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 seizure of a vacuum pump cam wheel eccentric, discussing clearances and solutions.
| Identifier | WestWitteringFiles\T\November1928\ Scan048 | |
| Date | 23th November 1928 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/ACL. c. to BJ. Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} DA.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} ORIGINAL Hs{Lord Ernest Hives - Chair}/ACL1/LG23.11.28. 'SS{S. Smith}' VACUUM PUMP - CAM WHEEL ECCENTRIC. X7520 We have had a case of seizure of the vacuum pump conn. rod bearing on the bronze eccentric after the first half hour run on the second SS.{S. Smith} engine. This seizure did not result in damage to the parts, except of course the bush itself which when cool had resulted in wear to the extent of .004 clearance between the eccentric and rod. Looking at the drawings we find the clearances allowed are 1/2 to 1 1/2 thousandth part of an inch. These parts were built up with the minimum clearance of 1/2 thou. Taking the difference between the co-efficients of expansion of bronze and steel as .000008 per deg. C per in., and the maximum difference between the hot and cold temperatures as 80°C, we should expect a reduction of the initial cold clearance of .00156, the eccentric being 2.437" diameter. Working with the minimum clearance of half a thou, would account for the seizure when the engine and oil became hot. We are replacing these parts with new ones having clearance limits of .002" to .003". There is no direct lubrication of this part except by splash from the timing gears. The greater part of the oil splash from the gears is outwards towards the wheelcase due to the angle of the gear helix, but we think sufficient oil will contd :- | ||