My interest in this thread comes from trying to solve an oil leak at the O-ring barrel to head joint. The diameter of the oilway through the O-ring spigot is 3mm - a c.s.a of 0.7mm².
That is exceeded by the 4 oilways through the lobes which, should they sum to the same area, would be only 0.75mm in diameter.
As the pump is a constant volume type, the pressure in the cam can be increased by restricting the flow out of the cam end. This is the pressure experienced by the O-ring.
I wanted to observe the oil flow to see what is going where with the engine running so made up a viewing window to replace the bevel cover. I assumed most oil entered the chimney via the external oil lines. What did occur was the bevel chest soon filled with oil via the two holes between it and the cam chamber. It was the same with or without the cam end fitted with a blank although faster to fill without the blank. Either way, the cam is running in an oil bath as is the bevel.
Without the blank, there was no leak at the oil seal. Mr Lacey uses a restriction (as posted early on this thread) of "around 2mm". I will give that a try.
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