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).
The B.H.B. self-adjusting piston as used on the Bentley during a 24-hour record.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan24 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. -4- Expl. No. REF: Hs{Lord Ernest Hives - Chair}/ACL/L.C10. 10.25. of the B.H.B. self-adjusting piston as used on the Bentley during the 24 hours record. We hope later to have more inform- ation regarding these. It will be seen that this piston differs very little from the former of the two, we tried and described above. I believe the chief point of their patent lies in the inclined stays which attach the head to the gudgeon pin bosses and which they claim expands the skirt under the pressure from the head and makes it fit the bore, but it would appear that this acts in the wrong direction to that desired and would result in unnecessary friction. Its chief characteristic however seems to be flexibility and whatever other factors they claim attributes to its success, I think, are quite minor to the one of flexibility! Appended also is a blue print of a piston which was designed for the Silver Ghost. The general design of this is similar to that of the B.H.B. except that the skirt is not split. It appears that with each side of the skirt split we should have an identical piston to the B.H.B. Looking up records of this piston it seems that in practice it was not very successful and knocked badly! When considering the good results we obtained with the modified standard piston with the split on each side we had in mind a scheme in which the head was separated from the skirt and attached to the gudgeon pin bosses by means of a circular or rectangular XXXXXXXX section member (see sketch). By this arrangement it was thought that it would contd :- | ||