allows for exact determination of whether abrasion dust from the bearings is contained. If the bearings are heavily worn, the shaft will also be affected soon. A previous overhaul of the bearings can prevent this damage and make for a much cheaper repair. An analysis of motor oil costs about 50 euro. Replacement of the crankshaft A crankshaft repair is very expensive. This repair is easiest to perform on standing in-line engines. For this, the oil is drained and the oil pan removed. The main bearings and connecting rod bearings are loosened, whereupon the crankshaft can be pulled out in a downward direction. A new crankshaft must be ground in and balanced, otherwise it will end up being destroyed again by its own strong momentum. Since the pistons are easily accessible when removing the crankshaft, this is a good opportunity to change the piston rings. With this quick and inexpensive measure, the creeping loss of compression is effectively prevented. Of course, you should also examine the piston's tracks for scoring when performing this work. The replacement of crankshafts is also a popular tuning measure. A modification of the tilt angle can improve engine performance under certain circumstances and in conjunction with other measures. However, this task should only be performed by outstanding engine specialists. Crankshaft quality through use of original parts Next to the cylinder head, crankshafts are the most highly stressed component in an engine. Their manufacture is precision work, especially in terms of their subsequent treatment in the form of grinding and balancing. Most commonly, crankshafts for mopeds and motorcycles require replacement. These have to withstand much higher speeds than cars, which leads to faster wear. A car's crankshaft usually costs several hundred euro.