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).
Comparison of hairpin type and helical valve springs, specifically the B.60 and a 1937 Norton T.T. spring.
| Identifier | ExFiles\Box 158\5\ scan0029 | |
| Date | 30th March 1939 | |
| 1360 and 10HH TO By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to Da{Bernard Day - Chassis Design}/JNR.{Charles L. Jenner} Rm{William Robotham - Chief Engineer}/JRS.1/JH.30.3.39. COMPARISON OF HAIRPIN TYPE & HELICAL VALVE SPRINGS. A pair of hairpin type springs were obtained and compared with the B.60 valve spring to EB.4373. The hairpin springs were for a Norton T.T. motor cycle of 1937 and for cylinder capacity and valve size should make a fair comparison with the B.60. The loading of the B.60 springs is as follows, Free length 2.1", valve open - length 1.21", load 114 lbs, valve closed - length 1.66", load 47 lbs., while the free length of the Norton spring is 2.06" and the calculated loads are :- at 1.21" 106 lbs, at 1.66" 49 lbs. Thus the difference between the two springs is small and a direct comparison between them can be made. The biggest disadvantage of this type of spring is apparent at first sight. For a multi-cylinder engine it would be exceedingly difficult to find sufficient space for the springs, even for an engine with only one valve per cylinder in the head as in the case of the inlet valves of B.60. The space required by these actual springs is 7 5/16" long by 1 1/4" wide x 1 1/4" high when compressed. This fact is of course of less consequence in a single for which purpose these springs were designed and no doubt the size could be reduced somewhat for a multi. The calculated stress for the hairpin springs is 110,000 lbs/in.2, as against 89,000 lbs/in2. for the helical springs neglecting the effect of spring surge. These figures must notbe taken at their face value as the 110,000 lbs/in.2 for the hairpin springs is a tensile and compressive stress arising from bending while the 89,000 lbs/in.2 for the B.60 springs is shear due to torsion, also it is probable that the stress induced by surging of the spring would be less with the hairpin than with the helical type as the main mass of the hairpin spring has a very small motion and its natural frequencies will be higher. | ||