[Healeys] Oil Pumps

Bob Spidell bspidell at comcast.net
Wed Jan 1 14:24:46 MST 2020

Cavitation at the pump resulting in aeration of the oil?

On 1/1/2020 12:16 PM, Michael MacLean wrote:
> Well, then explain to me why a Bugeye I had back in the 70s would read 
> 60 PSI at speed when the proper amount of oil was in the engine.  At 
> one quart low, it would read 40 PSI at speed.  Put in a quart and the 
> pressure would go right back up to 60 PSI.  It amounted to a rolling 
> oil change with intermittent filter changes.
> Mike MacLean
> On Wednesday, January 1, 2020, 11:24:06 AM PST, WILLIAM B LAWRENCE 
> <ynotink at msn.com> wrote:
> Oil pumps, vane, rotary and gear type are all positive displacement 
> devices, meaning that they will continue to build pressure against 
> resistance to the point where something breaks. That is why they are 
> all equipped with a bypass valve which limits the amount of pressure 
> in the system. The amount of stress on the geardtrain is directly 
> proportional to the pressure developed. I'm not sure if the problems 
> related to the rotary type pumps is a result of the stress of driving 
> the pump or to the larger pressure pulses (vibration) that are 
> inherent in the design.
> The manufacturer selects the bypass valve and spring assembly that 
> will keep the pressure within a safe range while protecting the drive 
> system from over stress. The four cylinder engines are supposed to run 
> at a maximum of 50-55 PSI, the sixes somewhat lower, and it is the 
> bypass valve that maintains that pressure even though the pump itself 
> is capable of much higher pressures if it encounters excessive 
> resistance.
> Viscosity change in the oil when at higher temperatures will reduce 
> pressure by reducing the resistance of the oil circulating through the 
> various clearances in the engine. As the engine wears these clearances 
> will increase thus reducing resistance and dropping oil pressure. Oil 
> pressure alone is not as important as is a constant flow of oil to all 
> components combined with the film strength of a good quality oil.
> Bill Lawrence
> BN1 #554
> ------------------------------------------------------------------------
> *From:* Healeys <healeys-bounces at autox.team.net> on behalf of Kees 
> Oudesluijs <coudesluijs at chello.nl>
> *Sent:* Wednesday, January 1, 2020 6:37 PM
> *To:* healeys at autox.team.net <healeys at autox.team.net>
> *Subject:* Re: [Healeys] Oil Pumps
> Absolutely correct. There may be theoretically a tiny difference,
> immeasurable probably, caused by the efficiency of the various pumps.
> Kees Oudesluijs
> Op 1-1-2020 om 19:24 schreef Bob Spidell:
> >
> > I'm not a fluid dynamicist, but wouldn't, say, 45psi from either a
> > vane/rotor type pump put the same load on the cam gear and driveshaft
> > as 45psi from a gear-type pump, all other factors--oil viscosity,
> > etc.--being equal?  Or, is there some other factor(s) at play?  Do the
> > gear-type pumps produce lower pressure (seems to me that's the only
> > way they'd reduce the load on the gears and the cam thrust plate)?
> >
> > Bob

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