ENGINE SPEEDS

Hawera Star, Volume L, 7 February 1931, Page 13

ENGINE SPEEDS

INT ERESTING FIG UB ES. It is not many years since a motor engine which ran at 2060 revolutions a minute was considered to he of the high speed type; to-day this speed is considered more in keeping with heavy duty engines, and on many of the modern sports cars speeds of 4000 or •';000 a minute are not at all uncommon. On some of the most efficient supercharged types crankshaft speeds of 70.10 or more a minute must he attained to give the highest road speed the car is capable of. 'this tremendous number of crankshaft revolutions involves all parts of the engine in strains which call for the most perfect methods of manufacture and lor the incorporation of the finest materials. The service called for from the engine involves as a corollary a great deal of care in adjustment and maintenance, and liberal use'of the finest lubricants at all times. When the fly wheel is revolving at these tremendous speeds, other parts , ./"of the engine also are travelling at almost inconceivable speeds. Thus, in \n six-cylinder car witn magneto ignition and running at 4GC)v> revolutions a minute, 12,0 .0 sparks a minute must be produced. If the engine has a j stroke of 4-J-in each piston has to travel j Din for each crankshaft Revolution; that is, it covers 315,000 inches a minute, or 10J0 yards, and the six pistons, therefore, cover GUOO yards, or nearly cl miles a minute. During each revolution each piston stops and starts moving again in the opposite direction 800 J times a minute, and reaches its maximum speed in 1-16,Ub0 parts of a J minute, or l-288th of a second. Tne valves, and especially the exhaust valves, are subject to very heavy strains during this period ot crankshaft activity also. i.aeli valve is snapped open by the revolving cam, remains open for an inconceivably small fraction of a second, then bangs/down on its seat to remain shut for another unction of a second before the cam comes round to deliver it another nibbing blow. The inlet valve has the benefit of the rush of cool gas past it during the period it is. open, but the exhaust valve must withstand the heat of - the burned or even still burning charge being expelled from the cylinder. In a four-cylinder engine it is calculated that each valve is opened more than 126,000,000 times in 10,000 miles. Such bearings as those of the big and small ends of the connecting rods and the main bearings supporting the crankshaft are also subjected to immense strains, and annoying though it may be to have a big end fail in the course of a run, when one considers the strains imposed upon those important components it is realised that it. is really surprising that they stand up to . their exacting work so well. ,