With some time at home, I've pulled the engine out of the 997 Cooper.

The engine was rebuilt two years ago and I noticed the problem straight from the beginning, but haven't had time to pull her out till now.

The problem is that initially the oil pressure is fine, actually quite high (80PSI plus at idle) once the engine comes up to temp it then sits around 50 PSI at idle, but then take the car for a drive, and oil pressure drops at idle only to below 15 or 20PSI. That is only at idle however and not at any decent revs over 1500. I have heard that oil pressure of any sort is fine, but to expect 50 and get 15 is a little too much to leave alone.

I played with the relief spring and valve, I've played with oils and most other things I could while its together to try and work out what was going on.

I've got the engine apart now (now I've got my snazzy new engine crane) and I was hoping to find a set of buggered bearings, but as you can see in the images they're fine. No gouges, just a little polishing. Perfect in fact. So now I'm at an end. I've got an idea of (perhaps?) opening tolerances in the oil pump maybe? Could I be losing oil in the top end? Anyone got any ideas?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Check the shaft & rotor end float in the pump. It should only be a couple of thou, but recent pumps made in whereverland seem to have a fair bit.
Back in the day (`60s) we used to face the pump body a little if it needed it.
I think Clive Trickey suggested this, I've not read his books for 30 years so I'm not 100% sure it was him.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I've measured the endfloat on the oil pump after cleaning it out and drying it.
I get 40 thou (0.10 mm) endfloat.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

40thou is one mm,,, not .1 of a mm
big difference

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

It is 0.10 mm ( the dial gauge is metric) which still comes up as 0.03937 inches in my converter? Odd. I was using centimetres to inches...oops

But yes I see, 0.1/25.4 = 0.0039 which is 4 thou, thanks Matt

By the manual that seems fine. The workshop manual for the original 60s pumps mentions 4 thou being usual when measured with a straight edge and 6 thou requiring replacement.

Using the straight edge however, the outer rotor is 3 thou narrower than the inner, so the total gap for the outer rotor if there is 4 thou gap for the inner will be 4 plus 3 thou for a total of 7

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

The 2 rotors should be the same width, I'd be buying another pump... they are cheap as these days.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Will do, they are cheap as chips.

The oil gallery plugs are in place and look fine, the bearings also looks fine although I haven't pulled the camshaft.
I will do make sure my ducks are in a row before I put it back together, can you recommend anything else before I put it back together?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Those bearing shells don't look too hot now, I'd change all them too. Are cheap.
I like ACL Duraglide ones these days, made in Oz (tassie).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ok, will do.

In the flesh they are they are however very good. There's no scoring even if the photos don't show up well.

The problem with the Xmas period is that everything is shut!

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Karcraft said they open again on the 2nd, so that may help.

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I would have the crank journals measured.
My Cooper S had exactly the same symptoms as you describe and the crank was on the outer limit of the specifications. I have since had the crank ground and now I have around 50lb when hot @ 1500 rpm.
My crank looked OK with no scores or marks, just worn after over 100 thousand miles.

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Hi Michael

I made these measurements last night and got the following:

- Big ends come up as 1.595-1.596 at smallest measurement (30 thou under)

- Mains come up as 1.721 at smallest (again for 30 thou under)

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Ball bearing oil pressure relief valve fitted

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"Show me the Mini!"

Ha ha, I've played with that spring, valve and seat a lot.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Look at the oil you are using??? But first. I agree with the Doc, new shells

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"Show me the Mini!"