Q1 What is the heat rating of a spark plug?
A spark plug must dissipate the heat produced by the combustion gases. The heat rating is a measure of the amount of heat dissipation.
It is essential to use a spark plug with a heat rating that matches a specific engine and its condition of use.
When a wrong heat rating is selected,
When the heat rating is too high,
The spark plug temperature remains too low and causes deposits to build up on the firing end; the deposits provide an electrical leakage path that possibly cause misfire.
When the heat rating is too low,
The spark plug temperature rises too high and induces abnormal combustion (pre-ignition); this leads to melting of the spark plug electrodes that could cause problems such as piston damage.

Q2 How long will a spark plug last?
A Even when a spark plug is correctly used, periodic replacement is required as it is a consumable item.
Examples of problems caused by excessively long periods of use: Worn-out electrodes will have difficulty in sparking.
Deposits accumulated on the firing end may induce abnormal combustion, causing problems that include melting of the electrodes or damaging engine.

These spark plugs require replacement.
It must be noted that these phenomena may also be caused by inadequate engine servicing (fuel systems and ignition system) and incorrect spark plug selection.

Q3 In addition to correct heat rating, what other precautions should be taken during installation of spark plugs?
A Ensure the spark plug has the correct thread reach.
The engine will not operate properly without the proper thread reach.
If a spark plug with the wrong thread length is erroneously used, the piston or valve could strike it and damage the engine. Moreover, there is also the concern that the electrode could overheat and melt.

A Ensure the spark plug has the correct projection dimensions.
There are several types of spark plug igniter shapes.
Sometimes, even when the length of the thread is correct, installing a spark plug with long metal shell projection dimensions may cause it to be struck by the piston or valve and result in engine trouble. Only use projection type plugs as specified by the manufacturer.

When trying to remove a spark plug that is tight and will not come out easily, removing it by force may damage the neck of the threaded section and break the seal section of the spark plug, causing the threaded section to remain in the cylinder head.
To remove such a spark plug without excessive force, first operate the engine and allow it to warm up the cylinder head, then apply penetrating oil to the threaded section.
After a short while, the spark plug can be removed.