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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 failure of 40/50 exhaust valves, comparing post-war and pre-war designs and materials.

Identifier  ExFiles\Box 38\4\  Scan047
Date  12th July 1923
  
R.R. 403A (40 H) (SL 12 12-7-23). J.H., D.{John DeLooze - Company Secretary}

EXPERIMENTAL REPORT.

Expl. No. 2764 REF: Hel/LC1S.S.23.

40/50 Exhaust Valves.

There has been a number of failures of 40/50 Exhaust Valves. Samples of the valves received show distinct signs of them having been at an excessive temperature over a portion of the head. The usual form is the seating burnt or distorted and a part of the head badly scaled. We have no record of the pre-war valves failing in service in a similar manner.

The difference between the present standard valves and the pre-war valves is that the present valves are tulip shaped with 30° angle seats - the minimum section between the centre of the head and the seat is .100" - the material is Quickstep steel.

The pre-war valves were flat topped with 45° angle seats and .200" minimum section between the centre of the head and the seat - the material being 3½% nickel.

Comparative tests made with the post-war and pre-war valves under similar conditions show that in order to ensure the valve seating when running under full load conditions it is necessary that the tappet clearance with the post-war valve should be .009", whereas, the pre-war valves will seat with .002". As it is our practice to set the valves with .002" clearance, it means that on cars fitted with the post-war valves under full throttle conditions the valve does not seat.

We have proved that we can reproduce failures with valves if we can arrange the tappet clearance so that the valve does not seat. Our tests show that the worst condition for

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