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Originally Posted by 82ACAUTOCRAFT
I found an article by Jack Merkel relating to the Olds big block and this is what he says about the subject:
"Some people recommend cross drilling #3 and #5 main journals to ensure adequate oil flow to their respective rod bearings. These bearings feed oil to rod bearings number 4, 5 and 8. In all of my experience with Oldsmobile engines I have never seen these particular rod bearings fail. Personally, I think cross drilling has done more harm than good with these engines! Rod bearing failures typically occur with bearings number 7, 6, 1 and 2; rod bearing 7 and 6 are fed oil by main bearing number 4 (cross drilled), number 1 rod bearing is supplied by #1 main bearing (cross drilled) and number 2 rod bearing is supplied by number 2 main bearing (cross drilled). Notice a pattern? David Reher of Reher/Morrison recently reported having experienced rod bearing failures in big block Chevrolet engines with cross drilled crankshafts; replacing those crankshafts with cranks not cross drilled seemed to cure the problem. Here’s the theory: a ½ groove bearing only supplies oil to the rod journal for 180 degrees of rotation, the other 180 degrees residual oil lubricates the rod journal. Cross drilling provides another source for that oil because as one oil hole passes the end of the oil supply groove, the other hole opens up to the groove. But, here’s the problem; in a cross drilled crankshaft, oil has to fight centrifugal force trying to flow to the center of the journal before flowing to the other side where it can feed the rod bearing. If pressure is inadequate to counteract the centrifugal force, oil will actually be forced out of the cross drilled passage and can potentially obstruct oil flow! Oldsmobile big blocks typically have what is referred to as a "fully grooved" main bearing. The oil supply groove runs the full circumference of the bearing. There is really no need to cross drill the crankshaft as the rod bearings have continuous oil flow. Remember, the oil feeding the rod journals from the main bearings do not go through the center of the main journal, these passages are angled toward the rod journal so oil passing through these passages face only a fraction of the centrifugal force that the oil passing through a cross drilled passage would face. Bottom line: in my opinion, don’t cross drill your crankshaft! "
I read in other sites pertaining to the FE that with a cross drilled crank you need to run a lot more oil pressure, otherwise rod bearing failure will occur! |
Overall, I think this is a very technical subject, beyond mine and your understanding, involving many considerations that can have significant impact on function, including oil pressure, viscosity, oil additives, bearing clearence, bearing construction, grooved vs non-grooved, bearing load, angle of oil passage relative to main/rod journal, position of opening on main/rod journal, etc.
I would say that if the experts say you don't need it, then you don't need it.