Category: Engine

Hydraulic tappets

The increase in engine temperature is accompanied by a change in dimensions (elongation) hot parts. That is why clearance is necessary, e.g.. between the camshaft and the follower plate. Without the necessary clearance, the valves could become leaky. Valve clearances in older engine designs must be regularly checked and adjusted. In Golf engines, hydraulic lifters take over the task of adjusting the valve lashings, which are maintenance-free. A damaged valve tappet makes itself felt by a rattling noise, which can also occur with operational hydraulic tappets, if:

■ There is still too little oil in the system shortly after the engine has been started. This can happen after the car has been parked for a long time;

■ the car was overloaded at high outside temperatures,

■ If the oil level is too low, the oil pump draws in air.

If the rattle of the valves subsides after an extended ride, but will reappear when driving around town for short distances, it will be necessary to replace the oil drain shut-off valves. To replace a damaged hydraulic tappet (the entire component is replaced) it is necessary to remove the camshaft. This is only for the workshop. On your own, you can check the operation of the hydraulic tappets. This requires a flat feeler gauge and a wooden or plastic wedge.

How a hydraulic pusher works?

The hydraulic lifter is connected to the engine lubrication system. The amount of oil in the lower chamber of the pusher, on which the plunger rests, is variable. In this way, different valve clearance values ​​can be compensated for. With the valve closed, the oil pressure between the two chambers is equalized. The plunger spring pushes it upwards. There is no play between the cam and the valve lever. When the cam hump begins to press against the lever, the plunger is pushed down, whereby a high oil pressure is built up in the lower chamber. Pressure forces and springs push the ball upwards, which closes the flow of oil between both chambers. The piston now rests on the created hydraulic cushion of the lower chamber. The hydraulic valve lash reset acts as a rigid element, on which the valve lever rests. The thrust of the cam can now be transferred to the valve, which opens. After the cam has come off the valve lever, the ball opens the connection of both chambers and the oil pressure can equilibrate.

Compression pressure measurement – Golf 4 , Bora.

Next steps:

1. Warm up the engine before starting measurements. The oil temperature should be at least 30 ° C (the oil filter noticeably warm). With warm oil, the piston rings seal better. However, the engine temperature must not be too high, because when unscrewing the spark plugs you can damage their threaded seats in the head. Remove the engine cover.

Gas engines

2-4 Disconnect the electrical power to the ignition system, remove the ignition coils and remove all spark plugs. Remove the fuel pump fuse and pull out the plugs of the electrical connectors of the injectors.

AHW motors, AKQ, APE/AXP, ATN/OFF: remove the cover over the camshaft cover and disconnect the high-voltage wires and spark plug caps. Remove the candles. Pull the four-pin connector out of the ignition amplification module.

AEH motors, AKL, APF: pull out the four-pin connector (1) from the output stage of the ignition coils (2). Remove fuse no 28 the fuel pump and remove the plugs of the electrical connectors of the injectors. Remove the spark plug caps 1. i 4. cylinder with tool T10029, and candles 2. i 3. cylinder with the V.A.G.. 1922. For APK and AQY engines, all spark plug caps can be removed with the T10029 tool. Remove all spark plugs.

AGN motors, AGU, AQA and ARZ: remove the fuse no 32, thus breaking the power supply to the injectors. Remove the engine cover. Remove the electrical connector plugs from the ignition coils. On vehicles with a turbocharger, it is necessary to remove the ignition coils. On an AGN engine, remove the caps from all spark plugs.

Diesel engines

2 In SDI engines (AGP, AQM) remove the top of the intake manifold. On SDI and TDI engines (AGR, ALH. AHF) remove the connector plug from the fuel shut-off valve on the injection pump and the connector plug from the fuel dose regulator of the injection pump.

3 Remove all glow plugs with a V.A.G key. 3220.

4 Screw the V.A.G adapter into the spark plug socket. 1381/12 and prepare the V.A.G.. 1763 to carry out the measurements.

All engines

5 Apply the emergency brake and put the gearshift lever in neutral.

6 Have your attendant turn on the pacemaker for about five seconds (eight revolutions of the shaft), that is, until the indicator of the pressure tester stops. Reactivating the starter with the accelerator pedal fully depressed will fill the cylinders to the maximum. attention! Do not lean over the engine while the starter is operating, so that the soot particles from the cylinder do not hit you in the face.

7 Read and write down the measurement result. Using a graphical instrument and measurement card, go to checking the next cylinder.

8 The tester must be vented after each measurement.

9 On gasoline engines, re-insert the plugs into the connector sockets on the injectors and the output member of the ignition coils (if it is in your engine) and tighten the spark plugs with a torque wrench.

10 On diesel engines, the glow plugs must be tightened to the torque level 15 Nm. Connect the wires and insert the plug into the socket of the fuel shut-off valve on the injection pump.

The rubber end of the compression pressure tester must be tight against the spark plug socket hole (in a glow plug diesel engine). A helping person, at your signal, he turns on the starter, which must work until the moment, in which the instrument pointer will no longer deflect.

Measure the compression pressure on all cylinders sequentially. More important than the pressure itself are the differences in its values ​​in individual cylinders.

11 On all engines, disconnecting the connector in the injection system will record the fault in the memory of the electronic engine control unit. Such a record can be deleted from the diagnostic memory of the control device at an authorized VW workshop.

If compression pressure is showing symptoms (noise, blowing, sediments etc.) in one of the places mentioned, the reasons for this may be as follows:

■ intake manifold or suction silencer: damaged intake valve,

■ open radiator or coolant expansion tank: damaged head gasket or broken head,

■ open oil filler neck or dipstick: worn cylinder walls, piston skirt (lateral surface) or piston rings,

■ blowing noise in the muffler: leaky outlet valve.

