Proper operation of the spark plugs is essential to the operation of the engine even though there should be the right type of the spark plugs depending on the type of engine. When the right type is employed, and the engine is well maintained then spark plugs are not normally required in between the scheduled renewal and cleaning should only be attempted with special equipment to avoid damage. In the case of 1.6 litre DOHC engine, engine top cover has to be removed and ignition HT coils and wiring can be removed with the help of special tools or a bend welding rod. The SOHC engines with 1.6 litre capacity have spark plugs installed underneath the upper part of the inlet manifold, which complicates their reach; it is advisable to use special tools to disconnect the HT leads and unscrew the plugs. In the case of the 2.0 litre engines, the engine top cover and securing bolts are removed first and then the ignition HT coils. The spark plug recesses should be cleaned before they are removed to ensure that no dirt gets into the cylinders. Unscrewing the plugs one should make sure to hold the socket in place so as not to break the ceramic insulator. Inspection of the spark plugs can also tell about the state of the engine, and the presence of various deposits are indicative of diverse problems. The gap between the electrode of the spark plug is an important factor in efficiency and they should be altered with care without bending the electrode in the middle. Prior to installation of new plugs, the threaded connector sleeves should be clean and tight to prevent cross-threading, which can be prevented by installing a rubber hose to align them. The plugs must be tightened to the recommended torque after installation and the HT leads and ignition coils must be harnessed up again after reversing the procedure of their removal.