27 replies to this topic

[Lenhamracer]

Dear Mini friends

 

there must be a problem with the oil pressure relief valve on my cooper S rally car. Suddenly oil pressure drops while idling and a while pressure is back. The engine has been completely refurbished with new pump and so on. Pressure is fine but as I said, it suddenly drops. But not regulary, sometimes it stays...

Might it be the relief valve? I have changed it as well as I had the same problem with this engine before the rebuild once. I don´t want to ruin the new engine...

Any ideas?

 

Thank you very much

 

Thomas

[GraemeC]

I don’t think the PRV would cause that issue - it would have to randomly open. I suppose if you have very good oil pressure it could open to regulate that and then stick occasionally, but I find that unlikely.
What’s your normal cold pressure at idle and at revs?
Is it the standard PRV shuttle, spring and cap?

[Lenhamracer]

cold and idle I would say 40 and at revs up to 75. It seems like a sticking PRV or not?

[Spider]

I can't see it being a sticking valve as you say there is Oil Pressure at Idle and then (sometimes), it will drop off and then after a spell come back. 

 

If it was sticking, it would drop off to zero right away. It could come back if the sticking valve is just sticking and not jammed, in that it might close slowly.

 

It is an odd one.

[carbon]

cold and idle I would say 40 and at revs up to 75. It seems like a sticking PRV or not?

I have the same question as GraemeC, Are you using the standard PRV shuttle, spring and cap?

 

In my experience the ball bearing conversion can be troublesome.

[Boycie]

Sounds like a faulty gauge to me!

[carbon]

If the oil pressure gauge is mechanical then I would trust it as a very reliable indicator.

 

I have never had one of the Smiths mechanical oil pressure gauges fail on me. The one I had fitted with the ball bearing pressure relief valve went up to over ~125psi (way past the 100psi marking, all round the gauge...) one cold morning and then the oil gallery plug popped. 

 

This Smiths oil pressure gauge still works perfectly, but I have never used a ball bearing for pressure relief since then.

[Spider]

,,, went up to over ~125psi (way past the 100psi marking, all round the gauge...) one cold morning and then the oil gallery plug popped.

 

Well,,, that one way of getting them out,,,,

[Retroman]

Might save some time and faffing drilling tapping and pulling the old solid brass plugs out...

 

Braze a 1/8npt to an air line fitting, wind the compressor regulator up and stand back !!

[carbon]

You might need a lot more than 125psi to shift the solid brass oil gallery plugs... the one I blew out was the pressed brass dome type

[Spider]

You might need a lot more than 125psi to shift the solid brass oil gallery plugs... the one I blew out was the pressed brass dome type

 

How about screwed plugs? 

[Retroman]

Gun powder ?

[Rorf]

Could even be a blocked oil intake pipe; engine has just been rebuilt so could be full of excess RTV sealant. OP still hasn't mentioned what type of PRV is in place.

 

Also common to dislodge the intake O ring when mating the engine and gearbox together.

[mini13]

I'm going to say a ball bearing prv could be the issue, as they can "bobble about" in the flow of oil and give variable readings. Avon bar used to sell a cup that sat between the ball and spring to keep it centralised.

Also much overlooked with the ball and spring is that the spring needs cutting down significantly to gat anything like a sensible pressure.

[gazza82]

Also much overlooked with the ball and spring is that the spring needs cutting down significantly to gat anything like a sensible pressure.

Or you buy the shorter spring that comes in the ball-type kit.