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).
Analysis of engine valve failures and proposals for further investigation.
| Identifier | ExFiles\Box 179b\3\ img334 | |
| Date | 14th March 1933 | |
| -3- Hs{Lord Ernest Hives - Chair}/Exr.9/BJ.14.3.33. Cont'd.{John DeLooze - Company Secretary} This continued throughout the 30 mins. observations, but the size of the orifice was not increased in the slightest, and the edges only showed signs of fusing. After running for 25 mins. a change was noted on one valve in No.4 cylinder. At a distance of approx. one quarter of an inch from the edge of the seating, a fine line of brighter colour of about three-eighths of an inch long appeared, which had the appearance of the edge of a piece of scale becoming incandescent. This was carefully noted over a period of a further 5 mins. when the test was terminated, and it was found that the valve was cracked in the position noted. This seems to support the possibility of the initial cause of the failure being due to a fracture, a section finally breaking off and is ejected through the exhaust port, and dependent on the size of the orifice, only very slight power loss is occasioned, whereas with actual valve burning the symptoms are usually very pronounced by loss of power due to preignition. The engine was afterwards stripped and the valves removed, and it was found that the two valves which has been run without clearance were practically none the worse, whereas the valve which had cracked was slightly pitted on the seating. It has been noted on all the valve failures which have occurred, that the seatings in the cylinder heads do not suffer to the extent one would suppose, but this appears to be due to the velocity of exhaust gas through the orifice in the damaged valve, causing the valve to rotate fairly fast, with the result that the intensity of the gas is spread over a large area and does not dwell on one spot. Failures have occurred with valve material in D/SLT. and H.R.Crown, both salt-cooled and with both cast iron and Ph/B. valve guides of varying clearances to the valve stems, so we cannot attribute the failures to any particular combination. For confirmation of the possibility of the cause of valve failure, it is proposed that tests are carried out under the conditions under which valves have failed, with the exhaust ports open; when observations of the valves can be made during the various stages until a definite failure occurs. Tests should also be made to prove the heat dissipation of the valve guide metal and clearances, by the use of thermo couples, as from our observations of the colour of the valves a considerable heat flow occurs along the stems to the valve guides, as noted by the almost continuous colour from the head to the extreme part of stem which is visible when operating. Hs{Lord Ernest Hives - Chair}/G.Farmer | ||