Re: alfa-digest V7 #630 - Restrictors in the oil passages

[AlfaNeely@domain.elided]

Simon,
	I was not suggesting that everyone partly plug off the oil passages 
to the cam bearings and I am not sure I agree with it.   However, my friend 
HAS done this to 5 of the 6 bearings and his engine is alive and well in a 
racing environment.  Thus, all the concern about roll pins constricting oil 
flow to the cam bearings was, I felt, of no consequence.  That was the point 
I was trying to make: roll pins are not going to limit oil flow enough to 
matter.
	I too read the article in Sports Car.  Maybe I will go read it again. 
 It was pretty interesting.  Especially the way oil pressure and flow 
interact with the "leakage" around the bearing surfaces.
	Your comment about oil pressure at the rod bearing due to centrifugal 
force is appropriate to the Alfa four cylinder.  Study the crank and it is 
obvious that oil to the #2 and #4 main has to travel out to the rod journal 
and BACK against the centrifugal force.  That is the reason I drill the block 
for full oiling to all five main bearings.
    Finding fully grooved inserts for all five main bearings can be a 
problem.  It is necessary to drill a hole in the 2 & 4 bearing inserts.  Some 
parts purveyors do not understand what I am asking them to look for in their 
bearing package.  Given the recent thread, I sure ain't gonna ask that by E 
Mail!
Ciao,
Russ Neely
Oklahoma City


In a message dated 4/10/99 2:09:54 PM Central Daylight Time, 
owner-alfa-digest@domain.elided writes:

<< Date: Fri, 09 Apr 1999 14:44:56 -0700
 From: Simon Favre <simon@domain.elided>
 Subject: Re: Restrictors in the oil passages
 
 This one is also new to me. I don't think highly of it. There was a VERY
 good analysis of engine lubrication in a recent issue of Sports Car (the
 SCCA national rag, not the Euro auto rag). In this article, a racer with
 a considerable background in Mechanical Engineering analyzed why he kept
 getting a specific bearing failure running a motor at 8000+ RPM. The 
 culprit in his case turned out to be a very curious consequence of the
 physics. It turns out that the centrifugal force acting on the oil in
 the crank passages caused the oil pressure at the rod bearings to go up
 and the oil pressure at the mains to go down! He was having failure on
 one main bearing quite consistently. His conclusion was that it was oil
 starvation at this main caused by having to feed the nearby rod bearings
 which started sucking oil out of the main faster at high RPM. His system
 was a typical racing dry sump with a pressure limit valve. 
 
 The author then went on to analyze lubrication systems in great detail.
 I'll have to dig it up to summarize more. I think one of his conclusions
 was that fitting a high volume oil pump didn't help if you were running
 at the max pressure allowed by the standard limit valve (assuming WOT).
 In his case, he had to raise the pressure in the system to accomodate
 the pressure loss at the mains running at redline. There was no mention
 of restricting oil flow to the head. I think he did more work on the
 block to balance the flow to the mains.
  >>

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