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).
Cylinder bore finish, its effect on oil consumption, and comparing grinding versus mirror finishing techniques.
| Identifier | ExFiles\Box 103\2\ scan0143 | |
| Date | 10th January 1936 | |
| -2- K/KC/DPB/.10.1.36. All the bores exhibited a hard bearing mark just below the blending of the water jacket into the trunks of the cylinder bores (extensions). This block was returned to W (Hs{Lord Ernest Hives - Chair}/RM{William Robotham - Chief Engineer}) for examination. Another block was fitted and over 100 miles test, no oil was used for all practical purposes. Taking this case in particular, the only factor influencing the oil consumption was the cylinder block itself. From this and in view of my experience in the past I am wondering whether, if the reground blocks that we receive here are a sample of the standard finish, the spasmodic oil consumption on the new cars is not influenced by the same factor. Regarding my own experience here with the old type Bentleys, the cylinder bores of which are ground, I have established over a number of years that if there is a slight whorl due to a slack grinding spindle ( a whorl which is undetectable by a sensitive clock indicator graded in one hundredths of millimetres) bad oil consumption is the inevitable result when using piston rings of a high grade such as those manufactured by Messrs. Brico, and I am wondering whether this slight irregularity has a parallel in the finish of the cylinder bores of the 3½-litres as shewn up in the case demonstrated to GWH.{George W. Hancock - Head Chateauroux} Should you feel that there is something in this question of finish, I am quite willing to let you have a sample for your own personal observation of the cylinder grinding as carried out on the old type Bentleys, so that you can compare the mirror finish obtained on these bores with the finish on the 3½-litre bores, or if you so wish, I will get a 3½-litre cylinder bore ground to the first oversize for you to carry out a comparitive test, in order to satisfy yourself that the test is carried out under the same conditions. I do not wish to enter the field of controversy that exists between grinding and honing schools of thought, but I am of the opinion that a mirror finished cylinder bore cannot but be of assistance in these days where alloy pistons and lapped piston rings are the accepted standard. I enclose a graph reading of the block under discussion - Y.4.BH, shewing you the variations there are between the bores in actual dimensions. K/KC. | ||