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).
Causes of gumming pistons, ranking various lubricating oils, and considering piston design.
| Identifier | WestWitteringFiles\P\2October1926-December1926\ Scan012 | |
| Date | 11th October 1926 | |
| TO HS.{Lord Ernest Hives - Chair} FROM R.{Sir Henry Royce} C. to BJ. WOR.{Arthur Wormald - General Works Manager} [Struck through] [STAMP: ORIGINAL RECEIVED OCT 13 1926] re. GUMMING PISTONS. [HANDWRITTEN: X3996 X858 (Struck through) X8040 X1588] It is difficult to understand why pistons become gummed if it is not dependent on heat. At the same time it would seem that the lubricating oil would be one of the governing factors. My own impression is that ordinary untreated castor oil would be particularly prone to this fault. I am surprised that you have not a list of the relative merits of the various oils at your disposal. Personally I should expect them to be somewhat in the following order - ( Untreated castor oil........... Worst. All these ( Wakefield's treated castor.... Second. contain veg- ( etable,animal,( Price's compound............ Third. or fish oils. ( ( Wakefield's XL............... Fourth. ( Shell light racing........... Fifth. ( Good quality pure mineral...... Sixth. In all cases the cooler the working piston the less the liability to gum. Also the clearance of the rings may influence the factors. (This refers to the side clearance.) The clearance of the ends of the rings, and the bottom of the grooves, should of course be ample, but I fear at times it may have been insufficient. Regarding the pattern of piston, as far as I know we have given you every type, and the same proportions, as our competitors. Our rings are universally pinned, but I have suggested we test the unpinned rings to see if these are really better or worse. It is an excellent idea to test and find if it follows gas tightness of pistons, which may break down after a certain explosive pressure is reached. The quantity of crankchamber gases, and the temperature, should be taken. R.{Sir Henry Royce} | ||