How to choose a used engine and what should you pay attention to when buying?

Perhaps the most relevant topic that requires a comprehensive analysis is how to choose an engine and what issues need to be taken into account during the purchase process. In the article we will tell you what every buyer needs to know before he is going to buy an engine on the used spare parts market.

Important note

Buying a used engine is a serious undertaking. To minimize all risks, you need to contact only trusted companies with good reviews. Only they provide complete and reliable information about which car the engine was removed from, what mileage it had, what errors there are in operation. In some cases, the buyer can even get a detailed video with the engine running until it is removed from the car. All verified sellers are collected on the portal NSP.AE — here you will find not only high-quality products, but also a list of car disassembly. As soon as we have decided on the seller— we proceed to the inspection.

Appearance

Immediately check if the engine is washed. If yes, then this may be a signal that the seller is hiding various kinds of oil leaks from under the oil seals, gaskets and seals. The fact of the detected leak is not something critical: you just need to check if there are any leaks from under the cylinder head. The remaining weak points are easily repaired already in the process of installing the engine on the car.

The Council. If the engine is washed, then it becomes more difficult to assess its condition. The buyer risks detecting leakage in several places at the first launch, which will result in additional repair costs. If the seller says that the engine has not been washed, but is in a "well-groomed condition", then pay attention to the bends, for example, of the frontal cover. Garbage often accumulates in the places where bends adjoin, which a negligent seller simply cannot wash off — on used engines such a plaque will be visible immediately. This will indicate one thing: the seller wants to hide the true condition of the used engine.

 

We pay special attention to all bolts on the engine. According to their condition, it is immediately possible to determine whether the motor was in a state of overhaul or whether it stood in the car for the entire service life without dismantling. When the bolt is unwound, traces (serifs) from the keys remain on the edges of its head.

However, you should not abandon the purchase if you still found that any manipulations were carried out with the engine bolts - for example, removing the valve cover of the cylinder head may indicate maintenance, re—sealing of gaskets or oil seals.

We inspect the bolts of the valve cover of the cylinder head. Then we pay attention to the fasteners of the frontal cover, and after that we assess the condition of the pallet bolts. A good sign will be the presence of a factory sealant on them.

 

The Council. We need to look at the whole situation as a whole. If traces of keys are found on most of the bolts, it means that the engine was undergoing major repairs. It is better to refuse such a purchase.

Engine oil condition

Unscrew the oil filler cap and carefully inspect it. There should be no carbon deposits, oil clots or dark metallic plaque on the inside. In addition, it is necessary to look into the neck itself to check, if possible, the absence of the same carbon deposits on the internal parts of the engine. The shine and cleanliness of the insides is a good sign for the buyer: it means that the owner operated the engine only with good engine oil.

 

 

By the way, oil is one of the main indicators of engine condition. About how it affects, for example, the operation of automatic transmission — read our article "How to choose a used automatic transmission, what to pay attention to".

We inspect the pulleys and gears

Before buying a used engine, the buyer, of course, receives information about the total mileage of the car. A careful analysis of pulleys (if the engine is equipped with a timing belt) or gears (if equipped with a chain drive) allows you to verify this information.

 

As a rule, both the chain and the belt are parts of long-term operation. The average mileage value is about 100 thousand km for the timing belt and more than 250 thousand km for the chain. This allows you to assess the wear of related parts during the inspection of a used engine.

Serious mileage will inevitably lead to the formation of a so-called "step" on all pulleys — a phenomenon in which the belt "wipes" the metal during operation along the center of the pulley, leaving a distinct trace at the edges, resembling a step.

 

If the belt itself looks good, and the pulleys show a long service life, it is worth checking with the seller why the belt was changed and what led to this. About what questions you need to ask the seller, read our article: "Questions to the seller of auto parts".

A chain drive is almost an "eternal" thing, if we are talking about the proper operation of the engine. As a rule, a gas distribution mechanism of this type serves a good owner for almost the entire life of the car.

 

However, we note that even the reliability of such a part can be called into question if the engine was operated at high speeds all the time. During the inspection, it is worth paying attention to the condition of the gears — there should be no chips or scuffs on their teeth, and the chain itself should not sag between the gears.

Check the candles

The information in this paragraph will be useful only when buying a gasoline engine, because on engines using diesel fuel, the diagnosis of heating candles is reduced only to a visual inspection for the presence of carbon deposits.

Checking the candles is an important stage of the entire engine inspection. Unscrewing is performed using a special "candle wrench" after disconnecting the electrical cables from the contact head. Unscrewing the candle, inspect its insulator. The presence of a yellow-brown plaque may indicate poor-quality fuel on which the engine was operated.