Compression pressure in diesel engines.

Comparing the data in the table of required compression pressure values, we can easily notice, that the compression pressure in diesel engines is in some cases up to three times higher than in gasoline engines. These differences result from differences in the principles of engine operation, or more precisely from different methods of ignition of the charge. In a diesel engine, ignition occurs automatically (hence the other name – compression ignition engine and abbreviation – ZS) due to temperature, which is produced when the air in the cylinder is heavily compressed. In the TDC position of the piston, the temperature in the cylinder of the diesel engine reaches 900 ° C, which is sufficient to ignite the fuel injected into the combustion chamber just before the piston reaches TDC.

This mixture formation method is also different than in a traditional gasoline engine (carburetor, or about indirect injection), in which air and fuel mix outside the cylinder, in the intake manifold. In a diesel engine (but also in gasoline direct injection engines) fuel and air only mix in the combustion chamber. Unlike the previous ZS drive units with indirect injection into the swirl chamber (making their work calmer) modern Volkswagen diesel engines mostly have direct injection, conducive to more efficient operation of drive units and better dynamics of vehicles equipped with them. Further information on direct injection can be found in the chapter on engine controls.

Excessive speed and engine durability.

Operating the engine at excessive speed will shorten its life. Over-rotating engine becomes noisy due to vibration of the crankshaft and moving parts of the valve drive. These vibrations can lead to rupture and fracture of the valve lifters. A faulty mechanism causes the valve and cylinder to be off-cycle and a loss of power. In extreme cases, the valve spring may break and the valve will hit the moving piston, which means very serious engine damage. As a rule, this qualifies the engine for scrap.

Finding faults.

■ When the compression pressure is too low, then pour some engine oil into the spark plug socket hole with an oil can. The oil will seal the space between the walls of the piston and cylinder. Then measure the compression pressure again.

■ If the pressure value is still too low, faulty valves may be the cause, valve guides, head, or a head gasket.

■ If the treatment with oil has brought improvement, this indicates wear of the piston rings, or smoothes the walls of the cylinder.

Compression pressure

In order to establish the technical condition of the engine, the compression pressure in each cylinder should be checked. High pressures are built up in the combustion chamber when the air / fuel mixture is burned, in gasoline engines up to 6 MPa. This means heavy loads on the pistons, piston rings, cylinder walls, valve seats and seals. A leak in the combustion chamber causes increased oil and fuel consumption, deterioration of exhaust gas composition, reduced power and difficult starting of a cold engine. If such symptoms appear, then measuring the compression pressure will help to determine the cause of the fault.

In gasoline engines, the compression pressure values ​​in individual cylinders should not differ by more than 0 0,3 MPa, and in diesel engines, at most o 0,5 MPa.

When in one or more cylinders, the differences are greater, it is a malfunction, which may be caused by the wear of many different components.

Compression pressure guidelines.

The compression pressure values ​​are different for gasoline and diesel engines. Approximate values ​​given in the table refer to engines in good technical condition. It is also worth remembering, that absolute values ​​of compression pressure should not be taken to assess the condition of the engine. It is more important, that the pressure is the same in all cylinders, and any differences did not exceed 0,2 MPa.

Compression pressure required – Volkswagen Golf 4 – Bora

Type of engine	Engine type	Normal pressure – Minimum allowable stress in MPa
Gasoline four cylinders	AHW,AKQ,APE, AXP, ATN, THE END dead, AKL, APF APK, AQY AGN	1,0 – 1,5 1,0 – 1,5 1,0 – 1,3 1,0- 1,3 0,9 -1,4	0,70 0,70 0,75 0,75 0,75
Turbocharged four-cylinder gasoline engine	AGU, AQA, SUPPLY	1,0 – 1,4	0,70
Gasoline five-cylinder	MEMBER	0,9 . 1,2	0,70
Gasoline five-cylinder	AQP	0,9 . 1,4	0,70
Diesel	AGR, AHF, ALH, AQM	2,5 – 3,1	1,90

The compression pressure drops with the age of the engine, therefore the values ​​are smaller, but the same in all cylinders is normal. Only when the pressure value drops below the permissible minimum value, you can start considering replacement, or repair the engine. Pressure differences greater than 0,3 MPa in gasoline engines and 0,5 MPa in diesel engines, indicate one of the following reasons:

– wear on pistons or piston rings,

– Seizure of the rings due to deposition of combustion residues,

– distortion of the cylinders due to seizure of the pistons,

– precipitation from oil and exhaust gas deposits on valve stems and seats,

– curvature of the valves,

– valve burnout (due to too little play).

You can measure the compression pressure yourself, if a suitable measuring instrument is available. For gasoline engines, it can be purchased for little money in a specialized store. Volkswagen recommends a special compression pressure tester V.A.G. 1763 for all engines (an adapter is also required for diesel engines 1381/12). Only the indications of such a meter can be relied on. With other instruments, we can only measure the differences between individual cylinders. You will also need a V.A.G spark plug wrench to perform the measurements. 3122 B and torque wrench V.A.G. 1331 for gasoline engine and articulated V.A.G. 3220 for diesel incandescent lamps.

The help of a second person is essential during the measurements, which will actuate the starter and move the accelerator pedal (You must operate the measuring instrument). In order for the compression pressure measurement to be accurate, make sure, that the hydraulic lifters are working properly, and the starter is serviceable, workshops that rent workstations for DIY enthusiasts have compression pressure gauges, and sometimes also cylinder pressure loss testers, which make it possible to determine the cause of pressure loss.