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).
Inaccuracy of the F.XI & XLI timing device and proposing an alternative 'oil tube method' for valve timing.
Identifier | ExFiles\Box 33\4\ Scan103 | |
Date | 10th December 1927 | |
To RG.{Mr Rowledge} from Hs{Lord Ernest Hives - Chair}/VH. c. to BY.{R.W. Bailey - Chief Engineer} X1770 Hs{Lord Ernest Hives - Chair}/VHl/LG10.12.27. RR. F.XI & XLI TIMING DEVICE. DES.693. We have used the above timing device for finding top dead centre and setting the magneto to timing. The inlet opening position as marked on the scale represents I.O. at 20º B.T.D.C. This is not correct. With standard working clearances (.020") I.O. is approximately 2º A.T.D.C., with .010" clearance I.O. averages 6º B.T.D.C., and with .030" clearance I.O. averages 8º A.T.D.C. All of these positions are so near to T.D.C. when taken on a stroke basis, as to absolutely condemn the use of this timing device for accurate valve timing. After finding T.D.C. with the timing device, we have checked the position by setting a pointer to zero on a degree plate, and finding T.D.C. again by the 'oil tube method'. This method involves removing the inlet plug and filling the combustion space with a thin oil when the piston is nearly at the top of its stroke (felt with a finger). A short piece of glass tubing fitted to an old plug body, then replaces the inlet plug and when the piston is moved over T.D.C. a column of oil moves rapidly up and down the glass tube. T.D.C. is indicated by the highest position of the oil, and the extreme accuracy of this method will be realised when it is seen that the multiplication of the pistom movement as observed in the oil tube is in the same ratio as the square of the diameter of the piston over the square of the oil tube dia. (internal). contd :- | ||