The crankshaft is the central part of not only the engine, but the entire car. The name itself speaks of its form. Now a little about his appointment. In places of the knees, it has necks, on which the connecting rods are fixed with the help of caps, drawn by bolts. During the stroke of the piston, the energy that exerts pressure on it is transmitted to the knee, and, through the lever, rotates the crankshaft around its axis.
The moment that is on the crankshaft in order to crank it up a full revolution is called the torque. Engines that have the same volume and different number of cylinders have different torque, it is not difficult to guess which one will have more.
The crankshaft speed can reach 8 thousand, so the load on it is very high, and the friction force is also great. To facilitate working conditions, as well as reduce the very friction force, a lubrication system is used, moreover, under pressure. We will not affect it in detail and consider other shafts, we will only say that the system itself is under pressure. In order to reduce wear and delay the repair of the crankshaft, liners are made between the lower head of the connecting rod and the neck of the crankshaft, which are made of softer metal than the crankshaft itself.
Between the liners and the neck a film is formed, a few microns thick, which serves as a lubricant and improves the rotation glide.
The main engine malfunction, when it may be necessary to grind the crankshaft, is the pressure drop in the lubrication system when grooves appear on it. Of course, this may not be the case at all, but, for example, an oil pump, but this is the most common malfunction.
Before deciding which method to eliminate it, it is worthwhile to measure the necks, both the main ones (they are fixed in the engine block) and the connecting rods (connecting rods are fixed on them). Measurements should be made two, perpendicular to each other. If the deviation from the nominal neck size is more than 0.05 mm, then the crankshaft is ground. Naturally, this is done by professionals on high-precision equipment.
After grinding on the flywheels of the crankshaft, a repair-size index is stamped, each of which corresponds to a letter, it is for it that it is worth choosing liners. Typically, the crankshaft has three repair sizes that exceed the nominal in increments of 0.25 mm.
But things may not be so complicated. If the wear does not exceed the specified, then you can limit yourself to replacing the liners. They can be the same size as the previous ones, or one size larger. The second case is applicable only if the wear of the necks is uniform, without furrows and channels, since it is precisely because of their appearance that the pressure in the lubrication system drops.
From the foregoing, it is worth making one simple, but very important conclusion. The pressure in the lubrication system must be constantly maintained. If it is not there, then the crankshaft will receive severe wear, it will be overheated, and with it the lower connecting rod heads. After they will have to be replaced, and this is a very expensive repair, not comparable to grinding the necks. In addition, the camshaft of the gas distribution mechanism is lubricated under pressure , and even more than one. If the pressure drops throughout the system, then the camshaft will also not be left without damage, and this is even more expensive.