Engine Overhaul — General Information (Opel Astra G)

Engine Overhaul - General Notes

It is not always easy to come to a conclusion about the advisability of a complete engine overhaul, since it is necessary to rely on a number of objective indicators.

High mileage is not a sufficient indicator of the need for major repairs, on the other hand, low mileage does not exclude the need for major repairs. The most important indicator is probably the timeliness of routine engine maintenance. With timely oil and filter changes, as well as with all other necessary maintenance work, the engine serves reliably for many thousands of kilometers. On the contrary, insufficient or untimely maintenance can cause a sharp reduction in engine life.

Increased oil consumption indicates wear of piston rings, valve guides and valve stem seals. It is necessary to make sure that leaks are not the cause of increased oil consumption, and only then draw a conclusion about the unsuitability of piston rings and valve guides. To determine the probable cause of the malfunction, measure the compression in the engine cylinders.

To determine the scope of the upcoming work, check the compression in the engine cylinders. Also conduct tests using a vacuum gauge and determine the nature of the readings of this device.



Check the oil pressure with a pressure gauge screwed in place of the oil pressure sensor and compare the test result with the standard value. If the oil pressure is low, the cause may be wear of the main and connecting rod bearings or oil pump parts.

Loss of power, engine "dips", detonation or metallic knocks, increased noise from the valve timing mechanism, increased fuel consumption indicate the need for a major overhaul, especially if all these signs of abnormal operation appear simultaneously. If performing all the adjustments does not lead to improvement, then the only way to eliminate abnormal engine operation is a major overhaul. A major overhaul consists of restoring engine parts to the condition specified in the technical data for a new engine. During a major overhaul, pistons and piston rings are replaced, cylinders are bored or honed. After repairing the cylinders, which is carried out in a specialized workshop, it will be necessary to install repair pistons. The connecting rod and main bearings of the crankshaft, as well as the covers of the camshaft bearing journals, are also subject to replacement; if necessary, the crankshaft journals should be ground until normal clearances with the connecting rod and main bearings are restored. As a rule, the valves are also subject to repair, since their condition at the time of repair is usually not entirely satisfactory. During a major engine overhaul, repairs are also performed on units such as the starter, generator, and ignition distributor. As a result, the repaired engine should have the qualities of a new unit and withstand significant mileage without failures.

Note. During a major overhaul, important cooling system components such as hoses, drive belts, thermostat, and coolant pump should be replaced. The radiator should be inspected for leaks and cleanliness of internal channels. If you have purchased a reconditioned engine or an incomplete cylinder block, some suppliers do not provide a warranty for the operation of these units without a high-quality radiator flush. During a major engine overhaul, it is also recommended to replace the oil pump.

Before starting a major engine overhaul, read the description of the relevant procedures to get an idea of the upcoming scope of work and the requirements for them. If all the rules and regulations are followed, and all the necessary tools and devices are available, a major overhaul is not difficult to perform, but it will require a significant investment of time. It will take approximately two weeks, especially if you have to go to a specialized workshop to repair and restore parts. Check the availability of spare parts and take care of purchasing the necessary special tools and equipment in advance. Almost all work can be done using a standard set of tools, although precise measuring instruments will be needed to check and determine the suitability of certain parts. Often, the condition of parts is checked in specialized workshops, where they also receive recommendations for replacing or restoring certain parts. Note. You should contact a car service workshop only after completely disassembling the engine and checking the condition of all parts, especially the cylinder block, in order to decide what maintenance and repair operations will be performed in the workshops.



Since the condition of the cylinder block is a determining factor in making a decision on its further repair or on purchasing a new one (or repair) cylinder block, then you should buy spare parts or perform machining operations on related parts only after carefully checking its technical condition. Make it a rule that the true cost of repair is time - then you will not have to pay for the installation of worn or restored parts.

In conclusion, we note that the assembly of any units should be carried out with the utmost care in a clean room in order to avoid further failures of the repaired engine and ensure its reliable operation

Engine diagnostics using a vacuum gauge

Measuring vacuum is a reliable and relatively cheap way to diagnose an engine. The vacuum gauge readings can provide information on the condition of the piston group, the tightness of the cylinder head gaskets, the intake and exhaust manifolds, the correctness of the engine fuel system and exhaust gas outlet adjustments, the exhaust gas throughput, and the condition of the valves (their sticking or burning) and valve springs, and also check the correct adjustment of the ignition timing and the maintenance of valve timing during engine operation.

