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).
Proposal for modifying the Phantom III engine with .75' diameter tappets.
| Identifier | ExFiles\Box 96\2\ scan0283 | |
| Date | 13th January 1938 | |
| Rm.{William Robotham - Chief Engineer} BY.{R.W. Bailey - Chief Engineer}/B.1/G.13.1.38. PROPOSED PHANTOM lll. WITH .75" DIA. TAPPETS. With rocker ratio increased from standard 1.333 to 1.45, a valve lift of .35" can be obtained, using a valve spring giving a seat load of 50 lbs, and load at full lift of 106 lbs. There will be a constant excess force available from spring, (referred to valve), during deceleration, of 25 lbs., when R.P.M. = 4500. Maximum scrub distance is taken as .325". There will be a (negligible) increase of duration of 1°-8' (crankshaft angle). Mass of tappet is based on "Wraith" and assumed proportional to diameter. Velocities and displacements at beginning of high acceleration period are identical with standard Phan.lll as given on LeC.5401. Total force in push rod (including that due to 60 lbs/sq.ins. release gas pressure) = 450 lbs., as compared with 430 lbs. for standard Phan.lll. Increased clearance, expressed at valve, due to direct shortening of push rod under 450 lbs. load = .0081" Do. in standard Phantom lll. = .0071" Rankine's crippling load for rod = 650 lbs. Note:- Push rod assumed same length (10.465") as for standard Phan.lll. i.e. to go to top of tappet. Linear pressure intensity at maximum scrub point on cam and tappet contact line = 3000 lbs/1". The above results are obtained by introducing a constant velocity period (of about 21°16'), immediately following the high + acceleration period. --------- Improvements to be sought in design.- (a). Try to make working face of tappet larger than .75" dia. | ||