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).
Piston modifications to improve skirt flexibility and reduce engine knocking.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan23 | |
| Date | 1st October 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. -3- Expl. No. REF HS{Lord Ernest Hives - Chair}/AOL/LG10 10.25. which an attempt was made to make the skirt more flexible by cutting away the stiffening rib, which runs underneath the horizontal split, right round to each drilled boss (see sketch) This piston originally had .003" to .004" clearance but was 'peened' on the split side so that it fitted the bore and was on an average .002 oversize when measured directly over the split across the pressure and non-pressure sides. There was approximately 1/2" strip over which it bedded on the split side. During our first tests with these pistons there was a very slight knock but after about an hour's running under load they seemed to bed down to the bores and were satisfactory. Although it cannot be said that these pistons were entirely free from knocks, it was very difficult to detect any noise without listening with the aid of a sounding rod at the base of the cyl. blocks. With the previous set tested - those split on each side - we could not detect any knocks even by this more exacting test. At this point it would be as well to mention that it is thought to be an advantage to separate the head from the skirt on the pressure side by means of a circumferential split - similar to the one on the non-pressure side - as this reduces distortion of the top part of the skirt caused by the expansion of the head. On the standard pistons we usually find a hard bearing mark at the top of the skirt on the pressure side. Appended is an advert. from this week's 'Motor' of contd :- | ||