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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).
Faulty A.T. Speedometer reading, which varies with temperature.

Identifier  ExFiles\Box 70\3\  scan0380
Date  2nd March 1928
  
BY.{R.W. Bailey - Chief Engineer}
c. Hs.{Lord Ernest Hives - Chair}
c. CWB.
c. JLE.{J. Lee Evans - Chassis Test Manager}

X8783-p

EP{G. Eric Platford - Chief Quality Engineer}5/H.{Arthur M. Hanbury - Head Complaints} 2.3.28.

re. A.T. SPEEDOMETER. FAULTY READING. X4308

In checking the Speedometer on the road during our final run of the chassis 29-FH, it was considered that the Speedometer fitted, i.e. No. A.359/730 was reading slow in M.P.H. On returning it was immediately tested on our test bench rig and found to be actually reading 7% slow, although on the previous test bench rig it showed the speedometer to be correct.

The speedometer was allowed to rest overnight, and was again tested this morning on the rig, the temperature of the instrument being much lower, and found to read correctly.

The variation in the speedometer reading by the temperature has recently been reported on by Hs{Lord Ernest Hives - Chair}, but it would appear to be a feature which is not very clearly understood, and may easily account for the variations which are reported on from time to time as regards comparative tests.

It appears to me that in order to be on the safe side, instructions should be given to the makers for the speedometer to be set O.K. under normal temperature conditions which the speedometer will go up to when running on the car, as otherwise our speedometers will always be reading low when in the hands of the customer, which is not to our advantage.

I take it that under the present circumstances there is no alternative but to pass these speedometers in this condition, but we shall be glad if you will take the point up with the makers.

EP.{G. Eric Platford - Chief Quality Engineer}
  
  


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