The Council. Only a brown coating speaks of poor-quality fuel. Yellow carbon is often simply associated with a long service life of the candle and darkening as a result of constant exposure to chemically active substances. In any case, the plaque on the candle is an indication of the need to replace it.

 

A small deposit is allowed on the side electrode and the thread of the candle - this will only indicate the need to replace the candles after installing the engine in the car. But a strong carbon deposit should alert the buyer — this may indicate the incorrect operation of the entire injection system. In addition, candles can simply be filled with fuel, as a result of which there will be no need to talk about ideal compression in the future.

We inspect the exhaust tract

If the engine is equipped with an exhaust manifold, it is better to ask the seller to dismantle this part to make sure that the exhaust windows of the engine are clean. Of course, they must be dry. In addition, the presence of oil stains in the windows will indicate increased oil consumption by the engine itself. Light dry soot is allowed.

The Council. If the seller refuses to remove the exhaust manifold, and also forbids you to do it yourself when inspecting the engine, then it is likely that he is trying to hide some shortcomings in this way. The list of malfunctions that the owner may encounter is very wide - from the usual overspending of oil to the failure of one or more valves. It is better to refuse such a purchase.

We pay attention to the crankshaft

During visual inspection, checking the crankshaft involves scrolling it several times with a collar or a special key. In a working engine, the crankshaft scrolls easily, but the recoil from the pistons is felt (which is often called "manual compression"). You need to scroll two or three full turns.

 

If the shaft turns easily, and you feel a kind of "jumps" of the pistons, then everything is fine with the part itself.

 

We use an endoscope

To fully verify the serviceability of the engine, we recommend using an endoscope. This device is a flexible probe with a camera and a flashlight at the end. It is very simple to use it — you need to unscrew the candles (or injectors, if we are talking about a diesel engine), and then insert the end of the endoscope into the resulting hole. Using the camera, it will be possible to see the presence or absence of bulges in the cylinders, as well as to look at their general condition. By the way, there should be no traces of piston movement or oil coating inside.

If you are in a service center…

The procedure for checking a used engine is significantly simplified if the buyer can check the engine at the Service Station before buying. As a rule, two more procedures are carried out in the conditions of an auto repair shop — air leakage in the cylinders is checked and compression is measured.

Checking for leaks in cylinders

To carry out this procedure, it is necessary to completely unscrew the spark plugs from the cylinder head, and then use the leak tightness tester in the cylinder (tester). This device looks like two paired pressure gauges that are connected to an industrial-type compressor. The nozzle of the tester is attached to a rubber tube with a tip, which is screwed into place of the candle starting from the first cylinder. At the same time, by scrolling the crankshaft, the piston of the cylinder being checked is installed in the upper dead center.

For reference. The upper dead center is the position of the piston in the cylinder, in which the bottom of the piston is at the maximum distance from the crankshaft.

Next, the compressor starts pumping air into the cylinder, as a rule, until a pressure of 0.6 MPa (6.1 atmospheres) is reached, which is controlled on the first pressure gauge. The second pressure gauge is equipped with a percentage scale, which shows the pressure loss. On new or relatively new engines, losses should not exceed 5% on each cylinder. On used engines, the loss value can vary within 10%.

Checking compression

The very term "compression" in relation to the engine means the maximum retained pressure that is created by the piston in the cylinder. This procedure is not mandatory when checking a used engine, however, its implementation and recording of the results in the future will assist in the diagnosis of the engine during operation.

To measure compression, you will need a pressure gauge attached to a nozzle with a tip screwed in instead of a candle (starting from the first cylinder). Then, using a pneumatic or electric drill, the crankshaft is unscrewed so that the movement of the piston in the cylinder creates atmospheric pressure, which will be measured by a pressure gauge. As a rule, three or four full revolutions of the crankshaft are enough to create the necessary pressure in the cylinder. The compression values for each engine are individual, therefore, before buying and testing a used engine, it is necessary to familiarize yourself with the technical documentation provided by the manufacturer.

It is important that the compression values on each of the cylinders coincide with each other (or are within the statistical error). This will mean that everything is fine with the cylinder-piston group of the engine.

The Council. Both checks described above imply that there should be no places in the engine through which air will be sucked (except for standard air intake means). Therefore, before carrying out the described procedures, you need to make sure that, for example, the oil filler cap is closed, so that the throttle (if available) is in the closed position, and so on.

Video on how to check a used engine before buying

Together with the Kompart company, we made a video on how to choose the right used engine for auto disassembly.

Summing up the results

Thus, if you correctly check to choose a used engine before buying— you can significantly reduce the risk of purchasing low-quality goods. Recall that you should always contact good specialists and trusted sellers — then any purchase of an automobile part on the used spare parts market will be justified and useful. On the NSP.AE only reliable sellers who provide advice and warranty for spare parts are collected