Incorrect installation of spark plugs is one of the most common causes of engine problems, which is often forgotten even by experienced motorists. What is the hard part of getting a candle? However, it is the violation of the installation technology that leads to the burnout of the valves, the destruction of the thread in the cylinder head or, conversely, to overheating and potassium ignition. Puff moment This is not just a figure from the manual, but a critical parameter that ensures the correct heat sink and tightness of the combustion chamber.
Many masters “by eye” determine the effort, relying on experience, but modern engines with aluminum cylinder heads require jewelry precision. Aluminum is softer than steel, and with excessive effort, the thread in the HBC can “float” or crack, which will require expensive repairs with drilling and installing repair bushes. On the other hand, a weak puff will not provide the necessary contact between the candle body and the walls of the well, which will lead to local overheating and eventual failure of the part.
In this article, we will discuss how to correctly calculate the force, what tools to use and why a dynamometer key is not a luxury, but a necessity for saving the life of your motor. We will look at the differences between cone and flat candles, as well as the nuances of installing hot and cold engines.
Why the moment of puffing is more important than it seems
The main function of proper effort in installation is to ensure effective heat sink. The spark plug operates in extreme temperature conditions and excess heat must be transferred through the thread and down washer to the cylinder head. If you do not twist the candle, the contact area will be insufficient, heat will begin to accumulate in the insulator and electrodes, causing premature ignition of the mixture.
Excessive force during tightening carries even more serious risks to engine design. First of all, the candle itself suffers: the metal case can be deformed, and the ceramic insulator can get microcracks, which will lead to breakdowns. But the main danger lies in the damage of the thread in the head of the block, especially if it is made from the head of the block. aluminum-alloy.
⚠️ Attention: Attempting to pull the "leaked" candle on a hot engine is almost guaranteed to lead to a failure of the thread. Aluminum expands more than steel when heated, and the safety margin of the compound disappears.
The tightness of the combustion chamber also directly depends on the force of the pressing of the sealing washer. Insufficient force can lead to a breakthrough of gases, which will result in a loss of power and a characteristic whistling sound from under the hood. In the long term, this is fraught with burn valves and piston group.
Differences of candles: conical and flat washer
The puffing technology depends on the type of seal used in a particular candle model. There are two main types, and they should not be confused, since the physics of the sealing process is fundamentally different.
Candles from flat-puck (flat pressing ring) are the most common in modern cars. Sealing here occurs due to the deformation of the metal ring, which is flattened between the candle body and the plane of the hole in the GBC. It is such candles that require strict observance of the puffing moment, since the ring should be deformed exactly so much as to fill all irregularities, but not to destroy the metal structure.
Cone candles (cone sealed) are less common, mostly on older models or specific engines. They do not have a metal washer, and tightness is ensured by the tight fit of the cone-shaped part of the body to the return cone in the head of the block. Here, the effort is needed to create a tight contact of metals, and the pull here is especially dangerous risk of jamming the candle in the carving.
Always check the type of sealing of a new candle before installing it. If the engine was cone candles, and you put candles with a puck (or vice versa), the tightness will not, or the candle will rest in the piston.
It is important to understand that the length of the thread also plays a role. Long candles (for example, 19 mm or 26 mm) have a large contact area, but the risk of damage to the thread during the stretch is higher due to the lever of exposure. Short candles (12.7 mm) require more careful handling of force.
Table of moments of tightening for different threads
For proper installation, you need to know the diameter of the thread and the type of seal. Below are the averaged data that are suitable for most standard engines. However, it is always a priority to have the technical documentation from your manufacturer on hand. motor-car.
| Diameter of thread | Type of seal | Material of HBC | Moment of puffing (Nm) |
|---|---|---|---|
| 10 mm | Flat puck | Aluminum/Iron | 10 - 12 Nm |
| 12 mm | Flat puck | Aluminum/Iron | 15 - 18 Nm |
| 14 mm | Flat puck | aluminum | 20 - 25 Nm |
| 14 mm | Conical | Aluminum/Iron | 15 - 20 Nm |
| 18 mm | Flat puck | Cast iron | 28 - 32 Nm |
Note that for aluminum block heads, the puff moment values are often at the lower end of the range. This is due to the lower tensile strength of aluminum compared to steel or cast iron. Using values for cast iron blocks on an aluminum head can be fatal.
The golden rule: If you are not sure of the exact moment value for your engine, choose the minimum value from the recommended range for a given thread diameter. Better to slap (and then pull out a little) than to break the thread.
