How to find out your finger size for a ring - ring size chart

The crankshaft (crankshaft) is an important component in the crank mechanism of a car. Its function is to sense the reciprocating motion of the pistons and convert it into torque, thus ensuring smooth engine operation. Structurally, it consists of several main and connecting rod journals connected to each other by cheeks. As wear occurs, the shaft is ground to repair dimensions, which accordingly changes the dimensions of the crankshaft journals. Usually up to 6 repair sizes are provided; Soviet standards allowed 8 for a number of models.

What are the repair dimensions of crankshafts for? - AutoDoza - Automotive portal

The crankshaft is made of either cast iron or alloy steel; both materials are quite strong, but defects still arise over time, and repair dimensions of the crankshafts are needed to eliminate them.
These are peculiar tolerances to which the thickness of the necks can be reduced without severely compromising the strength of the part. And, since the journals usually interact with the bearings, the latter are provided with liners with repair reduction. First of all, let's look at the different types of defects that occur, as well as the reasons for their occurrence. If the geometry of the seats for the support bearings of the block is broken, rapid wear of the journals should be expected. In other words, if this process is observed, the reason is most likely exactly the same as indicated above, or in the poor quality of the material of the shaft itself. Due to poor-quality oil or its irregular replacement, scuffs may appear on the necks; a clogged oil filter, or, which is even worse, low pressure in the system, can also be the source of this trouble.

There are two types of crankshaft journals - support and connecting rod. The latter, as the name implies, are designed to transmit the translational movements of the connecting rod to the knees, thus transforming them into torque. In essence, this is the principle of a well gate, or more precisely, its curved handle, in relation to which the human forearm can be considered a connecting rod. In a standard engine, the dimensions of the crankshaft journals correspond to 47.8 millimeters. It is logical that both the bearings and connecting rod rings are also adjusted to this size. However, the sports type of crankshaft is an exception; its journals have a diameter of only 43 millimeters, which means it requires special bearing shells and the installation of appropriate connecting rods.

When you are planning to grind the shaft journals, take care of the inserts in advance; during the first repair, they can be used with a reduction of 0.25 millimeters. If necessary, subsequent repair dimensions of the crankshaft journals can be changed to 0.5, 0.75 and 1 millimeter; the corresponding liners must also be purchased. Subsequent grinding is associated with a direct risk of shaft destruction during operation; for this reason, liner sizes 1.25 and 1.5 are extremely difficult to find.

How the crankshaft is bored

Let's start with the fact that boring and grinding a crankshaft with your own hands in a garage can only be done by experienced specialists who have the appropriate set of special equipment. First of all, a crankshaft boring machine must be available, since the entire procedure must be carried out with high precision. It is also necessary to take into account that the complexity of further adjustment of the repair liners will directly depend on the quality of work on the crankshaft.

Also, some car enthusiasts, in order to maximize savings, manage to grind the crankshaft in the garage with improvised means, but this procedure is strongly not recommended, since the result can be completely unpredictable.

Let us add that before starting work, a specialist must check the crankshaft for axial displacement of the connecting rod journals, bending of the crankshaft, etc. At the same time, it still turns out that although shaft repair is a complex turning operation, buying a new part will still be on average 50-60% more expensive compared to how much it costs to bore a crankshaft by an experienced craftsman.

KamAZ 740 crankshaft, Characteristics of the KamAZ 740 crankshaft and repair dimensions.

Peugeot 405 1.6 XU5JP Logbook New piston rings and repair of crankshaft thrust half-rings
The KamAZ 740 crankshaft is made of high-carbon steel by hot stamping and is also strengthened by nitriding or hardening with high frequency currents (HFC). The connecting rod and main journals are subjected to hardening. The KamAZ 740 crankshaft has four connecting rod journals and five main bearings that connect the jaws. The crankpins of the shaft are made in such a way that they have cavities inside that are closed with plugs. The cavities are designed for additional oil purification through centrifugal forces.

To balance the centrifugal forces, counterweights are installed on the so-called nose (the front end of the crankshaft) and the shank (the rear end of the crankshaft), which on the cheeks are integral with the shaft, and are pressed onto the nose at the time of assembly and secured using a segment key.

The oil pump drive gear is fixed at the front end of the crankshaft; it is the drive gear, and at the shank (rear end) there is a distribution gear with an oil deflector. In the front part (nose) of the crankshaft there are holes used for installing the coupling half. In the front part of the shank there are two holes intended for pressing in the pins securing the flywheel, an axial hole for the support bearing of the gearbox input shaft and threaded holes for the flywheel mounting bolts.

