15 replies to this topic

[DeadSquare]

Does anyone know, or know where I can read up about, the pressure at which the average power steering operates ?

[Steve220]

On a classic mini?

[DeadSquare]

On a classic mini?

Not quite Classic Mini.

I have been toying with the idea for some years, that if the cast Iron block in the rear of my Unipower GT  was replacing with an aluminium one, it would improve the handling.

There is no where on the block that I have in mind to locate an oil pump. but in years gone bye, Lucas made a Dynamo with provision to bolt a power steering pump onto the commutator end.

[mpialan]

Why not use electric power steering?

[DeadSquare]

Why not use electric power steering?

 

I am not looking to ease my steering.  I want to know if a hydraulic power steering pump would provide enough pressure to lubricate the crankshaft etc: of a 5 bearing, 1200cc engine.

[Spider]

Some can make up to 1000 PSI, but only short term rated at that pressure and have a flow rate 10 - 15 gallons per minute, but that's with light grade oils, I think you could cut that down a fair way on an engine oil.

[DeadSquare]

Some can make up to 1000 PSI, but only short term rated at that pressure and have a flow rate 10 - 15 gallons per minute, but that's with light grade oils, I think you could cut that down a fair way on an engine oil.

WOW ! ........1,000 psi.   I don't think that the oil cooler would stand that, Lol.

I asked an old Mechanic, and he guessed about 50 psi.

 

It looks as though I'll have to machine a block to go on the end of the dynamo, incorporating a Mini pressure relief valve, and cut down an A Series oil pump, because it won't be rotating at 1/2 crankshaft RPM.

[Spider]

I did say 'some' ! But most do run higher pressures, that way, they only need very small piston areas in the racks and that gets the size of them down to something compact.

Gotya on a Dynamo mounted pump and the speed it'll be turning at. I'd suggest trialing that in a simple set up first as these being an the type of pump they are, they would have an upper 'speed' limit, eg, I do know off hand, gear pumps (also positive displacement like these) have an ideal speed range of 600 - 1000 rpm. They will work above that, but losses mount and then after certain speeds, they will cavitate.

[DeadSquare]

I have been trying to find a way of incorporating the engine's original gear pump, which runs at crankshaft rpm, but it is part of the block casting, and even if I could chop it off another block, when I turned it round to go on the back end of the dynamo, it would be rotating in reverse and the pressure relief valve wouldn't work if I swapped the inlet and outlet with each other.

 

A classic Mini oil pump probably runs at about 2,000 rpm, peaking at 3,000 when the valves bounce but touching 4,000 rpm in a race engine.

 

I used to weld a pressed steel crank pulley in place of the small dynamo pulley, when racing, but that would only get me to crank speed, which could peak at 10,000 rpm plus.

 

Reducing the diameter, and therefore belt contact area, of the crank pulley, would help, but that might not cope with the water pump and dynamo, without the extra load of the oil pump.

[Homersimpson]

The original MK2 Jag one (bolted to the back of a lucas Dynamo) ran about 850PSI I believe, the later XJ6 pump was around 1200PSI so way too high for what you are after I would suggest.

[Ethel]

Is there not a different oil pump you can adapt? O Series had one that bolted over the crank nose & my Pug diesel had one that was  virtually self contained, sucked straight from inside the sump with its own sprocket.

 

Oil won't be compressible, the pressure comes from stretching what's containing it, so if it flows through a restriction so it can flow away faster than it flows in the pressure will drop. It's the volume of flow you really need - pump displacement  x rpm.

[DeadSquare]

The original MK2 Jag one (bolted to the back of a lucas Dynamo) ran about 850PSI I believe, the later XJ6 pump was around 1200PSI so way too high for what you are after I would suggest.

 

Thank you.  That answers the question that I asked.  A power steering pump would have more (way more) than adequate pressure.

 

As someone who knows to what I am referring, do the power steering pumps have a pressure relief valve built into them ?.. If so, does the bleed feed back to the reservoir or just 'short circuit' to the inlet ?

[DeadSquare]

Is there not a different oil pump you can adapt? O Series had one that bolted over the crank nose & my Pug diesel had one that was  virtually self contained, sucked straight from inside the sump with its own sprocket.

 

Oil won't be compressible, the pressure comes from stretching what's containing it, so if it flows through a restriction so it can flow away faster than it flows in the pressure will drop. It's the volume of flow you really need - pump displacement  x rpm.

 

Thank you, my first thought was the O Series oil pump, but unfortunately it is too chunky  and doesn't leave enough room for the crankshaft cam pulley.

 

I have looked at various different oil pumps, the problem is driving them.  I have also considered an electric option, like a dry sump scavenge pump.

 

The problem is integrity, hence the change from 'pin drive' to 'star drive' between the A Series cam and pump.

 

If the engine can keep running without the oil pump working, it's not good, so oil pumps are engineered to keep working until something else stops the engine, such as a snapped timing chain.

 

Driving it from the cam belt involves several difficulties, and mounting from a cam cover wouldn't be very secure or convenient, in order to drive it through a cam pulley.

 

I know that in mounting the oil pump on the dynamo, I risk a fan-belt failure, but I would get an oil and ignition warning light.

 

It is beginning to look as though I will have to machine a bespoke body out of an aluminium billet.

[Ethel]

I'd think you could machine a fair bit off most pumps, they are made to fit where they can bolt on. A belt drive pump is going to have the oil seal you need, which is why I'd consider one, even if I wanted to spin it by a different method.

 

Engine oil pressure is much more a function of how quickly it leaks back to the sump. If you have an oil gauge plumbed on the end of the main gallery that'll be pretty much what the crank journals get. They create their own pressure, they just need the amount of oil going in to keep up with the oil going out.

[Homersimpson]

 

The original MK2 Jag one (bolted to the back of a lucas Dynamo) ran about 850PSI I believe, the later XJ6 pump was around 1200PSI so way too high for what you are after I would suggest.

 

Thank you.  That answers the question that I asked.  A power steering pump would have more (way more) than adequate pressure.

 

As someone who knows to what I am referring, do the power steering pumps have a pressure relief valve built into them ?.. If so, does the bleed feed back to the reservoir or just 'short circuit' to the inlet ?

 

The Jaguar MK2 power steering pumps have the relief valve built into them and I assume thats the standard arrangement for most (if not all) PAS pumps, the valve must just short circuit to the inlet as they only have two pipes, one from the reservoir and one to the steering box so no ability to return to reservoir.

 

Just to add that i've fitted a rack conversion to my latest MK2 that uses an electrically driven pump from a Vaxhuall Astra, this is a fairly simple pump but does I belive have a speed input that isn't used on the MK2.  If you could get this to work you might be able to turn the pump and hence the pressure down, not sure if I would trust this for engine lubrication though!

Edited by Homersimpson, 21 May 2023 - 11:21 AM.