Technology of installation: step by step
The process of installing candles requires not only the right tool, but also compliance with the sequence of actions. A breach of technology can negate even a perfectly exposed moment on the key.
The first thing to do is to clean the candle well from dirt, oil and dust. Using compressed air or a vacuum cleaner before twisting old candles will prevent abrasive particles from entering the cylinder. Dirt in the thread is a guaranteed risk of damage to the turns and incorrect indication of the moment of tightening.
New candles, as a rule, have a factory antifriction coating on the thread. grease Graphite lubricant or oil is strictly prohibited. Oil caught in the gap between the turns, when heated will create excessive pressure (hydraulic wedge), which can lead to a crack in the GBC or a change in the actual pressing force.
☑️ Correct installation of candles
First, the candle is screwed exclusively by hand. This allows you to feel the moment when the thread “caught” the turns. If the candle is tight from the beginning, you need to unscrew it and check for the matching pitch of the carving or the absence of debris. After the candle has sat down by hand, you can use the collar for preliminary fine-tuning, and only at the end - a dynamometer key.
Toolkit: Do I need a dynamometer key?
The question of the need to buy a dynamometer key to replace candles arises often. The answer is unequivocal: for a modern car, especially with an aluminum head unit, this tool is a very useful tool. mandatory. The human hand is not able to calibrate the force in the range of 20-30 Nm with high accuracy, especially in hard-to-reach wells.
There is a method of “anger tightening”, which is often described in manuals for candles with a flat puck, not having at hand a dynamometer key. The essence of the method is to turn the candle after touching the plane by a certain degree (usually 90-110 degrees or 1/2-2/3 revolution). However, this method is extremely inaccurate and depends on the state of the washer and lubrication.
⚠️ Attention: The method of tightening "on the corner" is applicable only to new candles with a new, not yet deformed puck. On old candles or candles with cone seals, this method does not work and leads to errors.
The dynamometer key allows you to exclude the human factor. Even inexpensive models with a rattle give enough accuracy to maintain the car. When working in deep candle wells, it is important to use an extension cord that will not bend, since the curvature of the tool can distort the readings of the device.
Typical errors and their consequences
The most common mistake is to use a too long collar or extension pipe on a regular rattle key. This creates a huge lever, and the effort that seems normal can be many times higher than the permissible norms, leading to the failure of the thread.
The second mistake is to ignore the state of the sealing washer. The puck is a one-off element. When reusing an old candle (or installing a used candle), an old, already deformed washer will not ensure tightness even at the right moment. The heat sink will be broken and the candle will burn.
The “slip” error is also often encountered. If you screw the candle not along the axis of the thread, but with a skew, you can damage the first turns in the head of the block. This is especially true for engines where candle wells are angled or hard to reach. Using a candle head with a magnet or rubber insert inside helps keep the candle even.
What do I do if I ripped the thread?
If the thread is torn, but not critical, sometimes it helps to install a repair candle with an increased diameter of the thread (for example, from 14 to 14.2 mm). However, this is a temporary solution. Full repair requires drilling holes, cutting new carvings of larger diameter and installing a bronze sleeve (throwers).
Do not forget about the purity of the tool. A dirty dynamometer key or a key with backlashes will show incorrect data. Regular verification of the tool is mandatory for professionals, but the amateur should keep the key in a protective case and not use it to unscrew rusty bolts.
FAQ: Frequently Asked Questions
Can I lubricate the candle carving with copper lubricant?
No, modern candles have a special galvanic coating that performs the function of lubrication and anticorrosion protection. The addition of lubricant will change the coefficient of friction, which will lead to the wrong moment of tightening and the risk of "fixing" the candle or, conversely, its spontaneous twisting.
What is the gap between the candle and the piston?
The candle is screwed to the point in the thread, so the concept of "gap to the piston" is not applicable here in the context of installation. The departure of the candle (length of the threaded part) must strictly comply with the engine specification. If you put a long candle in the engine for short candles, it can hit the piston and destroy the engine.
Should I change the candles on the cold engine?
It is recommended to replace candles on a completely cooled engine. On hot aluminum is expanded, and the risk of tearing the thread when twisting or twisting increases many times. You can also get burned.
Why is it difficult to unscrew a candle after a proper tightening?
When the engine is operating in the cylinder, microwelding and oxidation of metals occurs under the influence of high temperatures and pressure. It's a natural process. That is why the next replacement to unwind the moment may be above the moment of twisting, and the use of WD-40 or penetrating lubricant before the procedure will not be superfluous.