The possibility of axial displacements is eliminated by fixing the shaft using four thrust steel-aluminum half-rings, which are installed in the recesses of the engine crankcase and the main support cover. On the rear part (on the shank), the crankshaft is sealed with an oil seal pressed into the flywheel housing.

The role of connecting rod and main bearings is performed by the liner, which are installed in the so-called beds. Both main and connecting rod bearings are made of steel strip, which is coated with a layer of lead bronze. In the main bearings, the upper and lower parts are not interchangeable, since the upper parts have holes for supplying oil and grooves for distributing it. But the halves of the connecting rod bearings are interchangeable.

During engine operation, the KamAZ crankshaft journals wear out, and it is allowed to be ground four times, and the liners are available in seven repair sizes.

But another feature of the KamAZ crankshaft is that the block and connecting rods can also be bored to size.

Repair dimensions of crankshaft journals and bearing beds

Marks of the repair size and diameters of the crankshaft journals and beds in the block or connecting rod are applied to the back side of the liner not far from the parting plane.

The flywheel (Fig. 2) is necessary to accumulate kinetic energy during the power stroke and rotation of the crankshaft during auxiliary strokes, as well as to remove the piston from dead points and reduce the unevenness of shaft rotation.

The flywheel is cast from special gray cast iron. It is secured to the rear end of the crankshaft with eight bolts 3 made of alloy steel. Precise fixation of the flywheel on the crankshaft is achieved using two locating pins pressed into the end of the crankshaft. A ring gear 1 is pressed onto the machined cylindrical surface of the flywheel, intended for connection with the starter shaft gear when starting the engine. The clutch is installed at the rear end of the flywheel. To regulate the engine, there is a groove on the flywheel for flywheel lock 2 and 12 holes for turning the crankshaft with a crowbar.

Engine malfunction

Naturally, the connecting rod and crankshaft became unusable. The photograph clearly shows longitudinal cracks on the connecting rod journal of the crankshaft.

Upon closer examination, the main reason why the engine failed was discovered. On the connecting rod of the third cylinder there was a connecting rod cap of the second cylinder, and on the connecting rod of the second cylinder there was a connecting rod cap of the third. Again, strangely, the crankshaft should jam immediately when tightening, but apparently the covers matched each other.

And so I had to change two connecting rods and the crankshaft. They did not disassemble the cylinder head. The valves on the head were in good condition at the last overhaul, ground in, and the oil seals were also replaced. This engine has a weakness; the studs, with the help of which the camshafts are attracted in bed, are easily pulled out of the threads. Which leads to additional costs.

Installing the crankshaft

After the parts were washed from dirt and used oil, assembly began. First of all, we install the crankshaft, having previously installed the main bearings.

After installation, the bearings must be lubricated with engine oil. Which you will use in the future. Don't forget, the earbuds have locks. They are inserted into specially provided grooves in the block bed. In addition, there is a peculiarity of modern earbuds: they come in different sets. Half of them have a lobe groove. To supply oil to the crankshaft journals. We install them in the engine block. Inserts that do not have grooves are installed in the main covers. Before installing the covers, it is necessary to install axial displacement half-rings. There are grooves for them in the engine block on the bed of the third main journal. We install the half rings in such a way that the side intended for sliding is directed towards the crankshaft. This side has a characteristic coating and channels for lubricant.

Then we tighten the covers with bolts. Here, under no circumstances should the covers be mixed up, and also the liners installed in the block and the main covers must be positioned lock to lock. This is very important, as a mistake will lead to immediate, costly failure or the shaft will simply jam when tightened. Repairing a VAZ 2112 engine is not very difficult, but simple mistakes due to inattention lead to disastrous results, as in our case.

All covers must be tightened evenly, in several stages; it is very important that the loads on the main journals of the crankshaft during tightening are distributed evenly, because this will prevent damage to the shaft itself and the liners. The final tightening of the covers must be done using a torque wrench with a force of 66.31-84.38 N*m .

After tightening, we turn the crankshaft; it should rotate freely by hand, turn it several times, the resistance exerted by the shaft during rotation should be uniform without biting or braking, if this is not the case, then you need to look for the problem.

The essence of the problem with ring sizes on Aliexpress

VAZ 2109 hood size

Considering that Aliexpress is an international platform and sells its goods in the Russian Federation, the USA, and Europe, the sizing charts of goods must comply with regional standards. The question arises - what ring size is indicated in the lot, in what international standard? And how can we convert this size into one that is familiar to us, buyers from Russia?

An additional complication stems from the traditional Chinese laissez-faire attitude toward the characteristics of their products. Especially if the product is not expensive, such as rings not made of precious metals. How to find out the exact ring size, not plus or minus a centimeter?

What are the sizes of rings in general (and what is the difference)

In Russia, the indicated ring size is its internal diameter in millimeters.