Unfortunately, vacuum gauge readings are difficult to interpret and the results of reading analysis may be erroneous, therefore, it is advisable to combine vacuum diagnostics with other methods.

The initial factors by which the vacuum gauge readings are analyzed and the most accurate conclusions about the engine condition are made are the absolute reading of the device and the nature of the movement of the instrument pointer (dynamics of readings). The scale of most vacuum gauges is graduated in mm Hg. As the vacuum increases, (and accordingly pressure drop) the instrument reading increases For every 300 m above sea level, the absolute vacuum gauge readings will differ by approximately 25 mm Hg.



Attach the vacuum gauge directly to the suction manifold, but not to other openings through which vacuum is created, separated from the manifold by a channel of a certain length (for example, to the holes in front of the throttle valve).

Before starting the tests, warm up the engine completely. Block the wheels and set the handbrake.

With the gearshift lever in neutral (or in Park position on vehicles with automatic transmission) start the engine and let it idle. Warning: Before starting the engine, carefully check the condition of the fan blades (the presence of damage or cracks on them). When the motor is running, do not put your hands too close to the fan, keep the device at a sufficient distance from the fan and do not stand in line with the rotating impeller.

Check the vacuum gauge reading. On a working engine, the vacuum gauge should show a vacuum of 430-560 mm Hg, and the instrument needle should be practically motionless.

Below is a description of the nature of the vacuum gauge readings and the method for determining the engine condition based on them.

• a. Too low a vacuum level usually indicates a leak in the intake manifold/throttle body gasket, a leak in the vacuum hose, or a too-late ignition timing or incorrect valve timing. Before removing the timing belt covers and checking the alignment of the timing marks, check the ignition timing with a timing light and eliminate all other possible causes using the testing procedures described in this Chapter.
• b. If the vacuum gauge readings are 75-200 mm Hg below normal and are unstable (the arrow twitches), then this indicates a leak in the gasket at the inlet of the intake manifold or a faulty injector.
• c. If the pointer regularly deviates by 50-100 mm Hg, then the reason is the valves are not tight. To confirm this conclusion, check the compression in the engine cylinders.
• g. The needle irregularly deflects toward low readings, or trembles and shows low vacuum. The probable cause is increased resistance to valve movement, or interruptions in the operation of the cylinders. Check the compression in the cylinders and inspect the spark plugs.
• d. If the needle quickly fluctuates within 100 mm Hg at idle speed, and the engine operation is accompanied by smoke from the muffler, then the valve guides are worn out. To check this conclusion, it is necessary to conduct combustion chamber leak tests (with air pumping). If the pointer fluctuates rapidly and at the same time an increase in engine speed is observed, then it is necessary to check the tightness of the intake manifold gasket, the elasticity of the valve springs. Such readings can also be caused by burnt valves and interruptions in the operation of the cylinders (ignition failures).
• e. Weak fluctuations of the arrow (within 20-30 mm Hg in both directions) indicate unstable ignition operation. Check all provided settings and adjustments, if necessary, connect an ignition system analyzer to the engine.
• h. If the needle fluctuates greatly, check the compression in the cylinders or perform leak tests, as the cause of the malfunction may be a non-working cylinder or a leaky cylinder head gasket.
• g. If the instrument readings change slowly over a wide range, then check the cleanliness of the forced crankcase ventilation system pipes, the correct adjustment of the combustible mixture, the tightness of the throttle body gaskets, or the intake manifold.
• i. Open the throttle valve sharply, and when the engine speed reaches 2500 rpm, release the valve. The valve should slowly return to its original position. The vacuum gauge readings should drop to almost zero, then increase and exceed the control readings corresponding to steady-state idle speed by approximately 125 mm Hg, after which the vacuum should be restored to the previous level. If the vacuum is restored slowly, and when the valve is opened sharply, the control reading is not exceeded, then the cause may be wear of the piston rings. If the vacuum is restored extremely slowly, check the cleanliness of the exhaust tract (usually a muffler or catalytic converter). The simplest way to check this is to open the exhaust tract before the suspect section and repeat the test.

Checking the compression in the engine cylinders

• a. The results of the compression test in the engine cylinders allow us to judge the condition of a group of parts in the upper part of the engine (pistons, rings, valves and cylinder head gaskets). Namely, a decrease in compression may be caused by non-tightness of the combustion chambers due to wear of piston rings, damage to valve heads and seats, or burnout of the cylinder head gasket.

Note: To obtain accurate test results, the engine must be warmed up to normal temperature and the battery must be fully charged.

