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

[bearbvd@domain.elided (Greg Hermann)]

>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
>
>
Yes, what you are talking about/doing is appropriate/valid, Russ. No
argument here! It varies from one engine to another, but the geometry of
the oil drillings in the crank is CRITICAL to how oil feeds at high RPM. In
come cases, centrifugal force makes the drillings act like a pump, and
takes all of the oil to the rods. In other cases, the mains get it all. In
some cases the oil simply will not feed inward into the crank from the main
bearings. All of the above can happen in the same engine under different
operating conditions.

I believe that Bruce Crower (quite possibly among many others) had some
interesting , and very expensive, experiences with this design detail on
earlier versions of custom cranks which he made for things like small block
chevies.

Look at all the detail oiling passage and crank drilling changes that Ford
made on their FE series engines in order to get tham reliable for racing
(Nascar and Le Mans). And many stock, 390 cid versions of this engine were
absolutely infamous for throwing their number 7 rod due to inadequate
oiling, and at FAR lower engine speeds than the 427's turned at the end.

I believe that most, if not all, of the Porsche flat sixes feed oil to all
of the rods from a small diameter feeder bearing on the nose of their crank
so as to avoid the centrifugal force problem.

And this whole phenomenon is a VERY good reason for using a stiffer oil
pressure relief spring on an engine which is going to be turning faster
than its original designer anticipated.

Regards, Greg

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