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Ta .. that clarifies things.
Clearly the reduced central portion is maximised along the length, perhaps suggesting that the aim was to maximise the volume of the oil-holding void and hence ensure a more reliable supply of oil to the needle bearing.
This further leads me to suspect that the hole in the shaft is merely an air bleed, its only purpose being to "allow" the oil to flow rather than to "cause" it to flow.
I say this because there is no point in exhausting the flow from the hollow shaft .. indeed the aim would probably be to retain as much oil in there as possible.
All somewhat conjecture though.
The rough finish on the central part of the pushrod will be there, as I'm sure you realise, because its the finish left from the turning operation, after which only the end seal and bearing surfaces would have been ground.
It may contribute to oil movement but if it does I would say that its probably a happy accident rather than an intended design ploy.
The only outstanding element in all this of which I am still a tad uncertain is the detail of the case/bearing/seal arrangement behind the clutch where the bleed hole in the shaft is.
If anyone has a pic of this I would be interested to confirm my reasoning that the bleed hole must exit between seal and bearing, thereby allowing the oil to flow back through the bearing and thence into the inner crankcase.
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