Quote:
Originally Posted by Chrisyphus
We discuss survivorship bias every time we table this conversation in the shop- the evidence points towards that not being the whole story
Stock high-mile motors (150k) coming in with rod bearings about to have a Disco Party, and main bearings showing moderate wear.
Vs.
Low-mile motors with replaced rod bearings, coming in with the front main welded to the crank and the rest of the mains in TERRIBLE condition, while all of the rod bearings look brand new despite their 10-30,000-mile life in the motor. I go into more detail on why this appears to be happening (based on math and theory, until we do more testing) in my first response ITT.
Anyone in this industry knows that "pressure" is often used interchangeably with flow or volume because there's no realistic way to measure flow in the system without installing a dedicated device. This is just rarely ever a distinction that is made because it is unheard of for an engine to run on such a knife-edge of oil flow volume that it matters- any other engine we do has enough oil flow that it hits the bypass pressure and stays there once you're beyond idle.
It is obvious that Peter meant flow here- sharp shooting that is weaponized pedantry and is beneath this discussion, especially from two forum members I respect.
|
Indeed. We don't put "flow" gauges in our cars. We put pressure gauges because pressure is the only readily available proxy for flow.
To be clear about what we are seeing in the flood of S65 rebuilds this year:
Contrast:
(1) High mileage S65s with original stock rod bearings or replaced stock bearings with stock clearances: Rod bearings in near disaster condition, but mains intact
With
(2) S65s with replaced bearings and wider clearances: No. 1 main bearing welded to crank, but rod bearings are fine, save for those that have been affected by the No. 1 main bearing.
We also have yet to see an S65 with a Dailey dry sump fail as a result of a No. 1 main bearing or rod bearing failure.
Yes, this is just our sampling, which one can argue is inherently skewed because engines come to us only when they need to be rebuilt. And there are other explanations, such as expansion of the No. 1 main journal as a result of the torquing of the harmonic balancer bolts, that certainly constitute contributing factors to the phenomenon. But as engine builders, we would be remiss if we did not take into account our experience and that of another builder who sees the same volume of S65s albeit in the race context in concluding that oil pressure (i.e., flow) is an issue in the S65 and that issue appears to be exacerbated, frequently to the level of catastrophic failure, when rod bearings with higher clearances are installed.
Materiality is in my mind the question. BE's analysis concludes the pressure drop is immaterial. We appreciate the analysis, but question many of its underpinnings as Chris somewhat pathologically describes above (I have to work with that crazy genius!), and conclude from our first hand experience that there is an issue here and one that can be rather easily addressed in street motors by installing the SRD gears and in race cars by installing a Dailey dry sump.
Note that as Chris hints, we may develop an alternative internal gear seat for the S65 oil pump that would address the situation more comprehensively.
--Peter