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Vitaliy VOLOKITIN, test engineer of the AvtoVAZ engine tuning department, answers questions from readers.

Tell us in more detail how to correctly replace the pistons in the VAZ 2103 engine with pistons from the VAZ 2108 to operate on AI-80 gasoline.

Indeed, by installing VAZ 2108 pistons in a VAZ 2103 engine, you will reduce the compression ratio so that the engine can run on gasoline

A-76, AI-80. The mounting gap between the piston and the cylinder mirror should be within 0.025–0.045 mm, as in the 2108. When assembling all Samar and Lada engines at the factory, piston pins from the VAZ 2121 3 engine are now used - we recommend them in your case.

However, with such an alteration, the detonation characteristics of the engine will change and for the complete optimization of the combustion process, another adjustment of the centrifugal ignition controller will be required, in particular special springs. Unfortunately, we cannot offer simple ways to make them at home, and you are unlikely to find them on sale.

It follows that the resource of the converted engine will depend not only on the build quality, but also on how correctly you will be able to choose the installation ignition timing. Keep in mind that engine power with a reduced compression ratio will decrease slightly, and fuel consumption, all other things being equal, will become slightly larger.

Two years ago I bought a new re-export VAZ 2105 3. I didn’t receive any technical documentation and at first I went perfectly to the AI-92. After 30 thousand, the engine began to junk: the saddle of one of the valves burned out. Then they paid attention to the fact that the pistons in the TDC do not reach 2.2 mm to the top of the cylinder block - I decided that the engine was under the A-76. I ride it, although the car is "not the same" and there is no confidence in the correct conclusion …

At one time, a batch of engines based on 2103 designed for A-76 gasoline (the so-called Chinese version) was made for export. It can be distinguished from others by marking. It starts with the index stamped on the block - 21033 (or 21034) and then the serial number.

In such engines there are “eighth” pistons with oval recesses in the bottoms. When opening the engine on this basis, you can clarify the brand of gasoline required. You should not be guided by the "non-profit" of the pistons to the top of the cylinder block. In addition, this engine is distinguished by an original ignition distributor with modified, specially selected springs of a centrifugal ignition timing controller.

As for the valve seat, it could burn out for reasons not related to a lower (as you expect) compression ratio. This sometimes happens due to manufacturing defects; poor quality fuel may also be to blame.

From the operation department. In a standard VAZ 2103 engine, the piston (nominally!) Really does not reach the top plane of the cylinder block by approximately the amount you specify. And in this case, with a compression ratio of 8.5, the motor cannot work normally on gasoline A-76 (AI-80) due to unacceptable detonation in “load” modes. The output used by the “craftsmen" in this situation - the installation of a later ignition - is not really an output: the engine power is greatly reduced, fuel consumption is increasing, and the temperature regime of the engine is being violated. To normalize the operation of the engine on AI-80 gasoline, it is necessary to reduce the compression ratio, for example, by installing an additional gasket under the cylinder head or by removing the desired volume of metal from the combustion chambers and from the piston bottoms.

I have a VAZ 2105 with a working volume of 1.3 liters. I want to install a cylinder block under a volume of 1.6 liters. Should “native” connecting rods be retained or should they be replaced? What are the pros and cons of installing a Solex carburetor on such a motor?

All engines of the “classic” (from 1.2 to 1.6 l) have 2101 connecting rods. Therefore, when replacing a block from 1.3 to 1.6, there is no need to change them, unless the connecting rods have obvious signs of significant wear ( for example, the piston pin is loose in the upper head of the connecting rod) or they are damaged in such a way that they cannot be repaired (for example, editing after deformation).

Solex carburetors are designed for engines of the "eighth" family. Their feature - work on lean mixtures - requires a more powerful, non-contact ignition system. With the "classic" the use of "Solex" is less effective. Moreover, in some cases this gives a result opposite to the expected one - a decrease in power and even an increase in fuel consumption. As a result, the money spent on buying a carburetor will be thrown to the wind.

Please explain what are the differences between the cylinder heads of the VAZ 2106 and VAZ 2121 3 engines and is it possible to install the 2106 head on the 21213 engine?

The cylinder head 21213 differs from 2106 in two ways: a different shape of the combustion chamber and a higher compression ratio of 9.3; in addition, it has higher strength characteristics (enhanced compared to 2106, since the 21213 engine is more powerful).

The first means that the new head, to put it mildly, is “not aligned” with the old VAZ 2106 unit. In particular, when trying to install it, the 2106 engine receives an excessively high compression ratio and cannot function normally. It would seem that this is not a hindrance - you are interested in the reverse replacement - and with the 2106 head, the 21213 motor could just be a little deformed. But the fact is that the working processes in the 21213 engine are more rigid and for them the head 2106 is not strong enough. Therefore, we consider this option unacceptable.