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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).
Preliminary investigation into the disadvantages of the Aspin engine, covering breathing, installation, weight and reliability.

Identifier  ExFiles\Box 144\4\  scan0087
Date  1st May 1940
  
- 4 -

Cont'd.{John DeLooze - Company Secretary}

DM.{D. Munro}1/M.1.5.40.

The following are disadvantages of the Aspin engine that have so far come to light as a result of a preliminary investigation on the drawing board, by the Aero Division.

DISADVANTAGES OF THE ASPIN ENGINE.

1. Breathing.

The valve area / piston area factor of the Aspin engine, which may be said to represent the specific breathing capacity of a valve gear, if orifice coefficient is neglected, is equal to the poppet valve but inferior to the single sleeve. Since, however, the single sleeve demands wider cylinder centres, and such centres, if used on the other two types, could be utilised to increase the valve area, the comparison gives the sleeve an unfair advantage.

2. Line Engine Installation.

On Vee engines, where to get a reasonable arrangement it is necessary for the intake and exhaust ports to be on opposite sides of the cylinder, the sparking plug position is unpleasantly close to the exhaust port. This disadvantage does not exist on an in-line engine where intake and exhaust can, without difficulty be together on the cylinder side remote from the spark plug.

3. Weight.

As at present designed in cast-iron, the Aspin valve is heavy. It is problematical how much weight can be saved, but it is difficult to believe that fundamentally the Aspin valve need be heavier than the single sleeve.

4. Reliability.

The reliability of the valve under high speed high boost conditions is an unknown factor. Basically, if a 4-stroke engine were designed de novo round the Aspin valve it would appear to be advantageous
  
  


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