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Thanks Terry - that's quite a bit of pressure then!
Do you have to machine the ball seat to suit the plunger?
Does anyone happen to know at what pressure the standard A7 ball valve cracks open?
I'd imagine most splash fed 7's don't generate enough back-pressure to open it, unless perhaps using SAE50 on a winter's morning.
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Location: Ilkley
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Chris , with an oversized A7 pump over 100 psi when cold is too easily obtainable.
I set my PRV when hot at 60 psi / 5000 rpm , approx 25 psi / idle
More than adequate for sprints/hill climbs !
Geoff
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Yes but is that a splash fed engine Geoff? And if you don't mind me asking what oil grade are you using?
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Chris the standard oil pump circulates more oil than can pass through the jets so the PRV is working constantly especially when cold. Bench flow tests with an open oil pan using SAE30 show quite a lot of oil returning to the sump at over 8/10lbs. The Paul Bonewell high pressure valve does not need any mods if the ball seat is OK. Terry.
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Chris , pressure fed crank .
Have had no problems with Halfords Classic 20/50 .
Geoff
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OK, understood: Thanks Geoff and Terry.
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So,Is it necessary to fit a larger pump than the 7 one if you cure the engines inherent "leaks ",Cam bushes/crank nut ?
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A standard pump is fine on an unmodified engine but a sports engine with jets drilled out and a filter fitted an overbored pump is a good idea,vane pumps have a limited capacity due to only having one chamber and the more you increase the pressure the more load it puts on the pump. Rotary pumps have multiple chambers increasing the capacity and reducing the load on the pump, the vane pump can make high pressure but the load on the vanes would be more than the pump was designed for as I am sure you are aware of Dave. I know of engines using vane or double vane pumps but personally I would only use a rotary pump on a pressure fed engine. Terry.
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Charles ,
For interest , John Sutton did some tests on the standard A7 pump many years ago , mainly to confirm that it was not an inferior
piece of engineering unsuitable for anything other than a standard spit and hope engine.
Using SAE 40 oil, approx. 0.6 litres / 1000rpm / minute was delivered , approx. 3 litres at 5000rpm - John's figures.
I don't know what an oversized pump delivers , say 25% more , and with more than adequate pressure .
Good enough for my dashes up Harewood , Barbon , Prescott etc.,
Geoff
