EVOM SPARK PLUG TORQUE CRACKED
Figure 3 shows a spark plug with a deformed housing.įigure 3: Check the housing for uniformity as well as surface damageĪ cracked insulator is often the result of applying too much torque upon spark plug installation. Visual inspection will determine if this has suffered any sort of deformation. The spark-plug housing and thread connects the spark plug and cylinder head. Figure 2 shows the effects of increased clearance on the upper piston ring.įigure 2: Too much clearance results in an unwanted ‘gap’ that impedes energy transfer It also causes increased clearance on the upper piston ring.
The thermal load and shockwaves of pre-ignition and detonation can quickly destroy the electrodes of a spark plug and/or cause a hole in the piston crown. Over torque causes the insulator nose to overheat and start pre-ignition. Some of the consequences of spark plug over-torque can include: The most visible effect will be damage to the plug itself, in particular deformation to the metal housing, which can lead to thread damage and breakage.Ī spark plug damaged by over-torqued installation will not function as intended, and should be replaced immediately to avoid engine damage. If spark plugs are installed over the recommended torque, the plugs will be subject to high stress loads, which can trigger a wide range of issues. What happens when too much torque is applied? This restricts the ability to transfer heat to the shell and cylinder head, causing the insulator nose to overheat and starting pre-ignition. In most cases of under-torque, the vibrations inside the spark plug cause the ground electrode to break down, causing serious damage to the part. If spark plugs are installed below the recommended torque levels, they will not be fully seated in the cylinder head and this will delay the pace of heat dissipation. What happens when not enough torque is applied? Figure 1 shows how heat is transferred for a spark plug fitted with the correct torque.įigure 1: When functioning properly, a spark plug’s heat exchange function results in this heat energy flow
The amount of torque required can vary by manufacturer so it is important that not all spark plugs are fitted in exactly the same way. When manufacturer instructions are closely followed, spark plugs will function correctly, successfully transferring heat out to the shell and cylinder head accordingly. It is essential that technicians consult the manufacturer’s handbook or specification sheet to understand the precise amount of torque required for installation. A secure fastening, where the spark plug is fully seated in the cylinder head, is essential to the spark plug’s capability to transfer heat out of the combustion chamber. Applying the right torque when fitting spark plugs is critical to ensuring a secure fastening DENSO always recommends using a torque wrench to achieve the correct installation torque setting. Installation torque is a measure of force acting on an object, which causes that object to rotate during installation.
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