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).
Investigation into the cause and remedy for tappet and top valve rocker knocks.
| Identifier | ExFiles\Box 66a\2\ scan0014 | |
| Date | 19th March 1926 | |
| To Hs.{Lord Ernest Hives - Chair} from GWH.{George W. Hancock - Head Chateauroux} As requested I went over to the Test Dept. to investigate the car that EP.{G. Eric Platford - Chief Quality Engineer} had turned down for tappet knocks. I found that the car in question was suffering from two top valve rocker knocks. The trouble with top valve rocker knocks seemed prevalent as I found that they were at the moment working on six cars with this trouble. Their method of curing the knock is to find which side of the valve spring when pressed over, obliterated it, and then by stoning the pad of the rocker arm they produced the necessary side thrust and obtained the quietness of the rocker. The stoning of the pad is a wrong method and it is doubtful whether it will remain quiet for any length of time. To ascertain the cause of the knock and what is the knock, we have carried out exhaustive tests. The results of these we are fairly confident have proved it to be due to the valve seat being out of truth with the valve guide, and the knock is the valve clicking into position when closing also at the same moment the valve stem hitting the valve guide. To obtain this result we carried out the following tests. We started by examining the pads of the rocker arms and observed that the line of contact on the pad was in all cases more towards the heel i.e. rear of the centre line. The design of the pad on the rocker arms, calls for this line of contact to be equal either side of its centre line thus ensuring that none or as little as possible contd :- | ||