How to correctly measure compression in engine cylinders

Engine compression indicates the condition of the engine, its service life, power, and torque. This procedure must be performed every 20-30 thousand kilometers, as well as before purchasing a car. Even when checking at a service center, YOU will need knowledge of “how to correctly measure compression”, because... Servicemen love to deceive and make money from you. Let's start with the theory: Compression is the pressure created in the cylinder at the end of the compression stroke. Another term is appropriate here: Engine compression ratio. The engine compression ratio is expressed in the following ratio: compression/combustion chamber volume.

What compression should be in the cylinders of a VAZ engine?

Normal engine compression is at least 10 bar (1.0 MPa), and the difference between the cylinders should not exceed 1 bar (0.1 MPa). If your compression is 11-12-11-12 from cylinders 1 to 4, then the engine is fine, but do not forget to adjust the valves every 2500 km. If you have 11-9-12-11, then you need to look for the reason and make repairs, because Driving in such conditions will only kill the engine.

How much should the ideal compression be? The ideal compression should be 14 bar for an 8-valve engine in each cylinder with minimal variation (14-14-14-14).

conclusions

It was found that normal compression for a VAZ-2114 engine is 11-14 bar . An increase or decrease in this indicator, as well as a gap of more than 1 bar between the cylinders, is not considered normal and is subject to diagnosis. Engine compression is measured using a compression gauge.

There are several inaccuracies. Firstly, compression is traditionally measured with the engine not running at the starting speed generated by the starter! This is important: the pressure at the end of the compression stroke depends on the crankshaft speed, so if the engine is running, the compression will be much higher than the specified range - up to several times! Secondly, compression is measured on a warm engine (although there are some “former” ones who measure it on a cold engine, but the result is no more than a “funny letter”!). Third, the throttle must be fully open. Otherwise, the required amount of air will not be supplied, so the readings will be underestimated (there is nothing to compress!). On an injection engine, when the throttle valve is fully opened, the fuel supply and sparking stop (so-called cylinder purging). So there is no need to additionally turn off the ignition system (unlike carburetor engines). Fourthly, not only the absolute value of the pressure itself is important, but also how quickly it builds up. This indicator characterizes the condition no less accurately than the pressure itself. Ideally, a fixed value should be achieved in 2-3 “pumps”. And fifthly, the compression level is also affected by the condition of the starter and the flywheel ring gear: if the teeth are worn out and jammed, the compression value will also be underestimated. In general, for a more accurate assessment of the condition, the leak method is now much more often used.

How to measure engine compression?

To check the compression we need a spark plug wrench, a charged battery and a compression gauge. You also can’t do without an assistant.

1. Warm up the engine to operating temperature.
2. We turn out all the candles.
3. We install a device for measuring compression (compressometer) into the spark plug hole that appears.
4. The assistant presses the gas all the way and starts the car within 6-10 seconds.
5. We remember the compression gauge readings and carry out similar operations on the remaining cylinders.

Pressure measurements

We have already answered what the normal compression for a VAZ 2114 should be. Now let's look at how to actually measure it? First we need a special device called a compression meter.

Compressometer

All measurements using it are performed in the following order:

• Fully charge the battery.
• Warm up the engine to 75-90 degrees. WITH.
• After the engine warms up, remove all spark plugs.
• Disconnect the fuel supply hose.
• Insert the measuring device into the first spark plug hole.
• Press the gas pedal and hold it (to do this, two people need to take measurements).
• Start the starter and turn the crankshaft with it.
• Wait until the readings on the dial (monitor) of the device reach the maximum - this will be the compression value in a particular cylinder.
• Move the compression gauge to another spark plug hole and continue measurements.

After the pressure is measured in all cylinders, conclusions can be drawn about the general condition of the engine and the need for its repair/restoration.

If the compression is not normal, then you should stop driving the car and try to solve this problem first. Otherwise (especially if the pressure is very high), the engine may completely fail, after which it will need to be completely restored.

Low and different compression in the engine, what to do?

If, after checking the compression, the compression meter shows below 10 bar in at least one cylinder, then you urgently need to find out the cause and fix the problem, otherwise you risk losing compression in the remaining cylinders.

If, for example, you do not have sufficient compression in 1.4 and any other cylinder:

• We fill a medical syringe with about 10 cubic centimeters of motor oil.
• Spray oil into the hole that appears.
• We measure the compression again.

If, after re-measuring, the compression has increased, it means the rings are worn out. If the result remains the same, it means the valves are burnt out or jammed. Stiff valves can be adjusted, and burnt valves can be replaced.

Debugg

Eliminating the causes of a drop in compression in one of the cylinders directly depends on what was to blame for its occurrence.

Most often, this problem occurs due to the occurrence of rings. The formation of carbon deposits (coking) in one of the cylinders occurs due to the penetration of a large amount of oil into it.

For example, this can happen if the valve stem seals for that cylinder are damaged.

The difficulty of repairing compression loss caused by rings depends on the nature of the damage.

If they just lay there, then you can try to decarbonize them. But if the rings burst, then you will have to disassemble almost the entire engine to replace the damaged elements.

The same applies to valves. If they are misadjusted, it is enough to bring the thermal gaps back to normal. But if the valves and their seats are burnt, then repair work is carried out on the cylinder head - the valves are changed and they are ground in.

Regarding the cylinder head gasket, if it’s all because of it, then they change it. But with the block head, not everything is so simple.

If it was caused by overheating, then you can still fix the problem by trimming the surface.

But if defects form in the body of the head, it is replaced. Any piston malfunction is definitely a replacement.

High compression in the engine. Main reasons.

