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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).
Solutions for 'sparking over' issues on Bentley engines, including plug gaps, terminals, and wiring insulation.

Identifier  ExFiles\Box 63\4\  scan0032
Date  31th May 1933
  
[Handwritten: WST X3109]

To Hs.{Lord Ernest Hives - Chair} from E.{Mr Elliott - Chief Engineer}

[Handwritten: See me HS{Lord Ernest Hives - Chair}]
c. By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Wst. By/RD.

Sparking Over on Bentley.

We have discussed the above question with Hs{Lord Ernest Hives - Chair}/Wst in the light of recent experience on No.3. Bentley.

Some time ago we examined the sparking over distance that was being used on the J.l. early Bensport engines, and we altered the angle of the plug as shown on LeC.3267 to increase the external gap between the plug and the induction pipe to 1/2". This gap obtains with a normal type of 14 m/m plug fitted with spring washer and milled terminal nut.

We cannot use plugs with [Handwritten insertion: cooling] airfins on the central electrode, at the same time we do not think they do any good on the Bensport.

We also cannot do with the K.L.G. spring wire terminal, as Hs{Lord Ernest Hives - Chair}/Wst points out these rotate under the influence of vibration and thereby materially reduce the gap.

It is suggested that we might use an insulated cap terminal connection on the end of the conductor, but there is very little room for threading these through between the induction pipe and the cylinder head.

With regard to the question of the ignition wiring being in contact with the cylinder head, we do not think this matters a bit on the individual leads to the plugs.

We agree that the H.T. wire from the coil to the centre of the H.T. moulding should not be in contact with metal as this conductor is very liable to ozonization leading to the breakdown of the rubber insulation.

Hs{Lord Ernest Hives - Chair}/Wst. tells us that a cambric covering with lacquered finish is a protection against this trouble and it was agreed to try this particular conductor with the protection mentioned, in black finish.

E.{Mr Elliott - Chief Engineer} [Handwritten signature: ORB]
  
  


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