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 endurance testing, detailing failures, inspections, and subsequent modifications.
| Identifier | ExFiles\Box 86\2\ scan0099 | |
| Date | 25th October 1933 guessed | |
| -2- The pistons ran quite alright for the first half hour (4000 r.p.m.) of the endurance, but towards the end of the second run at 4250 r.p.m. No.6. piston seized, the total full throttle running since start of test being 40 mins. All pistons were removed after No.6. had failed for inspection, and with the exception of No.6. the rest were in very good condition, although one or two appeared to be a little too tight on the bedding surfaces. With the exception of No.1 cylinder all the bores were very scantily lubricated, and in order to improve the lubrication, the skirts of the pistons were given more clearance. No.1 cylinder is always (on Bentley and 20/25 units) more plentifully supplied with oil owing to the fact that a considerable amount of the oil given to the timing gears is thrown into the bore of No.1 cylinder. The extra clearance given to the pistons was accomplished by hand bedding in the following manner:- (1) The clearance on the thrust diameter was increased by .002 over an area extending the full length of the skirt, the width extending to .500 (measured along the circumference) from the near edge of the groove on either side of the pressure side, the opposite side of the piston was treated in a similar manner. (2) From this line .500 from the edge of the groove the piston was gradually reduced a further .001 on each side as far as the near edge of the groove. This is clearly shown on the appended chart of clearances. The pistons were then re-assembled with a new piston fitted to No.6. cylinder. In order to help the cylinder lubrication the main oil pressure was increased from the normal 35 - 40 lbs/sq.in, to 70 - 80 lbs/sq.in. After running 1 hr. No.6. exhaust valve seized in its guide and new valve and guide were fitted, the total full throttle running being 1 hr. 40 mins. At the end of 3 hrs. 40 mins. running a very bad piston knock had developed in No.4 cylinder and on examination No.4. piston showed signs of seizure. | ||