Originally Posted by Hiro
remember this is originally a 23D crank:
what I did not know is the 23D lower half-bearings don't have the oiling groove like the std CIH ones,
might not be a problem but this was upsetting me,
so I hand-carved a shallow groove just in case it could improve oiling somehow,
not a gorgeous job I agree...
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Hiro, The diesel bearings have no groove in the bottom half for a very good reason - extra load carrying.
GM did a lot of oil film pressure investigation with the SB Chevy V8 waaaaay back in the late 1950's/early 1960's and found that with the groove in the lower half of the bearing there were two pressure peaks in the oil film and 'zero' carrying capacity over the groove.
Their 'fix' was to use the un-grooved lower half for load carrying capacity and the grooved upper half for oil supply. The lower shell carrys all the load during the firing stroke and the upper half (with the groove) had enough load carrying capacity for the loads imposed by the reversal of the piston at TDC.
The oiling of the lower (un-grooved) shell was completely adequate ... indeed better than with a grooved shell as a better hydro-dynamic 'wedge' of oil was built up under load and the oil film was dragged around by the main bearing journal surface.
So un-grooved lower shells are actually an advantage!