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Gear type pump pressure relief valve
#21
Just to put that figure in perspective it is 0.6cc of oil per revolution of the crankshaft.
Presumably that's the output of the pump, so ignores losses on the way to the bearings.

Is it known what temperature the oil was at? It would have a very significant influence on the result.
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#22
I've only ever had 'spit and hope' engines and pretty much all of them have had over-bored standard oil pumps. Mostly done for me by Dave Dye; I've lost count of how many he's done for me. When warm, pressure at idle is normally around 5 - 6 psi, running it varies with revs, obviously, but around 15 psi at 5000rpm. The only exception to this was the engine in my Trials Car when first built in 2012. The pressure gauge is one that goes up to 60 psi (because I happened to have it available) and that never read less than 30 psi when running and 40 psi when revved. Same set up as normal and all a bit of a mystery. I recall putting a post about it on the old Friends Forum. The engine was run in as normal and its first event was the 2012 Welsh Trial. We did the 100 miles with no problem and our first two hills were at Smatcher. Cleaned both using 'plenty' of revs but when we set off for our next hills, a rattling noise indicated a failed big end.

Investigation proved that the oil jets had been home made by a previous owner of the crankcase and instead of a straight drilling, had been made to a venturi profile, internally, effectively restricting the flow through them and increasing the gauge pressure. The conclusion was that the pressure through the jets was too high causing the oil to 'bounce' at high revs when it hit the crank troughs rather than go where it was needed. A re-metalled big end and a pair of new oil jets solved the problem, the pressure on the gauge went back to normal, and in the subsequent 7 years it's been fine despite being revved to death many, many, times.

My point in all this that pressure isn't everything in a 'spit and hope' engine and, in excess, can be detrimental.

Steve
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#23
I quite agree Steve, pressure is generated by resistance to flow and you only want as much as is needed to deliver the oil where it is required (but no less!)
In such a case where oil is forced to flow through a small orifice or venturi, the sudden acceleration of flow and subsequent pressure drop might well result in aeration of the oil, which is not a good thing at all.
In any engine, splash or pressure fed, a sudden unexpected high pressure reading is cause to stop the engine immediately and investigate (though in the case of your trials car I can easily understand that the cause was not spotted).
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#24
This was the traditional approach to more oil flow
The shaft isn't bent, the photo makes it look that way

   
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#25
Did the original pressure fed Austin sports engines use standard pumps?
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#26
Hi Chris,
Happy New Year.
The Nippy three bearing pressure fed engine used the standard oil pump.
The engine I had a play with was pretty original even down to the pistons and brass pin caps.
I did not compare the spring with a standard one but I suspect that the spring was either packed or a stronger one was fitted to give 30 PSI.

I too have a Paul Bonewell pump waiting to got into a pressure fed two bearing Nippy engine.
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#27
And a happy new year to you too!

That is interesting; of course the Nippy three bearing engine was fed from the centre main (like my Reliant crank engine, which also uses an - over-bored - Austin pump). My limited grasp of the science suggests that's a more favourable arrangement than feeding from the front end.
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#28
Hi Chris,
You still need the same amount of oil to flow in both systems given the same bearing clearances.
The two bearing pressure fed engine has further for the oil to travel to get to No 4 big end and if things are a bit worn then No 4 will be the first to suffer. (oil loss from the camshaft bearings has a huge effect on pressure and flow )
With modern cranks and shell bearings we are in a better place.
I would not use an original pressure fed crank with the way I drive the Type 65.
I run at 60 psi with my Allen Crank I only change gear when I run out of revs but have to use at least 2500 rpm as a minimum due to silly camshaft and can run up to 6500 rpm with a standard manual dizzy. ( at 30mph I have to be in third gear or it bogs )
I have changed the big end shells four times since 1995 with no regrinds.
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