Quote:
Originally Posted by serranot
There is only one path--mains -> rods. If oil flow through the rods is increased, then it's coming from the mains. Can't have one without the other.
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I disagree that it is that simple. Here is my take on this (electrical engineer waxing about mechanical stuff - yikes):
The oil enters the main bearings from the main oil gallery. From there, it has 2 paths of flow.
The first is across the main bearing surface. This is the actual oil that squishes out the sides of the main bearings and forms the oil wedge that lubricates the main journals and keeps the crank happy as a clam.
The second is through the oil galleries drilled through the crank to the rod journals. Once the oil gets to the rod journal, it squishes out the sides providing the rod bearing oil wedge (if clearances allow for adequate squishyness).
The S65 rod galleries are in the middle of the main journal, just like most other engines. The rod gallery lines up with the groove in the center of the main bearing shell. So while the increased flow will pass "through" the main bearing, the oil flow across the main bearing surface should remain unaffected if available oil pressure remains the same.
In this regard, SneakyPete is correct. Technically, one would expect the flow across the main bearing surface will be reduced slightly. This is due to the 3%-4% drop in available oil pressure after changing to BE rod bearings. The drop in pressure is due to increased flow losses upstream of the crank (more flow in same pipe causes greater flow losses).
I hope that the main bearings are not so sensitive that the small drop in flow will cause them an issue. The variance in oil pump from car to car might be higher than 4% from factory. I will glady accept this slight reduction in main flow in order to increase the rod bearing flow.
And here is a nice PDF from
Mahle that shows the bearing failure modes.
I am by no means an expert on engines. If I am wrong, please let me know.
Cheers,