Originally Posted by GTJIM
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!
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thanks Jim!
yes this "groove story" was quite of a debate here also among racers.
in fact all the 23D bearings are 2mm wider than the std CIH ones,
so I reasoned that carving a small groove would probably do no harm to the total load surface.
about the groove requirement in itself I did not know,
so in this case I usually do in such a way the final setup is as close as possible to a known race CIH.
also I guess load/lubrication math done @ 3000rpm with CR25 & heavy cast pistons
can be quite different from 7000rpm with CR10 & light forged pistons?
Hiro