The heat number characterizes the degree of heat load of the candle. The lower the glow number of the candle, the higher the degree of its thermal load. At the same time, the candle removes heat better, which eliminates the possibility of glow ignition of the fuel mixture. A candle with a high thermal characteristic has the disadvantage that its self-cleaning temperature is higher. It is more prone to the formation of deposits, in particular when the engine often does not reach its operating temperature during operation, for example city driving, short journeys in winter.
The correct glow rating of the spark plug is determined by the vehicle manufacturer. Spark plugs are available with one or more ground electrodes, with different thread lengths and thread diameters. When replacing a spark plug, use only spark plugs that comply with the vehicle manufacturer's specifications.
Average spark plug life varies. In this case, the material of the electrodes also plays an important role. Chrome-nickel alloy is characterized by very high thermal conductivity and high corrosion resistance. Silver has the best heat sink, and platinum electrodes have high corrosion and burn resistance. The service life of the spark plugs lies between 20,000 and 100,000 km, depending on the material of the electrodes and their number.
Depending on the design of the engines, two types of seals are distinguished between the spark plugs and the cylinder head.
The flat seal has an outer o-ring that is not lost and is fixed to the spark plug body. With a cone seal, no additional sealing elements are required. With limited installation space, in most cases, candles with a flat seating surface and a small spanner size are used. Spark plugs with a conical seat are smaller due to their compact design.
Spark plugs should be changed every 60,000 km.
By the appearance of the candle, we can conclude about the operation of the candles, the adjustment of the carburetor, the state of the mixture and the condition of the engine (pistons, piston rings, etc.) (refer to photographic inserts).
When screwing in the spark plugs, make sure that they are not overtightened, as the sealing washer may be damaged. Do not exceed the tightening torque specified in the Specifications.
Coal deposits
Symptoms: The presence of soot indicates an over-rich air-fuel mixture or a weak spark intensity. Causes misfiring, difficult starting and engine instability.
Recommendations: Check if the air cleaner is clogged, if the fuel level in the float chamber is too high, if the air damper is stuck, and if the contacts are too worn. Try using plugs with a longer insulator, which increases fouling resistance.
The normal state of the candle
Symptoms: Gray-brown color and slight wear of the electrodes. The number of glow plugs corresponds to the type of engine and its general condition.
Recommendations: When replacing spark plugs, use spark plugs of the same type.
Oiling
Symptoms: Lubrication of the candle is caused by wear H•m reflective caps. Oil enters the combustion chamber through worn valve guides or piston rings. Causes misfiring, difficult starting and engine instability.
Recommendations: Carry out mechanical repairs and replace spark plugs.
Ash formation
Symptoms: Soft brownish deposits on one or both spark plug electrodes. The source of their formation are the applied additives to H•m slu and/or fuel. Excessive buildup can insulate the electrodes and cause misfiring and engine instability when accelerating.
Recommendations: If deposits build up quickly, change the Hm deflector caps to prevent Hm oil from entering the combustion chambers. Try changing the fuel gauge.
Overheat
Symptoms: Porous, white insulator, electrode erosion and absence of any deposits. This will shorten the life of the spark plug.
Recommendations: Check if the glow rating of the installed plugs meets the requirements of the Specifications, if the ignition timing is set correctly, if the air-fuel mixture is supplied too lean, if there are vacuum leaks in the intake pipeline and if the valves are stuck. Also check the coolant level and check if the radiator is clogged.
Wear
Symptoms: Rounding of electrodes with a slight accumulation of deposits at the working end. The color is normal. Causes engine start difficulty in cold, wet weather and increased fuel consumption.
Recommendations: Replace spark plugs with new ones of the same type.
Too early ignition
Symptoms: The electrodes are melted. The insulator is white, but may be dirty due to misfiring or foreign particles entering the combustion chambers. May lead to engine failure.
Recommendations: Check the glow number of the installed candles, the ignition timing, the quality of the mixture (isn't it too poor), whether the cooling system is clogged and the lubrication system is functioning properly.
Detonation
Symptoms: Insulators may be chipped or cracked. Insulator damage can also result from inaccurate spark plug gap adjustment. May damage pistons.
Electrically conductive gloss
Symptoms: The insulator has a yellowish color and a polished appearance. It speaks of a sudden increase in temperature in the combustion chambers during sharp acceleration. At the same time, ordinary deposits are melted, acquiring the appearance of a varnish coating. Causes misfiring at high speeds.
Recommendations: Change spark plugs (colder, while maintaining driving style).
Splashing
Symptoms: After misfiring for a long period of time, deposits can loosen while maintaining the operating temperature in the combustion chamber. At high speeds, deposits flake off the piston and adhere to the hot insulator, causing misfiring.
Recommendations: Replace spark plugs or clean and reinstall old ones.
Closing the electrodes
Symptoms: Waste products of combustion fall into the interelectrode space. Solid deposits accumulate, forming a jumper between the electrodes. Leads to ignition failure in the cylinder.
Recommendations: Remove deposits from the interelectrode space.
Mechanical damage
Symptoms: May be caused by foreign material entering the combustion chamber or caused by the piston hitting a spark plug that is too long. Lead to cylinder failure and piston damage.
Recommendations: Remove foreign particles from the engine and/or replace the piston.
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