BMW 12121267485 Spark Plug

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The correct functioning of the spark plugs is essential for the engine's proper operation and efficiency. While specific plugs are recommended, it's wise to consult the plug manufacturer's guide when buying new ones, as specifications may change based on experience. Periodically, spark plugs should be removed for examination, cleaning, and potential replacement, especially if they've been used for 12,000 miles (19000 km) or their electrodes are significantly eroded. The plugs' appearance provides insights into the engine's condition: a clean and white insulator indicates a weak mixture or a hot plug, hard black deposits signify a rich mixture, an oily black appearance suggests engine wear, and light tan to greyish brown deposits indicate a proper mixture and a likely healthy engine. If there are long brown stains on the plug's exterior, it implies a faulty joint between the plug body and insulator, necessitating replacement. Sand blasting machines are effective in cleaning plugs and testing their condition under compression; plugs that don't spark at the recommended pressure should be replaced. The spark plug gap, crucial for optimal spark efficiency, should be set to 0.024 in (0.60mm). Use a feeler gauge to measure and adjust the gap by manipulating the outer electrode. Avoid bending the center electrode, as it might crack the insulation leading to plug failure. When reinstalling the plugs, use new washers and ensure the spark plug wires are in the correct firing order: 1, 3, 4, 2, with the first cylinder closest to the radiator. Lastly, regularly clean and wipe the spark plug wires, which typically don't need routine adjustments.

Sparking plugs should be of the recommended type, details of which are given in Technical Data. Inspect and clean the plugs regularly. When removing them, ensure that their recesses are clean and dry so that nothing can fall into the cylinders. Have the plugs cleaned on an abrasive blasting machine and tested under pressure with the electrode gaps correctly set at 0.6 to 0.7mm (0.024 to 0.028in). The electrodes should be filed until they are bright and parallel. The gaps must always be set by bending the outer electrode only. As a general rule, plugs should be cleaned and tested at about 6000 mile intervals and renewed at about 12,000 mile intervals, or before if badly worn. The HT leads from the distributor to sparking plugs and coil should be examined for cracks and defective insulation. Renew any lead found to be defective in any way. Lead connectors are of the plug-in type.