The Valve Gear


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The slotting head cuts the splines of the inlet rocker which will engage those on the inlet rocker shaft. It is done at an intermediate stage when the blank for the lever still has a large enough flat surface to be supported on parallels over the centre of the rotary table.

At right the blank is formed into an arm on a splined fixture in the rotary table.

                                          ( Quotes are from the maintenance manual. )

“The rocker assembly on each cylinder comprises two sets of concentric rocker shafts. Each set is carried in ball bearings in a rocker bracket and each set operates one inlet and one exhaust valve. The two brackets which lie parallel to each other along the cylinder head are joined together at the end by short bolted-on bridge pieces which form the assembly into a ridged rectangular unit.”   .....................

“Each rocker bracket is in the form of an open sided cylindrical forging with a ball-bearing housing at each end to accommodate the inner rocker shaft bearings. Downwardly projecting lugs provide for the attachment of the unit at the rear to the lugs on the cylinder heads and at the front to the tie rods anchored to the crankcase.”

“As the unit overhangs the cylinder sufficiently to permit the tie rods and the push rods to clear the cylinder fins, the rocker shafts are necessarily comparatively long. The inlet rocker shaft, which is the innermost member of the assembly, extends the length of the rocker bracket and projects at either end to carry on its rear end the rocker arm and on its front end the push rod lever. The shaft is borne in two ball bearings that are housed in the ends of the rocker bracket. The push rod lever is integral with the shaft and forms the anchorage against which the items assembled on the shaft are drawn up. The rocker arm which forms the final item is splined in its boss to engage with the corresponding spines on the end of the shaft.   ...................”

“The exhaust rocker shaft which constitutes the outer member of the assembly lies within the rocker bracket and is formed with a housing at each end for the outer races of the ball bearings upon which it is borne. The inner races are mounted upon the inner rocker shaft, the two races being separated by a tubular aluminium distance piece    .....................”

 The inlet rocker shaft and integral push rod lever were machined from bar. The shaft turned eccentrically to leave enough material for the arm. 

  Here the end is being splined to receive the inlet rocker arm. 

 Mounted on the rotary table the push rod lever is formed and the shaft drilled and tapped to receive the grease nipple

 The radius at the end of the lever is formed using a fixture on the rotary table.

 The shaft and the back of the lever are finished in the lathe.
 The text above is a short example of the beautiful description of the engine in the manual. 

 The perspective section diagrams, such as the one on the left, combined with the text have made it possible to understand and plan the model without the need for a full set of drawings. For some pieces thumb nail sketches have been made but it was usually satisfactory to mark dimensions onto the diagrams.

The exhaust rocker shaft is cylindrical and houses the outer races of the ball bearings which carry it.

The rocker bracket houses the two ball bearings which carry the inlet rocker shaft.