Don't be too happy if your compression readings are off the charts, this is in no way indicative of how cool your engine is. As stated above, the ideal compression for an 8-valve engine is 14-14-14-14. If your compression is higher than these numbers, then it’s time to think about malfunctions. High compression can damage the partitions of the pistons and tear the cylinders. Below are the main reasons for high/high compression: High compression is created due to excess oil in the cylinder, which is why it is sometimes also called “oil compression”.

• The valve stem seals (VSC) have worn out and died.
• The oil scraper rings are worn out or stuck. (In such cases, oil consumption is inevitable. Check the oil level: How to check the oil level in the engine? Also pay attention to starting the engine after a long stop, for example, in the morning. If the engine oil is consumed, the exhaust will be black).
• There may be carbon deposits in the cylinders. Try to get rid of it by decoking.

Let's sum it up

Taking into account the above, it becomes clear that if the compression in the cylinders has dropped not due to a burnt-out valve or problems with the gasket, then more serious engine repairs cannot be avoided.

Finally, we note that in order to avoid problems with compression on relatively “fresh” engines, it is necessary to pay attention to the quality of fuel and oil, driving style and operating conditions of the vehicle, as well as monitor the condition and performance of the power system. In other words, it is necessary to avoid active carbon formation in the cylinders, since coke and deposits often cause sticking of rings and coking of valves.

Signs of poor compression

If you encounter the problems outlined below, then it is possible, BUT FAR FAR from a fact, that your engine has insufficient compression. Therefore, you don’t need to pay attention to the signs, but you just need to measure the compression.

1. Misfires.
2. Troit.
3. Low dynamics.
4. Engine knock.
5. There is oil.
6. Black smoke.
7. Poor cold start.
8. High fuel consumption (Causes of high fuel consumption on VAZ).

WHAT TO DO IF YOU DO NOT HAVE A COMPRESSOMETER AT HAND?

Is it possible to measure compression without a device? Practice shows that yes, it is possible. But this method will give relative and approximate readings. To measure the compression indicator without instruments, remove the spark plugs from all cylinders except the one being tested. Manually rotate the crankshaft until the compression stroke ends (watch the marks - they should match). Perform this operation on all cylinders one by one. Where the pressure is low, it will take less effort to turn the crankshaft. In this way, of course, you will not get accurate compression readings in the engine. But it is possible to understand the presence of problems.

It is recommended to measure compression every 20-30 thousand kilometers, so every car enthusiast is recommended to have his own compression gauge. Its price is not so high that it is worth saving on it.

The approximate price of a device for measuring engine compression in online stores in the capital is from 600 rubles to 2 thousand. Branded models from Western manufacturers are more expensive – up to 8 thousand. In the regions, a device for measuring compression costs no more than in the capital. Its price varies depending on the manufacturer.

How to increase engine compression in other ways?

There are several options for raising compression without repair. These operations do not in any way guarantee an increase in compression, but you can try. But it is still recommended to eliminate the malfunction by mechanical action - eliminate the malfunction: replace the rings or replace the valves.

• Adjustment of valves. I tried it myself, it really works. The valve could be jammed and therefore not close, resulting in a compression leak.
• Roscoking – removes carbon deposits and excess oil in the cylinder. It only helps with stuck rings; if the valves are burnt out, there is no point in carrying out this operation.

Repair

As can be seen from the above, there are many reasons for different compression in the cylinders. In this case, it is not always possible to carry out repairs yourself, especially if you do not have the skills. In this case, it is recommended to contact specialists at a service station.

Traditional methods of increasing compression

It is noted that the methods described below cannot be a 100% guarantee that compression in the cylinders will increase.

• Buy a quality valve cleaning fluid and pour it into the oil.
• Pour this liquid into the cylinders overnight.

How to properly control pressure in engine compartments

To determine compression, a device is used, which is a pressure gauge with special adapters. Using adapters, this device is connected to the spark plug sockets of gasoline engines or the injector holes of diesel engines. In this case, it is necessary to follow some rules, observing a clear sequence of actions:

• It is important to make sure that the battery is charged and the starter is in good condition;
• Unscrew the candles and thoroughly clean their nests of debris;
• Then carefully connect all parts of the device to the engine through the spark plug holes or diesel injector holes.
• Start the engine, while recording the instrument readings. You should start the engine with the throttle valve open and also closed, comparing the results in the future. Check each cylinder in this way;
• Compare the results obtained with the necessary technical data for a specific vehicle. Based on these data, one can quite accurately draw conclusions about the condition of the timing belt, as well as the piston engine group.

Oil check

Diagnostics can be performed using motor fluid. But for this you will still need a compression gauge:

1. Open the hood and disconnect the high voltage wires from the spark plugs.
2. Unscrew them from their seats. Pour 30-50 grams of motor oil into the sockets where they are installed.
3. Carry out a pressure diagnostic with the device. If the operating parameter has increased, and there is no difference in performance between the cylinders, then repair the seals or rings. They could have coked up. You can replace them yourself. In the case of rings, you will have to remove and disassemble the block head.

Using a compression gauge

To perform the test, you will need an appropriate device. A compression gauge is a simple pressure gauge equipped with extensions, as well as adapters designed to connect to different spark plugs. The types of such devices differ depending on the type of power unit - gasoline or diesel . This is due to the fact that the latter has a higher compression level.

1. Open the hood of the car, disconnect the wires from the spark plugs and unscrew them with a wrench. Remove devices.
2. Prepare the device for diagnostics. Connect an extension cord and adapters of appropriate sizes to it, install them in the spark plug sockets.
3. After installation, sit in the driver's seat and turn the starter device. On a diesel car, when diagnosing compression, it is necessary to remove the injectors.
4. Perform a check on each engine cylinder. The obtained indicators must be compared with those indicated by the vehicle manufacturer. They are usually noted in the service manual.