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).
Thermostat assembly failure during endurance testing due to the bellows rubbing on the aluminium casting.
| Identifier | ExFiles\Box 156\1\ scan0330 | |
| Date | 25th November 1937 | |
| To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Std. c. HS.{Lord Ernest Hives - Chair} c. Da.{Bernard Day - Chassis Design} c. HPS.{Horace Percy Smith - Experimental Factory Mgr} c. RHC.{R. H. Coverley - Production Engineer} Rm{William Robotham - Chief Engineer}/Std.7/HH.25.11.37. BENTLEY THERMOSTAT SCHEME Lec.3488. We have fitted one of the thermostat assemblies to Lec.3488 and Rm.{William Robotham - Chief Engineer}369 (as being standardised for M series Bentley) on B.9 unit which was running endurance on the test bed. The outlet water temperature ran at approximately 90°C instead of approximately 80°C and the water flow from the top pipe was intermittent (this does not mean that main engine flow was intermittent since the ½" D pass was operating) - the temperature in the normal thermometer position at the rear of the head varying between 87°C and 94°C. Owing to the fact that the endurance running could not be interrupted, it was not possible to determine the cause of this high running temperature at the time. However, after 10 hours running at speeds of 4000 - 4500 RPM, the outlet temperature became very erratic and boiling occurred - the thermostat was therefore removed for examination. It was found that the bellows had been rubbing on the aluminium casting, this was responsible for the high running temperature and had worn a hole in the bellows and let the charge out so that the unit ceased to function. The foul was due to the casting not being to drawing and not being clear of the bottom plate spigot diameter (see attached print of sketch). When the thermostat unit had been assembled the bellows unit had been fitted into case without this foul being noticed - unless suspected it is not visible as it is behind the bellows. When instructing this casing for production will By.{R.W. Bailey - Chief Engineer} please arrange for the spigot machining to be carried right through into the body of the casting so that there is no possibility of this failure recurring. The same thermostatic system is fitted on 3.B.IV car and is running satisfactorily. We have carried out a test with a punctured bellows unit and this results in a low running temperature (approximately 55-60°C with an air temperature of 5°C). Rm{William Robotham - Chief Engineer}/Std. | ||