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).
Failures and modifications related to magneto gears and the camshaft drive unit.
| Identifier | ExFiles\Box 143\2\ scan0191 | |
| Date | 24th June 1941 | |
| -6- BY/HB.{C. E. Harcombe}5/EIM.24.6.41. Continued: Magneto Gears. A considerable number of engines are now in Service incorporating both parts of Mod.196 i.e. low pressure oil jet and an oil bath for the steel gear. To date no failures have occurred with this combination which from general aspects is very much better than anything which has previously been experienced. Various other schemes are also being run particularly the use of a hard rubber coupling to isolate the gears from severe vibrational effects. Camshaft and Drive. The most serious feature that has been experienced in this unit has undoubtedly been associated with seizure of the inclined drive bushes and breakup of the thrust pad unit. As the majority of these failures have occurred on Crewe produced engines and in view of the complete reliability of the unit in the past a general check of the parts was carried out and the following features were brought to light. 1. Dimension of the locating bore in the cylinder block for the lower bush being oversize. This would have the effect of allowing the drive to move and become out of line causing loading up of the split bush. 2. Poor finish of the camshaft drive bevels causing irregular motion, heavy loading of the bushes and resultant severe vibration. 3. Want of concentricity between the pitch circle of the inclined bevel and the journal diameter. This would tend to increase the load on the bearing. 4. The possibility of the diametrical clearance between the bearing and the journals being too fine. While all these points were comparatively small a combination of them could produce very serious effects and consequent failure. Steps have also been taken to add a spiral groove to the lower bush to ensure lubrication towards its upper end. Two cases of broken camshafts have also occurred and in each case failure took place through the rear oil hole in No.6 journal following failure of the camshaft retaining stud threads in the cylinder block of the No.7 camshaft pedestal. An examination of the defective parts confirms that failure of the retaining stud threads in the block was the primary factor, this allowing a bending moment to be placed on the camshaft with consequent failure through the rear oil hole - continued - | ||