• b. Start by cleaning the areas around the spark plugs using compressed air (if you don't have a compressor, blow out the areas with a car or even a bicycle pump). This is necessary to prevent dirt from getting into the cylinders when measuring compression.
• c. Remove the spark plugs.
• g. Open the throttle valve fully and secure it in this position.
• d. Disconnect the central high-voltage wire from the ignition distributor cap, connect it to ground on the cylinder block. For reliability, connect to ground using a special short-circuiting section of wire with alligator-type clamps on both ends. It also does not hurt to remove the fuse of the electronic fuel injection system on the mounting block, which will ensure complete shutdown of the electric fuel pump when measuring compression.
• d. Insert the compression gauge into the spark plug hole.
• e. Turn on the starter and turn the crankshaft a few revolutions, monitoring the readings of the compression gauge. On a serviceable engine, the pressure should increase quickly. Low pressure after the first stroke of the piston and a slow increase during subsequent compression strokes indicates wear of the piston rings. If the pressure is low after the first stroke of the piston and does not increase during subsequent compression strokes, then the cause is a leak in the valves or a leak in the cylinder head gasket (the cause may also be the formation of cracks in the head). Reduced compression can also be caused by carbon deposits on the valve heads. Record the highest compression reading.
• z. Repeat the measurement procedure for the remaining cylinders, compare the results with the standard data.
• g. Inject some engine oil into each cylinder through the spark plug hole (about three full syringe oilers), then repeat the tests.
• and. If the compression increases after adding oil, then we can make a clear conclusion that the piston rings are worn out. If the compression increases slightly, then the leak occurs through the valves or the cylinder head gasket. Leakage through the valves can be caused by burnt-out valve seats and/or chamfers, as well as deformation of the valve stems or the formation of cracks on them.
• k. If the compression is equally low only in two adjacent cylinders, then the most likely cause is a burnt gasket between these cylinders. Confirmation of this conclusion will be the appearance of traces of coolant in the combustion chambers or in the crankcase of the cylinder block.
• l. If the compression value in one of the cylinders is 20 percent lower than in the other cylinders and the engine runs unsteadily at idle, then the cause may be a young camshaft cam that controls the exhaust valve.
• m. If the compression value exceeds the norm, the combustion chamber is covered with carbon deposits. In this case, the cylinder head must be removed and the carbon removed.
• n. If the compression in all cylinders is low, or varies greatly between cylinders, then it is necessary to conduct combustion chamber leak tests, for which you should contact a specialized workshop. As a result of the tests, leak locations should be accurately determined and a quantitative characteristic of the leak should be given.

Engine Overhaul - Alternatives

When performing a major overhaul on your own, there are various options. The decision to replace the cylinder block, connecting rod and piston group, and crankshaft depends on a number of factors, the most important of which is the condition of the cylinder block. Other considerations include the cost of repairs, access to the equipment of the car service workshop, availability of spare parts, the time planned for the work, and personal experience.

Here are some of the options for carrying out major repairs.

Purchase of individual spare parts

If the inspection shows that the cylinder block and most of the parts are in satisfactory condition and can be used in the future, then the most economically feasible option is to purchase individual spare parts. The cylinder block, connecting rod and piston group and crankshaft should be examined especially carefully. Even if minor wear of the cylinder block is detected, the cylinders are subject to mandatory honing.

Incomplete cylinder block

The incomplete cylinder block contains a cylinder block with a crank mechanism and piston group installed. All mating parts are selected according to size groups, all clearances comply with the standards. The camshaft, valve mechanism, cylinder head and attachments, which are not included in this repair kit, are mounted separately on the block. The costs of mechanical processing are minimal or not required at all.

Engine repair (complete cylinder block)

The overhaul engine supplied as spare parts contains the entire set of the incomplete cylinder block, as well as the oil pump, oil pan, cylinder head, cylinder head cover, camshaft, valve mechanism, camshaft drive gears, toothed belt and belt covers. All parts are installed with new bearings, seals and gaskets. Only the intake and exhaust manifolds and attachments are mounted on the set.



Consider carefully which of the alternatives is best for you. Before purchasing or placing an order for spare parts, consult your local car service workshop, spare parts suppliers, and engine repair specialists.

Engine Auxiliaries - Removal

1. Auxiliary engine components (intake and exhaust manifolds, clutch, spark plugs, distributor and oil filter) can be removed separately from the installed engine, but it is easiest to carry out this procedure during engine overhaul.