Factory methods of the vintage era
No. 15: Rolls-Royce
Soon after this series was instituted we took a look at the careful and academical methods of construction which made Rolls-Royce cars what they were in 1928. Long before that, circa 1912, F. Henry Royce, yet to be knighted, had evolved his famous, or notorious, bumping-rig, for stressing Rolls-Royce chassis to extremes.
It was said that a well-known American car was chained to this simple but terribly exacting R-R test-bed and lasted for only three minutes. Fourteen other famous cars were reported to have been broken up on it. The story was that although R-R had its own test track at Derby in those pre-1914 days and even went so far as to lay down on it pig-iron bars at six-foot intervals, over which test chassis were then driven, this wasn’t deemed sufficiently punishing and so Royce evolved his bumping rig. The wheels carrying the bump-cams were apparently eight feet in diameter, the chassis for test being kept in place by chaining it to concrete posts in the test house.
After the war the American Springfield branch of Rolls-Royce Ltd. made much of this static but destructive testing, saying that only R-R used such a machine (Dunlop used something similar for testing high-speed tyres to destruction and for assessing steering reaction, in more recent times) and that as a result the R-R technique of using lots of small bolts and nuts at important joints, the use of tubular cross-members, the diagonal braces to the front dumb-irons, the ball-joint mounting for the radiator, the employment of serrations for uniting steering gear and brake corrections, and, indeed three-quarters of the entire car were redesigned from data obtained in this way. It was said that Royce discovered from his bumping-machine that rivets could not be safely used on the chassis frame. Instead, he substituted taper bolts of nickel steel—it was claimed that no car other than a Silver Ghost used such bolts, in 1921.
Other “exclusives” which Springfield claimed for the Rolls-Royce were the integral test pieces of side-members, light alloy crankcase, crankshaft forging, bronze timing gears, gearbox casing, etc. which were laboratory inspected and put on a baby bumping-machine to check the quality of raw materials, heat-treatment, etc. The American publicists also claimed that forged eyes for the front road springs and con-rod forgings machined to remove 3/16 in. of the outer skin, reducing the weight from 8 lb. each in the rough to 2 lb. each when finished, were exclusive to Rolls-Royce. They also made the remarkable statement that Rolls-Royce’s raw materials “cost more than a fine eight-cylinder limousine complete”, whatever that may mean…
By 1923 Springfield Silver Ghosts had close-plating of the nickel parts (again, this was claimed as exclusive to the make), the 32 lb. brake drums were machined from forgings weighing 106 lb., all copper pipe connections were brazed, not soldered, (is this a blinding flash of the obvious?), R-R made all their own nuts, using square-headed, not hexagonal bolts, spring washers were used only for external nuts, otherwise castellated nuts were used, and only four items on the chassis were steel castings, all other steel parts being of rolled steel of forgings, cast-iron being confined to cylinder blocks, piston rings and brake-shoe liners for the side brake—if American publicity can be trusted.
By 1935 more modern machinery, jigs and fixtures were being used in the making of Rolls-Royce and Bentley cars, and the main bearings of the crankshaft were machine bored and reamed rather than hand-scraped, although every surface of the crankshaft, even the webs, were ground to a fine finish.
The gears had their teeth profile ground and the mating shafts were accurately splined and the bearings for them aligned and fitted by mechanical means instead of being stoned by hand and lapped, as in the 1920s. But every gearbox and back axle was individually tested under load. Pistons, including the gudgeon-pin boxes were still diamond turned. It is also interesting to recall that in 1935 Rolls-Royce were still making their own shock-absorbers and all main electrical equipment, and, of course, the radiator.
At Derby they had the benefit of those famous foundries dealing with iron, light alloys and bronze, from which the special R-R light alloys used in the Schneider Trophy aero-engines emanated, and a heat-treatment plant for hardening and tempering alloy steels. The practice of breaking test pieces off components and critically examining them was still in use in the days of 20/25 h.p. and Phantom II production, and the worm and nut steering gear was still run-in on a test-rig. Incidentally, an oil dash-pot was introduced into the controversial R-R gearbox-driven mechanical servo brake system at about this time, purely to obviate a faint click which emanated from it previously when used while reversing.
Each engine was, after assembly, run for four hours on town gas, while filtered oil from an external supply was circulated through it—without danger of petrol pollution of the lubricant. Each gearbox was tested separately, then assembled to its engine. The complete power unit was then run for seven hours on petrol on a Froude dynamometer, during the course of which power and fuel consumption standards were checked. The complete chassis was then given a test lasting some eight hours on a rolling-road dynamometer, power and torque at the back wheels being measured in every gear. The chassis then went out on the road for some 30 miles and, if it satisfied the tester, it was fitted with a sound-accentuating closed test body and each Rolls-Royce or Bentley was driven for at least 50 miles to check that it was running quietly— if not less noisily than its dashboard clock! If it passed this check it was tested again by individual testers and the chassis was ready for its coachwork, after which it was finally road-tested again by Rolls-Royce Ltd.—which caused W. A. Robotham, in his intriguing book “Silver Ghosts and Silver Dawn” (Constable, 1970), to remark that it was a marvel that the vehicle was not completely worn out before it had its body fitted! He is equally scathing about the famous R-R test pieces, remarking that as each piece “weighed several pounds it cost quite a sum to machine”, and no case could be found of a crankshaft being rejected as a result of these tensile tests of sample pieces. Probably Sir Henry Royce would have referred to it as an insurance policy, however…
The 20/25-h.p. and 40/50-h.p. Rolls-Royce and the 3 1/2-litre Bentley chassis were built up each on their own assembly line in 1935, the three lines adjacent. Not far away the engineering apprentices fortunate enough to be at Derby toiled in the middle of a busy machine shop. I wonder if any of them thought to photograph the test chassis as they left the works and roamed the local roads?—W. B.