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).
Test report page detailing experiences with balloon tyres, crankcase bolt shearing, and valve gear clatter.
| Identifier | WestWitteringFiles\Q\2-July1927-September1927\ 110 | |
| Date | 8th July 1927 guessed | |
| contd :- -2- when these were removed and the steering was not so good. In these tests we gave balloon tyres an extended trial. They certainly improve the comfort of the car and give a feeling of increased stability provided they are not run below 35 lbs/sq.in. pressure. We were able to hold the car nearer to the bottom of the banking with these tyres which decreases lap distance slightly. One feature that almost invariably occurs after prolonged high rev. work is that two or three short bolts holding the top and bottom halves of the crankcase together in the centre of the near side, shear - the joint is blown and a bad oil leak is set up. This happened on this occasion and recently on 12-EX more than once. We fitted inner valve springs making a total load valve open of 110 lbs., valve closed 77 lbs. This enabled us to run up to 3100 r.p.m. on 3rd. speed without valve bounce and reduced the valve gear clatter from 2800 r.p.m. upwards. The valve gear is still very obstrusive above 2800 r.p.m. with the cutout closed, however. Summarising the results of the tests :- (1) Balloon tyres. We cannot measure any reduction in speed due to balloon tyres when inflated properly and warmed up. They appear very definitely to absorb a considerable amount of power w until they are warmed up which we believe accounts for our previous result. We can only conclude that their greater windage is compensated for by reduction in wheel spin. contd :- | ||