In Europe there are several internal standards, but now in most stores you can find out the size as the length of the inner circumference in the same millimeters. Accordingly, the European size is easily recognizable in the lot on Aliexpress. European size starts with numbers around 40 mm, and Russian ring sizes are numbers from 14 to 22. And it is easy to recalculate, ring circumference (European size) = 3.14*ring diameter (Russian size).

The situation is worse with English, American and Japanese ring sizes. The British generally use the letters of their alphabet to designate ring sizes. As a result, there is not enough mathematics to translate these dimensions. Ring size tables are used to determine compliance. They are not difficult to find on the Internet and we won’t bother you with it here. Let us present only one short table.

How to correctly determine ring sizes on Aliexpress.

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Ring sizes on Aliexpress for all sellers without exception are expressed in the American measurement system.

In order to choose the right ring size for yourself, you need to look at the ring size correspondence table offered by the seller in the product card. If you know your standard Russian ring size, then a simple and clear size table will tell you whether it corresponds to the American size. To do this, just select the Russian size, which is equal to the circumference of the finger in mm.

Otherwise, buyer will have to measure the finger circumference by themselves as shown in the pictures. The images may differ from one seller to another, but the procedure itself remains the same. You need to take a piece of thread or a narrow strip of paper and wrap it around your finger. Next, you should mark the circumference of your finger with a marker and lay a thread or paper with a mark to the ruler. Substitute the resulting number in mm into the table and determine the correct ring size.

What should you pay attention to when independently measuring your finger circumference? On the shape of your own fingers and the quite logical difference in the methods of measuring ring size in different Aliexpress stores. One Chinese store may offer to measure the circumference of the finger joint, another - the circumference of the phalanx under the finger

It’s better to take measurements of both, and then choose the greatest result. Otherwise, the purchased ring will either not fit on your finger, or it will be very difficult to remove.

By the way, the table of ring sizing charts from different sellers is slightly different. There's nothing to be done, China is China. Therefore, in order to determine your ring size, you can either choose the average value of ring size indicators, or use the grid offered by a specific seller.

Buying different types of rings requires an individual approach. It's good if your choice is a ring with a changeable size. Then you won’t have to fool yourself with determining the correct size, but simply bend the rim of the ring a little.

And when buying a Chinese copy of a very original Cartier Trinity triple engagement ring, you will have to choose one size larger than yours. This is required by the design features of the ring - three thin bands of yellow, white and pink colors are connected to each other in a special way. Each ring individually may fit you perfectly, but the rings that fit into each other will be too small for you because of this connection. In order to freely put on and take off such a ring without feeling discomfort, an additional size is required.

Before you finally decide on the size and choose a ring, you should also read customer reviews and, just in case, consult with the seller about the correspondence of the size chart to the actual dimensions of the product.

https://youtube.com/watch?v=PYg0aKo4k8k

Assembly of the crankshaft with bearings after repair

The shaft journal-bearing assembly is assembled on the principle of complete interchangeability.

To ensure complete interchangeability of parts of an assembly unit, during manufacture or restoration it is necessary to process both the crankshaft journal and the bearing with certain accuracy standards that determine the tolerance range of the parts.

If, when processing a batch of parts with a tool configured for size, deviations from size are formed under the influence of a large number of independent or weakly dependent random factors, then their distribution curve corresponds to the normal law or the Gaussian curve. For the normal distribution law, from the conditions of complete interchangeability, the tolerance is taken equal to ±3 σ

, i.e.
6 σ
(
σ
– standard deviation).

Table 5.1

Initial data for assembly calculations

crankshaft with bearings

Let us determine the number of crankshaft journals in a batch of 200 pieces, the deviations of which are within ±2.5 σ

:

From Table 6.1 we find that Ф

(2.5) = 0.09275, and since the Gaussian curve is symmetrical with respect to the arithmetic mean size, then 2
Ф
(2.5) = 0.1855. It follows that 86.64% of the necks have specified deviation limits.

Their number will be equal to:

Tolerance for neck processing:

Since the curve is symmetrical, the arithmetic mean is:

Deviation values ​​for the diameter of parts are within ±1.5 σ

:

Thus, 37 parts from a batch of 200 pieces will have dimensions within

with a tolerance of 0.02 mm.

Maximum deviations of the bearing diameter, ensuring the assembly of the unit according to the principle of complete interchangeability:

EI

and
ei
– lower limit deviations of the bearing and shaft journal, mm;

ES

and
es
– upper limit deviations of the bearing and shaft journal, mm;

Smax ( M ) _

and
S min ( M )
– maximum and minimum values ​​of the installation gap, mm;

Arithmetic mean diameter:

Standard deviation:

Distribution coefficient:

Integral value:

From Table 6.1 we find that Ф(К 1 )

=0.2257, and
Ф(К 2 )
=0.4641.

