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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).
Tests and mechanical troubles with 'close-centres' heads, valve lift, and tappets.

Identifier  ExFiles\Box 133\2\  scan0118
Date  1st November 1934 guessed
  
(6)

The "close-centres" head gives the best all round M.E.P. curve with No.4 timing, the overlap of which is almost identical with the normal Bentley timing (No.1).

VALVE LIFT.

Tests have been carried out on the "close-centres" head to ascertain the effect of increasing or decreasing the valve lift, when the unit was running at 4000 RPM. with the 3000 RPM. (18° overlap) timing. It was found that a loss of power was caused by any appreciable alteration in lift, either increasing or decreasing.

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MECHANICAL TROUBLES.

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LEAKING EXHAUST VALVE.

Three more examples have been experienced of leaking exhaust valves - two on the standard Bentley head and one on the "close-centres" - as mentioned in our last two reports.

VALVE TAPPETS.

There has been one case of a broken inlet tappet on the "close-centres" head. It will be remembered that this trouble was experienced on the "Ramp" heads where the angle between tappet and push rods was more acute than on the standard head. The strengthened type of tappets which cured this trouble on the Ramp heads are being adapted to the standard head, so further trouble should not occur.
  
  


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