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).
Analysis of drive 'chunking' issues in various cars and a comparison of V12 and V8 engines.
| Identifier | ExFiles\Box 173\4\ img226 | |
| Date | 5th December 1935 guessed | |
| -2- Chunking in the Drive. So far the only car we have found which does not chunk in the drive is the Buick we tried on the Proving Grounds. All others do, including the Cadillacs, Packards, Lincolns, etc. The Packards and Lincolns were worse than Cadillacs. Lincolns do not regard it as a trouble and seemed unaware of its existence. Packards go to very great pains to reduce slack. We have a drawing of their gear box shewing the very fine limits to which they work with this object in view. But the trouble is evidently still so bad that they are fitting a device to the accelerator pedal to prevent the throttle being closed suddenly. It is a simple oil cashpot which checks the pedal at the last part of the closing stroke. Packards say that Hypoid gears are rather more difficult to control than spiral bevels, but it is difficult to believe this. A possible explanation of the immunity of the Buick from this trouble is that they seem to take particular pains to keep the total transmission slack to a minimum. It is understood that they allow .750 movement at the rim of the rear wheel with the other wheel held firm. This is a maximum, and actually this movement is said to be normally not more than .500. They are also said to have cured a case of chunking on a Buick chassis by reducing the speed with which the accelerator pump supplied petrol to the induction pipe. In spite of the rather contradictory evidence we have so far collected, it looks as though reduction of slack was the most promising line. Hotchkiss is said to be more difficult than Torque tube, because of the extra slacks, and full floating axles more difficult than semi-floating for the same reason. Packards mount their running pinions in the gear box on angular contact ball bearings preloaded so as to be without either radial or end slack. The top and the 2nd. speed jaw clutches have only .002 tangential slack in the jaws. The gear trains .003 and .004 total slack in teeth, this being done by running the 2nd. motion shaft on a stationary shaft which is capable of eccentric adjustments. V 12 and V 8 engines. Now that we have tried both 12 and V 8, there is no doubt the V 12 is smoother than the V 8. The former, however, has a torsion damper, and the latter has not. Also in slow speed pulling the 12 was superior to the 8. This applies to the Cadillac and Packard cars. The big Lincoln was also smooth, but the Zephyr definitely rough. From the evidence given by the damper and flexible flywheel, it seems likely the V 8 can be made very much smoother than | ||