Subtraction gives the relative number of parts in a batch with deviations from K1 to K2.

Number of bearings that provide the required assembly conditions with the shaft journals:

.

VAZ 2108 engine repair

We repair the VAZ 2108 engine after disassembling the engine, cleaning, washing and drying all the elements.

1. Clean the piston head from carbon deposits. The piston should be replaced if there are burrs, burnouts, deep scratches, or cracks on it.

2. Use a piece of wire to make holes for oil drainage.

3. Adjust, if necessary, the gaps between the rings and grooves on the piston.

4. Measure the gaps in the piston ring locks using a piston ring inserted into a special mandrel. The nominal clearance of the PC is 0.25-0.45 mm, as a result of wear, -1.0 mm is permissible. If the gap does not fall within these values, replace the PC.

5. If the gap is less than 0.25 mm, grind off the ends of the PC with a file.

6. Measure the gaps between the pistons and cylinders. The nominal gap is 0.025-0.045 mm, permissible - 0.15 mm. If the gap is greater than 0.15 mm, bore the cylinders and install pistons of the required size. Measure.

Characteristics of crankshafts

Characteristics of crankshafts photo, Instructions for engine modification, engine tuning

Of course, it is difficult to single out any of the most important parts in a car, but the crankshaft can be considered one of the most important, because it is the one that converts the forces from the pistons and connecting rods into torque, which moves the car.

In this article we will look at some parameters of crankshafts for “classics” and the features of their replacement and installation.

So, “classic” crankshafts have several parameters that may differ.

1. Crankshaft stroke - the distance between the axes of the connecting rod journal at bottom dead center (BDC) and top dead center (TDC)

On classic engines, the factory installed crankshafts with a stroke of 66 mm, 80 mm and 84 mm. In addition to them, there are sports crankshafts with a piston stroke of 86 mm, 88 mm and even 90 mm. However, you should not think that by installing a crankshaft with a stroke of 90 mm in the block, the engine will immediately become much more powerful. The behavior of the engine is greatly influenced by the ratio of the length of the connecting rod and the stroke of the crankshaft - the so-called R/S. Many believe that the “golden mean” of a cylinder block is an R/S value of 1.75.

If R/S is large, then the piston remains at TDC longer, therefore more complete combustion of the fuel mixture occurs, hence greater pressure on the piston after passing TDC. The result is good torque at medium and high speeds. Also, a long connecting rod reduces its friction against the crankshaft. However, there are also disadvantages - with a long connecting rod and a short stroke, due to a decrease in air flow speed (again due to the lower piston speed after TDC), good filling of the cylinders at low and medium crankshaft speeds is not ensured. There is also a high probability of detonation due to the high temperature in the combustion chamber and the long time the piston remains at TDC.

If R/S is small, then a very good cylinder filling rate is ensured at low and medium crankshaft speeds, and also due to the short time spent at TDC (and therefore the higher piston speed at the beginning of the stroke), the mixture becomes more homogeneous, which contributes to better combustion. But there are also disadvantages here - a small R/S value means a larger angle of inclination of the connecting rod. Therefore, a large force will push the piston in a horizontal plane. Therefore, the load on the connecting rod, on the walls of the cylinder block, and the pistons of the ring increases, the operating temperature increases due to increased friction, and lubrication deteriorates. Well, due to the increased piston speed, the engine life is also reduced.

Another common problem when installing a crankshaft with a long stroke is the connecting rod touching the block wall. In this case, you need to refine the wall using a grinder or grinder.

2. Crankpin size

The crankshaft journal is a support with which the shaft is connected to the connecting rods.

The standard diameter of the connecting rod journal in a “classic” engine is 47.8 mm. The rolling bearings and connecting rods are also made to this size, however, on “sports” crankshafts with a stroke of 86 mm, 88 mm and 90 mm, the diameter of the connecting rod journal can be 43 mm. It requires special liners, as well as connecting rods, don’t forget about it!

3. Number of counterweights

Counterweights provide unloading of the main bearings from the centrifugal forces of inertia of the unbalanced masses of the crank and the lower part of the connecting rod. On standard crankshafts 2101 2103 there are only 4 counterweights, essentially on one side on the cheek (the main and connecting rod journals are connected) from the main support. On the remaining crankshafts 21213 and with a stroke of 86 mm, 88 mm, 90 mm there are already 8 of them, which ensures a more balanced unloading of the main bearings from inertial forces.

Crankshaft 2103 with four counterweights

Crankshaft 21213 with eight counterweights