From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Guide on engine and bouncing-pin adjustment for knock testing, including procedures, data, and troubleshooting.
| Identifier | ExFiles\Box 27a\4\ Scan077 | |
| Date | 1st November 1931 | |
| 130 REFINER AND NATURAL GASOLINE MANUFACTURER NOVEMBER, 1931 compression gage. The cause of any abnormal change between inspections should be investigated and corrected. Valves. Tappet clearances should be checked, and valves re-ground when not seating. Preventing condensation in engine. When shutting down the engine, it should be run several revolutions with the spark turned off; and, when stopped, the fly wheel should be turned so that the exhaust valve is closed. SUPPLEMENT "A" Engine and Bouncing-Pin Adjustment ADJUSTMENT OF BOUNCING-PIN a.{Mr Adams} The current flowing through the bouncing-pin circuit at a given knock intensity is determined by the voltage applied, the clearance between the gaps, and the adjustment and physical properties of the diaphragm and the various springs. It has not been found possible to manufacture pins of identical characteristics. No definite systematic instructions for adjustment have been found which will always secure the desired result. A description of the procedure may be illuminating. The engine is operated on a fuel of 74 octane number under standard conditions. Sixty readings are taken from the knockmeter at 10 record intervals. The greatest difference between any two of the 60 readings is recorded, together with the average difference of consecutive readings, known as the stability. The stability factor is defined as the product of the greatest difference by the stability. The engine is then checked for quality of knockmeter readings with the same fuel on both sides of the carburetor, and is then operated on a fuel differing from the first one by about 0.5 octane number (74.5). The sensitivity is the difference in average knock-meter readings for the fuels of 74 and 74.5 octane number. The pin factor is then defined as the ratio of the sensitivity to the stability factor. The pins are adjusted until they show a pin factor of about 5.0 under the specified conditions, and are then considered to give good knock-testing operation. Quite satisfactory knock testing may be secured with pins showing a pin factor of much less than 5.0, provided the highest degree of precision (fractions of an octane number) is not required. The following data represent the average of 30 bouncing pins after adjustment: Greatest difference in knockmeter reading, 3.6. Stability, 0.45. Stability factor, 1.70. Sensitivity, 8.4. Pin factor, 4.95. The pin factor may be greatly changed by very small changes in adjustment of the pin. These changes include adjustment of tension of the plunger spring above the contacts, adjustment of the tension of the two leaf springs leading from the contacts, and adjustment of the gap between the contacts. It is not advisable for the inexperienced operator to attempt to adjust the various springs; but if the pin does not give satisfactory performance, the operator should operate the engine alternately on fuels differing by one octane number, and then adjust the bouncing-pin gap, making changes of less than 0.001 in. at a time and measuring the pin factor for each adjustment. A gap of 0.007 to 0.009 in. usually gives the best results, but a difference of 0.001 in. may sometimes make all the difference between satisfactory and unsatisfactory results. DIFFICULTIES Some of the difficulties that may be encountered are listed below, and remedies which may be helpful in each case are suggested in the parallel column: Difficulties Gas evolution too large, acid becoming entrained above the gas in the graduated burette. Gas evolution too small. Bouncing-pin readings have a tendency to drift in one direction. Bouncing-pin readings vary over such a wide range that sensitivity is obscured. Engine missing. Missing cannot be tolerated. An engine that misses only once every hour cannot be used for knock testing. Remedy Suggested. a.{Mr Adams} Reduce degree of knock by lowering compression ratio or by closing throttle. b. Examine bouncing-pin diaphragm, and make sure that it is seated squarely and the retaining nut made fast. a.{Mr Adams} Increase degree of knock by raising compression or opening throttle. b. Examine pin and make sure that it is clean and free to move. a.{Mr Adams} It is possible that equilibrium temperature has not yet been reached. Continue to take readings for 10 minutes. Reduce compression ratio or throttle as necessary until readings become constant. a.{Mr Adams} Make sure that there is no entrained air or gas bubbles or dirt in the carburetion system. b. Make sure that the contact surfaces are clean. c. Examine the diaphragm, and clean the pin with kerosene. d.{John DeLooze - Company Secretary} Examine the pin in the contact adjusting-screw, and make sure that it is not binding at times. a.{Mr Adams} Examine ignition system for: 1, leaks to ground; 2, carbon on spark plug; 3, spark-plug points too far apart; 4, test spark outside of engine to make sure that the coil is in good condition; and, 5, examine breaker system for loose parts. BIBLIOGRAPHY 1Proc., Eleventh Annual Meeting, Amer. Pet. Inst., Sect. III, p. 38. 2Ind. Eng. Chem. 19, 145 (1927). 3Report of Investigations 3152, Bureau of Mines, Nov. 1931. 4J. Soc. Automotive Eng., June, 1931, p. 636 and 637; ibid., July, 1931, p. 45, 52, and 57; ibid., Aug. 1931, p. 129, 134, and 139. 5Natl. Petroleum News, Feb. 19, 1930, p. 24. | ||