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).
Letter discussing the issue of valves dropping into the cylinder on turbulent head engines.
| Identifier | ExFiles\Box 66a\2\ scan0095 | |
| Date | 21th February 1929 | |
| OY3- Mr. R.W.H. Bailey, Rolls Royce Ltd., Derby, England. Dear Mr. Bailey: Re VALVE GEAR - SECTION 5060 TURBULENT HEAD ENGINE X8060 Y3668 February 21st, 1929. cc - Mr. E.W. Hives, London File We have been quite alarmed to find that on the turbulent head engines the valves can drop into the cylinder if a spring breaks. We do not yet have the tighter-fitting valve guides (.4345 inlet and .4355 exhaust) standardised in England, but are putting these on at the first possible moment. However on "32-CL" (which may or may not have had the tighter guides originally) after running 6000 miles we notice that all the valves will pass into the cylinder with a light push, and that the exhaust valves when pulled out of the guides to the level of the joint face will move .015 either side of center. Since with the head exactly central with the bore the "overlap" of the valves over the bore is only .025 nominal and .0175 minimum, there is very little allowance for wear of the guides. Spring Breakage. On 12-MC our original English Phantom, we have run for considerable distances with broken valve springs without trouble, but we have had a case on one car where a valve has dislodged its top washer and "collets" and has dropped far enough to strike the domed crown of the piston. The blows from the piston bent the valve stem and allowed the valve to drop completely into the cylinder. Evidently if a spring breaks in a certain way the valve can be blown up and down till it throws off the top washer. Under such conditions on turbulent head engines the valve will almost certainly fall into the cylinder. -continued- | ||