SPARK PLUGS AND ENGINE EFFICIENCY

Evening Star, Issue 22247, 27 January 1936, Page 13

SPARK PLUGS AND ENGINE EFFICIENCY

The performance of the engine can be affected considerably by the use of spark plugs which are in poor condition, alt}ip.i)gh not (Positively defective. To obtain the best results, there must be ; no .leakage -of 'the high -tension current, and the gaps should be set to the correct width so that there is a “ ■•fat ” snappy spark which -will ensure quick flame propagation. , 'When the -points of the electrodes -become burnt and pitted, or the insulating core is encrusted with carbon deposits, there is bound to he some loss of efficiency. The fault might not be pronounced; merely a general fallingoff in the liveliness of the engine and its acceleration with, perhaps, some increase in petrol consumption. The spark plugs should be removed and examined after every few thousand miles’ running, the cores cleaned, and gaps checked with a feeler gauge and reset if necessary. If the plug is so constructed that the core can be removed, it should be dismantled and the core cleaned with petrol. Care should be taken never to scrape the porcelain insulation with any sharp instrument which might scratch the glazed surface. In the case of plugs which cannot be taken to pieces, an easy method of cleaning is to steep the plug in petrol or methylated spirit, and then remove the carbon from the insulation with a strong bristle brush or sharp splinter of hardwood.

When replacing a detachable core the gland nut and the thread on the shell should be clean and free from grit, and the copper sealing washer should not be forgotten. The nut should be screwed home firmly, but not with excessive force. A feeler gauge is essential for the right setting of the gap, and in most cases the correct procedure is to bend the outer electrode only with a fine pair of pliers until the desired gap is obtained. If the central electrode is treated in this way there is always a risk that the porcelain might be cracked, and with multipoint plugs it would be impossible to adjust the gaps accurately by moving the central electrode. Beore a plug is put back in the engine the metal round the aperature in the cylinder block and the copper asbestos washer must be wiped clean. As soon as it is felt that the flange of the plug is biting on the washer, the spanner should be used slowly and carefully. A moderate pressure should ensure a complete seal, but if the washer is worn and it is suspcted that there might be some loss of compression, oil should be squirted round the base of the plug while the engine is running. If bubbles then appear in the oil it will be obvious that there is a leakage.