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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).
The torsional deflection of valve springs in relation to exhaust valve seat erosion in Aero and Phantom engines.

Identifier  ExFiles\Box 66a\2\  scan0023
Date  15th April 1926
  
To R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer}
c. to BJ. RG.{Mr Rowledge} BY.{R.W. Bailey - Chief Engineer}
c. to Hs.{Lord Ernest Hives - Chair}
X.8060

E1/M15.4.26.

RE. EROSION OF EXHAUST VALVE SEATS X.3930
IN AERO AND PHANTOM ENGINES. X.3616 X.8060

Regarding report Hs{Lord Ernest Hives - Chair}3/LGl2.4.26. we find that a helical spring does deflect torsionally when it is compressed, to an appreciable extent.

We made a rough experiment to measure the amount of this movement on valve springs by utilising some apparatus which we have here, and took torsional deflection curves of the E.9. valve springs.

The attached blue print shews the results.

SEE ORIGINAL FOR PRINT AND SKETCH.

The outer springs is wound with a right hand spiral and the free end rotates in a clockwise direction looking from above when the spring is compressed. As would be expected this rotation is in the direction which tends to unwind the coils.

The inner spring is wound with a left hand spiral and is opposed to the outer spring in the direction of its torsional movement.

For the valve lift employed on E.9. the free torsional deflection of the outer spring is 2.5º and of the inner about 3º. No doubt the combined influence of the two springs on the valve is in favour of the outer one.

Rotational movement of the valve may be due to a number of causes -

(1) Torsional deflection of the springs.

(2) Eccentricity of the rocker arm which may synchronise with the valve spring movement.

(3) It is possible that the natural period of swing of the valve torsionally against the springs may coincide with the impulses it receives during the time it is off the seat.

With regard to the question of the seat being ground away it is very clear that oil has been flooding over the exhaust valve on the K.L.M. cyl. that we have here, and the presence of this oil may be the cause of the scale being retained on the valve seat and forming a grinding paste.

contd :-
  
  


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