I would suggest that the holes in the impeller are to more balance the pressure on each side of it as without them it would draw itself towards the side with the vanes on it (as it sucks air from that side) causing high axial load on its bearings. A certain amount of recirculation will happen but it may be that that was judged to be the lesser evil.
In my experience the primary cause of failure of these engines (in preservation) is that people let them idle at too low a speed and the master rod to crank bearing fails due to oil starvation as most of the lubrication pressure of this bearing is from centrifugal force within the crank itself and that is negligable below 800rpm. They will idle nicely at 500rpm so people think that that is better - wrong !
David
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24-09-18, 23:15
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